MODIFICATION METHOD FOR THE HALLOYSITE MINERAL AND HALLOYSITE MODIFIED VIA MODIFICATION METHOD

Subject of the Invention

The invention relates to a modified halloysite modified and provided with functional properties without damaging the nanotube contents and a modification method for obtaining said modified halloysite.

State of the Art

Halloysite is a mineral belonging to the kaolin group and exists in the form of nanotube during its formation in the nature. In this mineral having a stratified structure as in the minerals of the clay group, the layers, unlike those of the other minerals, bend into a nanotube form due to their surface loads and stabilities. However, not every halloysite in the nature has the same shape; they have different properties because of their impurity contents, the presence of the wall rocks, the form of the developed tubes and the water content of the tubes.

According to the state of the art, halloysite has usage in the porcelain industry. As a result of the impurities it contains and its surface properties, it may not be used in the other fields, especially in the polymer structures, in the paint structures and as a catalyst where its nanotube contents could provide contribution.

The works involving halloysite and the products obtained following manufacture find the possibility of use commonly in the ceramic industry. Generally, it is used in the porcelain production for obtaining transparency owing the advantage provided by its nanotube structure. However, the porcelain manufacturers, after purchasing these products sold in raw state, use the same in their recipes after grinding and sieving. Because of the loss of the tubular structures following the sintering in the practices where the firing process at elevated temperatures is realized, an application such as the use of halloysite for the purpose of controlled release or as a nanocontainer is not possible either for the ceramic industry.

The use of powder minerals is common in the polymer, paint and coating industries; however, the works performed with halloysite in these fields are limited. The works aiming weight reduction or cost reduction are possible to be performed with the minerals used generally for the purposes of filling. Talc and calcite are the most commonly encountered products used in this scope. In the applications other than these, the use of clay derivative minerals is observed, though to a lesser extent. On the other hand, there is not available an adequate number of studies able to be performed on the use of halloysites in these fields, for the reasons that the halloysite reserves are limited in the world, that it is not possible to realize the purification and modification works simultaneously and also that the works are executed with halloysites of different characteristics.

When used in powder form, it is very difficult for the halloysite mineral in its current state to achieve the desired effect and homogeneous distribution in the material to which it is to be added, due to both its impurity contents and the incompatibility of its surface with the matrix material. Consequently, its use is not currently preferred in the above-mentioned fields. Even though its use may be possible as a fiber-like component only in cases where an increased strength is desirable, it is necessary to fill in the container structure, i.e. the tube, with an additive/agent that would confer the desired effect to the product in order for the use of halloysite to become possible for the purpose of obtaining different effects (UV barrier, antimicrobial, antibacterial, antiscale, anticorrosive, moss and algal growth prevention).

According to the state of the art, the additives conferring said properties are added directly to the textile product, paint and polymer formulations or a surface coating process is performed for these applications. Conferring said properties in such practices may generally be achieved by way of application of the additives/agents in liquid state on the surface. However, it is not possible to achieve controlled release and the effect of the agents used in liquid state is observed to decrease over time in such practices. Accordingly, the unavailability of materials, which are capable of performing controlled release and thus enabling a prolonged effect to be achieved, as well as the necessity to make it possible for these materials to be fed in powder form in cases where it is not preferred or possible to perform the same in liquid state represent a drawback encountered in the state of the art. On the other hand, it is not possible in the state of the art to apply said agents in powder form to the products, and further, the use of the halloysite mineral in powder form is not possible in the state of the art for the reasons mentioned above, representing a further problem of the state of the art that needs solution. Additionally, providing more than one property to a product at the same time is another problem aimed to be solved.

At this point, it was intended to modify the halloysite mineral for the solution of the problem that the halloysite mineral is not able to find the possibility of use in different fields. It was further intended to make it possible for different additives to be fed in powder form to thereby obtain a longer lasting effect as a result of the controlled release of the additives, owing to the use of modified (functional) halloysite, for the solution of the above-mentioned problems encountered in the state of the art.

With the invention, the modified halloysites having functionalized mineral surfaces are obtained by way of purifying halloysite, which has a nanotube content in its naturally obtained state but is unable to be used in any field other than ceramics, and doping, after the purification, the agents specified for the use of halloysite in different applications, such as polymer, paint and coating, in the nanotubes by preserving the tubular structure, and the method for obtaining said modified halloysites is described.

Object of the Invention

An object of the invention is to obtain a halloysite the impurities in the structure of which are removed without damaging the nanotubular structure.

Another object of the invention is to obtain a halloysite, which is purified without damaging its physical and morphological structure and which is made open to surface binding. Another object of the invention is to obtain a halloysite, which is purified without damaging its nanotubular structure and which is conferred functional properties by modifying the same with various agents.

Another object of the invention is to obtain a functional halloysite, which is modified via surface, via interlayer space or via tube interior.

Another object of the invention is to obtain a halloysite, the UV barrier, impact resistance, thermal properties, strength and/or antimicrobial properties of which are improved as a result of modification.

Description of the Figures

Figure 1: SEM images of the product purified with hydrocyclone

Figure 2: SEM image of halloysite after wet grinding

Figure 3: SEM image of halloysite after dry grinding

Figure 4: XRD pattern of halloysite, which has been ground in the mill, expanded in water and sieved and subjected to centrifugation

Figure 5: SEM image after the purification by centrifugation

Figure 6: Comparison of XRD patterns of the halloysite samples after hydrocyclone and centrifugation

Figure 7: SEM image of halloysite after the clay expansion in the mill and the sieving

Figure 8: SEM image of halloysite after the purification by centrifugation

Figure 9: A graph comparing the starting halloysite with halloysite treated with the acid at 40°C while the pH is 1,5

Figure 10: A graph comparing the dry/wet grinding with the starting halloysite while the pH is 1,5 (room temperature - purified halloysite/quaternary ammonium salt: 1/0,3)

Figure 11: A graph comparing the dry/wet grinding with the starting halloysite while the pH is 1,5 (room temperature - purified halloysite/quaternary ammonium salt: 1/0,5)

Figure 12: A display showing the variation in the interlayer space values with increasing quantity of quaternary ammonium salt Figure 13: A graph comparing the interlayer space values according to different pH and temperature values

Figure 14: A comparison graph for the pH values at room temperature

Figure 15: SEM image of halloysite after acid activation

Figure 16: A representation of XRD patterns after the modification with vinyl benzylaminoethylaminopropyltrimethoxy silane (Silane A)

Figure 17: A representation of XRD patterns after the modification with n-octyltrimethoxy silane (Silane B)

Figure 18: A representation of XRD patterns after the alcohol addition and modification with vinyl benzylaminoethylaminopropyltrimethoxy silane (Silane A)

Figure 19: A representation of XRD patterns after the alcohol addition and modification with n-octyltrimethoxy silane (Silane B)

Figure 20: A representation of XRD patterns after the sulfuric acid addition and modification with vinyl benzylaminoethylaminopropyltrimethoxy silane (Silane A)

Figure 21: A representation of XRD patterns after the sulfuric acid addition and modification with n-octyltrimethoxy silane (Silane B)

Figure 22: A representation of XRD patterns after the acetic acid addition and modification with vinyl benzylaminoethylaminopropyltrimethoxy silane (Silane A)

Figure 23: A representation of XRD patterns after the acetic acid addition and modification with n-octyltrimethoxy silane (Silane B)

Figure 24: Comparison of the trials performed with vinylbenzylaminoethylaminopropyltrimethoxy silane (Silane A) in different dispersing media

Figure 25: SEM image of the product with 1% silane content prepared with vinyl benzylaminoethylaminopropyltrimethoxy silane (Silane A) without using any dispersing medium

Figure 26: SEM image of the product with 1% silane content prepared with n- octyltrimethoxy silane (Silane B) without using any dispersing medium

Figure 27: Comparison of the trials performed with varying proportions of PEG 600

Figure 28: Comparison of the trials performed with varying proportions of PEG 1000

Figure 29: Comparison of the trials performed with varying proportions of eicosane

Figure 30: Comparison of the surface area values for all the thermal agents

Figure 31: Comparison of the trials performed with varying quantities of octadecane Figure 32: Morphological images (TEM) after the addition of the agent PEG 600 at 1%

Figure 33: Morphological images (TEM) after the addition of the agent PEG 1000 at 1%

Figure 34: Morphological images (TEM) after the addition of the agent eicosane at 1%

Figure 35: Morphological images (SEM) after the addition of the agent octadecane at 1%

Figure 36: Morphological images (SEM) after the addition of the agent octadecane at 10%

Figure 37: Morphological images (TEM) after the addition of the agent octadecane at 1%

Figure 38: Morphological images (TEM) after the addition of the agent octadecane at 10%

Description of the Tables

Table 1: Parameters in the process of purification with hydrocyclone (Study 1)

Table 2: Parameters in the process of purification with hydrocyclone (Study 2)

Table 3: Comparison table after the purification with hydrocyclone

Table 4: Comparison table for the post-purification surface area analyses

Table 5: Results of surface area analyses

Table 6: Conditions of the centrifugation study

Table 7: Grain size distributions after the purification studies

Table 8: Comparison table for the post-purification chemical analyses

Table 9: Comparison of the post-purification physical and mineralogical analyses

Table 10: Data of the modification trials performed with acid and quaternary ammonium salt

Table 11: Modification tests conducted without performing any preliminary process

Table 12: Modification tests conducted with alcohol addition

Table 13: Modification tests conducted with sulfuric acid activation

Table 14: Modification tests conducted with acetic acid activation

Table 15: Effect of dispersing medium, silane type and silane quantity difference on the surface area

Table 16: Filtration times

Table 17: Thermal agent testing set

Table 18: Effect of the quantity and type of thermal agent on the surface area and filtration time

Table 19: Effect of the quantity of octadecane on the surface area and filtration time Table 20: Comparison of the diameter and length values following the modification with the addition of the thermal agent at 1%, based on TEM results

Detailed Description of the Invention

The invention relates to a modified halloysite modified and provided with functional properties without damaging the nanotube contents and a modification method for obtaining said modified halloysite.

More particularly, the invention relates to a modified halloysite, which is purified and rendered open to surface binding and provided with functional properties by way of being modified with different agents in such a way that the nanotube content of the same is preserved and the physical and morphological structure of the same is not damaged, and to a method for the production of said halloysite.

Within the scope of the invention, the properties of the halloysite mineral were determined following the purification of the same via different methods and whether the tubular structure was deteriorated was examined, and the functional halloysites were obtained by conducting modification studies with agents chosen for different purposes.

During the first stage of the studies within the scope of the invention, the identification of the reserve characteristics and of the purification techniques for obtaining the halloysite mineral was carried out. Obtaining the functionalized mineral surfaces by way of purifying halloysite, which has a nanotube content in its naturally obtained state but is unable to be used in any field other than ceramics, and doping, after the purification, the agents specified for different purposes in the nanotubes by preserving the tubular structure and ensuring that the halloysite preserves its properties after the modification process are the main objects of the study.

The modified halloysite obtained within the scope of the invention is modified after the purification process. The product obtained as a result of each modification performed for different purposes is a functionalized powder halloysite product. While the obtained product may be used in the textiles for the thermal camouflage application, it is also possible for the same to become a powder antimicrobial mineral by the use of an antimicrobial additive. With the method developed within the scope of the invention, it is aimed to enable the use of the mineral for controlled release or as a nanocontainer.

In the methods developed within the scope of the invention, the trials were conducted with different agent contents to determine the point by which the mineral could be bound and the effects of binding.

Unlike the solution-based liquid structures according to the state of the art that are added to the finished product or applied on the product surface, it is aimed with the product developed within the scope of the invention to obtain a product, which does not only stay on the surface but is also released in an integrated manner as it is present in the main structure of the material. The material, which is doped in the halloysite mineral in the study conducted within the scope of the invention, is intended to be carried and adds functionality, will exhibit a longer lasting effect by way of being released as a result of friction, contact and/or heat in the course of time. With the halloysite mineral, which is rendered suitable for modification with different additives within the scope of the invention, it is intended to solve said problems of the state of the art by way of using said mineral as a nanocontainer and enabling said mineral to be bound by the surface to the interior of the materials desired to be carried in different applications.

Within the scope of the invention, in order to create the possibility of use in the other industries and different fields in addition to the use in the ceramic industry, the use of purified halloysite as well as the modification of the same with different agents/additives for various purposes were realized following the purification of the halloysite mineral. Within the scope of the invention, a halloysite mineral was obtained, which is provided with functional properties and which is suitable for use in powder form capable of being added to the matrix structures.

The method for the production of modified halloysites according to the invention basically comprises three steps. These steps are purification, modification, and drying and grinding. Purification

The primary goal of the purification process is to bring the mineral into a state that is open to surface binding. Avoiding damage to the physical and morphological structure of the mineral and preserving the nanotube content are among the critical features of the purification process.

The first step of the purification process is the dispersion of the clay in a mill. In this step, halloysite is enabled to disperse in water and the obtained sludge is sieved to remove the coarse-grained and/or hard minerals and the foreign matter like sand and quartz possible to be present within the mineral. Said sieves may be preferred to have a size of 63 microns and/or 125 microns.

Purification with a hydrocyclone:

In a preferred embodiment of the invention, the purification is accomplished by means of a hydrocyclone. It is desired that the nanotube structures have not been damaged and the coarse-grained and hard minerals have been removed from the material after the purification. The impurity value of the product after the purification process is determined by the properties of the starting material as well as the qualities and settings of the equipment used. The cyclone diameter, the cyclone top outlet (vertex) and the cyclone bottom outlet opening (apex) of the cyclone used in the process of purification with hydrocyclone affect the grain size distribution of the product to be obtained. It is necessary to determine the parameters appropriate for obtaining a product of desired quality. In a preferred embodiment of the invention, the cyclone diameter, the cyclone top outlet (vertex) and the cyclone bottom outlet opening (apex) are selected as 0,5"-l,5"; 5-7,5 cm and 1,5-4 cm, respectively.

Two different studies were conducted for the purification with hydrocyclone during the realization of the invention. In the first purification study with hydrocyclone, the input weight per liter was set to 1055 g/L, the cyclone top outlet (vertex) was set to 7,0 cm and the cyclone bottom outlet opening (apex) was set to 3,2 cm. In the third stage, the cyclone top outlet (vertex) was set to 5,5 cm and the cyclone bottom outlet opening (apex) was set to 3,2 cm. At the end of the second stage, 90% of the sample remained below 17,2 microns and 100% of the sample remained below 40 microns. At the end of the third stage, 90% of the sample remained below 13,13 microns and 100% of the sample remained below 45 microns, and the average grain size was found as 3,2 microns. In said study, the input halloysite values are 1055 g/L, dlO: 0,297, d50: 8,361 and d90: 42,606, and 100% of the material is below 75 microns. Said study is conducted under a pressure of 1,5-2, 5 bars, preferably 2 bars. The values for the respective study are shown below.

Table 1. Parameters in the process of purification with hydrocyclone (Study 1)

In the second hydrocyclone study, the purification was performed in 2 stages. The first stage weight per liter was determined as 1060 g/L, the cyclone top outlet (vertex) was set to 7,0 cm and the cyclone bottom outlet opening (apex) was set to 3,2 cm. The under cyclone weight per liter was found as 1160 g/L, while the above cyclone weight per liter was found as 1060 g/L. This shows that denser material passed to the bottom of the cyclone. The same sample was passed through the system one more time under the same conditions and finer material was enabled to be obtained. In this stage, the under cyclone weight per liter was found as 1154 g/L, while the above cyclone weight per liter was found as 1044 g/L. The average grain size of the sample at the top of the cyclone was found as 6 microns at the end of the first stage. After the second stage, this value dropped to 3,8 microns and 100% of the material was enabled to be under 40 microns. In said study, the input halloysite values are 1055 g/L, dlO: 0,297, d50: 8,361 and d90: 42,606, and 100% of the material is below 75 microns. Said studies are conducted under a pressure of 1,5-2, 5 bars, preferably 2 bars. The values for the respective study are provided below.

Table 2. Parameters in the process of purification with hydrocyclone (Study 2) The determination of solid concentration was performed by taking specimens from the samples passed through the hydrocyclone. Accordingly, the solid concentration following the hydrocyclone study was found as 9,8%. It was observed that 100% of the product was below 40 microns and the average grain size was about 4 microns.

Within the scope of the studies, analyses were performed for determining the properties of the halloysite purified with hydrocyclone and the chemical and mineralogical properties of the products are given in Table 3.

Table 3. Comparison table after the purification with hydrocyclone

Since the purification studies were performed by following the sieving and hydrocyclone stages, the analyses were performed by taking samples from each stage. According to the analysis results, it is considered that the coarse-grained quartz mineral was removed from the system after the sieving process. It can be seen in the results of XRF that the SiCh content increased in the sieve-top sample. It was determined as a result of the mineralogical analysis that the quartz quantity decreased when this process was followed by the hydrocyclone stage. Since the halloysite and metahalloysite phases were detected in the sample over 125 microns, the refeed was performed into the system to enable the expansion in water and the recovery of the sample. The sample separated as waste after the studies was also examined. According to the results of chemical analysis, the quantities of SiOz, NazO and K2O were observed to increase also in this sample. Hence, it was seen and confirmed by the results of mineralogical analysis that the coarse-grained quartz and feldspar minerals were possible to be removed from the system.

The surface areas of the specimens taken from these samples were also monitored. Since the surface area of the coarse-grained minerals will be small, it is considered that they will accordingly reduce the average surface area value. Therefore, the determination of surface area was performed before and after the purification to determine whether the surface area had a tendency to increase after purification, i.e. whether the fine material was obtained.

Table 4. Comparison table for the post-purification surface area analyses

According to the analysis performed, the waste and sieve-top samples gave similar surface area values. It is believed that the values higher as compared to the standard sample were obtained as there was still some amount of halloysite in these products. To the contrary, the surface area value increased in the purified sample. Accordingly, it could be seen that the samples with fine grains and wide surface area could be obtained in the purification process. The specific surface area was increased to above 100-135 m ² /g after the purification.

Whether the tubes were damaged during the mixing and purification was attempted to be determined by means of SEM images. According to the morphological analysis performed, no change occurred in the shapes of the tubes during and after the mixing. The tube diameters and lengths did not change significantly. The SEM images of the product purified with hydrocyclone are shown in Figure 1.

As a result of the examinations performed, it was determined that the nanotube structures were not damaged after the mixing and purification processes. It was observed that the coarse-grained hard minerals were removed from the material after the purification with hydrocyclone. It was possible to realize the purification process.

In a preferred embodiment of the invention, the grinding process is performed in order to reduce the physical size of the product before and/or after the purification process. Said grinding process may be wet or dry grinding.

Within the scope of the invention, the impact of the wet and dry grinding studies on the halloysite tubes was examined. The wet and dry grinding studies were conducted in a jet mill or a hammer mill or a vertical shaft grinder. The water was used for the grinding performed in wet medium. After the ground halloysite was passed through 63-micron sieve, it was characterized by means of SEM and BET devices.

The SEM image of halloysite after wet grinding is shown in Figure 2 and the SEM image of halloysite after dry grinding is shown in Figure 3.

Table 5. Results of surface area analysis

According to the results of the studies on morphology, it was observed that no significant change occurred in the nanotube structures after wet grinding and dry grinding and that the structures remained intact. Since halloysite has a structure like a paper winding, this study was conducted in order to assess the length/diameter ratios of the tubes during the grinding as well as examine whether the tubes were deteriorated against the possibility of unwinding during the process of dispersion in water. No marked difference was observed in the tubes after the wet grinding and dry grinding and it is possible to employ both grinding methods depending on preferences and needs.

The purified halloysite product prepared after the purification with hydrocyclone was not dried as it would be mixed in the wet medium. Purification by ce

In a preferred embodiment of the invention, the purification is achieved by way of centrifugation. It is desired that the nanotube structures are not damaged and the coarsegrained and hard minerals are removed from the material after the purification. In the process of purification by centrifugation, halloysite expanded in water that is first passed through preferably 63 or 125-micron sieves is fed to the centrifugation unit and sized under the influence of the centrifugal force.

It was detected that halloysite (10 A) and metahalloysite (7,40 A) forms were present inside the mineral sample used in the analysis studies, the tube lengths were in the range of 200- 2000 nm and the tube diameters were in the range 40-100 nm. The tubes are open-ended and hollow and have high cation exchange values. In the purification studies conducted with this product, it was determined that the coarse-grained impurities were possible to be removed and the nanotube structures were not damaged in the meantime.

In the analysis studies conducted within the scope of the invention, 250 kg of halloysite was passed through 63-micron sieves and fed to the centrifugation unit. It was aimed in this study to be able to obtain a high quantity of the material under 15 microns. The trials were performed using a 118-mm plate such that the drum speed was 4000 rpm and the valve opening was 25%. The studies for the centrifugation trial were started at an input weight per liter value of 1060 g/L. At the end of the trial, it was found in the sedigraphy device that the average grain size was 0,809 micron and all of the material remained under 25 microns. The presence of a high quantity of fine material was detected also in the section where the coarse material was separated.

In a preferred embodiment of the invention, the drum speed is in the range of 2500-4500 rpm, the differential speed is in the range of 6-8 rpm, the plate size is in the range of 90-130 mm and the valve opening is in the range of 15-35%. The details of the centrifugation study are given below.

Table 6. Conditions of the centrifugation study

Since the clay particles are below the level of approximately 10 microns, the determinations in this study were made taking into account the volumetric indicator of this value. In Trial 1, clogging occurred and it was not possible to obtain a sample. The second trial was performed after cleaning the system. In Trial 2, the drum speed was reduced and the plate was replaced. Even after these changes, the system clogged after about 5 minutes. The system was observed to become clogged as the proportion of the material passing into the coarse part increased. All the material possible to be obtained from the coarse part is below 255 microns. No material was obtained from the fine part. In the third trial, the drum speed was kept the same while reducing the plate size following the cleaning. In this stage too, the clogging was encountered and the system passed into a state of excessive vibration. As a result, the trial was stopped and the cleaning was performed again. However, it was determined that all the material in the coarse part dropped to 166 microns. In the fourth stage, the drum speed was increased and the plate size was increased. It was observed that it was possible to obtain product from this trial. All the material in the fine part was detected to be below 25 microns. The average particle size was determined to be 0,809 micron. The value of weight per liter was determined for this product and the solid concentration value was found as 9,3%. This product has the quality of input for the modification.

Considering the trials conducted with the hydrocyclone, a finer product was obtained as a result of the trial conducted by centrifugation. The comparative results from the two methods are provided in the following table.

Table 7. Grain size distributions after the purification studies

According to the results of analysis, it was observed that the quantity of SiCh decreased, i.e. the coarse-grained quartz mineral was removed from the system, following the sieving process. XRD results also support this conclusion. The quartz and clay phases present in the blend sample were detected to disappear following the purification studies. An evaluation of the results of surface area revealed that the surface area increased after the purification. However, the surface area values were determined to be greater in the post-hydrocyclone samples.

The chemical properties of the products obtained after the purification are presented in the table below.

Table 8. Comparison table for the post-purification chemical analyses

Table 9. Comparison of the post-purification physical and mineralogical analyses As can be seen from the details in the tables, it was determined that the minerals of impurity were removed when the raw sample was enriched via hydrocyclone as well as via centrifugation and that the surface area values and the cation exchange capacity increased as the impurities were removed. The undesired phases were removed during the purification process. Since the quantity of halloysite increased in the remaining structure, the surface area values increased due to the presence of the nanotubes of the clay particles in the matrix in a greater quantity as compared to the previous condition. As the nanotube structure became predominant in the system, the surface area increased and the exchangeable cation value also increased. Further, when the raw product was expanded in water and sieved, the minerals coarse relative to the starting material were observed to begin leaving the system. Whereas only the metahalloysite phase is present in the fine product, i.e. the purified product output from the centrifugation unit, the gibbsite, alunite and a greater proportion of quartz phase are present in the coarse part, i.e. the waste. The surface area values rose from 79 to 82 m ² /g upon the removal of the impurities, and the surface area values increased to the levels of 110-140 m ² /g upon the increase of the fine- grained product content in the main structure after the purification and upon the nanotubes becoming predominant.

The XRD pattern of halloysite ground in the mill, expanded in water, sieved and subjected to centrifugation is shown in Figure 4. The purified product output from the centrifugation unit is coded as fine.

Whether the tubes were damaged during the mixing and purification was attempted to be determined by means of SEM images. According to the morphological analysis performed, no change occurred in the shapes of the tubes during and after the mixing. The tube diameters and lengths did not change significantly. The SEM image of the product after the purification by centrifugation is shown in Figure 5.

In short, it is possible to obtain the clay particles with nanotube content in both methods of purification performed using hydrocyclone and centrifugation unit. Besides, the purity increases and the surface area and the exchangeable cation quantity also increase. The comparative graph for the XRD patterns of the halloysite samples after the hydrocyclone and centrifugation unit is shown in Figure 6.

The SEM study was conducted with a view to make sure that the tube structures were not damaged in the purification by centrifugation.

It was determined that the tubes were preserved and the tube lengths increased up to 1 micron after the process of dispersion in water in the mill. In other words, no significant change was observed relative to the starting mineral. The SEM image of halloysite after clay expansion in the mill and sieving is shown in Figure 7.

According to the evaluation, it was found that the tube structures remained intact but decreases occurred in the tube lengths following the centrifugation. Since the separation is performed at the speed of 4000 rpm in the centrifugation unit, the fractures may occur as a result of the samples colliding with the drum or with each other. The SEM image of halloysite after the purification in the centrifugation unit is shown in Figure 8. Modification

In the method for the production of modified halloysites according to the invention, the process performed subsequent to the purification is the process of modification of halloysite. The halloysite mineral represents a stratified clay wound in the form of a spiral. The groups Al ⁺ and OH- are present on the interior surface of halloysite and Si ⁺ ions are present on the exterior surface. Accordingly, it is possible to bind various chemical materials to the system via both surfaces.

The purified halloysite is referred to as clay in the following descriptions.

Modification with quaternary ammonium:

In a preferred embodiment of the invention, the halloysite mineral is modified with quaternary ammonium salts. Said quaternary ammonium salt may be dimethyl dihydrogenated alkyl ammonium salt. Modification of halloysite with a quaternary ammonium salt may be used for the purposes of increasing the halloysite thermal resistance and flame retardation.

Raw halloysite, which has a hydrophilic structure, is required to be brought into a form that is favored by the polymers, i.e. the organophilic form. For this purpose, raw halloysite is brought into the organophilic form by way of an ion exchange reaction with the cationic surfactants containing the quaternary alkylammonium cations.

In a preferred embodiment of the invention, the ratio of purified halloysite (clay)/quaternary ammonium salt is in the range of 1 over 0,2-0, 6 by weight, i.e. in the range of 1/(0, 2 to 0,6) by weight. In more detail, 0,2-0, 6 unit of quaternary ammonium salt is used for 1 unit of clay. In order to determine the optimum quantity of the quaternary ammonium salt, the studies were performed with a ratio of clay/quaternary ammonium salt of 1/0,3 and 1/0,5 by weight. In order to observe the effect of the acid activation in the study, the pH adjustment was made by the addition of sulfuric acid and then the product was mixed with the agent. The trials were generally started by adding 45 g halloysite to 450 mL purified water, stirring with a mixer for about 15-20 minutes, and thoroughly expanding and homogeneously dispersing the clay in water. After the clay was expanded, the pH adjustment was made by the addition of H2SO4 according to the desired pH value. The excess acid was removed by treating the same with NaOH until the pH value increased to 9. The specimens were modified for 1 hour in a mixer by mixing the same with a given proportion of quaternary ammonium salt at the prescribed temperature. In order to remove the excess of quaternary ammonium salt from the specimens of modified halloysite, the treatment was performed with methanol with a volume numerically equivalent to the mass of the quaternary ammonium salt. The specimens obtained following the methanol addition were pressed in a filter press, the times for draining off the water content was recorded, and the filtered specimens were examined by XRD after being dried in a drying oven. The BET studies were then performed for some selected specimens. The information about the trials is provided in the following table.

Table 10. Data of the modification trials performed with acid and quaternary ammonium salt

The modification studies were performed with acid activation and quaternary ammonium salt. The stirring was performed by way of mechanical mixing. The interlayer spaces of 9,9 A and 7,2 A present in the purified halloysite are the characteristic values for metahalloysite and halloysite. As a result of the studies, it was observed that of the layers with the space 9,9 A and 7,2 A present in halloysite, the interlayer space of 9,9 A disappeared due to the acid treatment. The results show no change regardless of the modification type, modification temperature and quaternary ammonium salt content. This indicates that the interlayer space that disappears depends only on the presence of acid. Further varying the pH value did not change the result. In all the studies, the interlayer space of 9,9 A disappeared as a result of acid activation, but the 7,2 A interlayer space did not experience damage at all.

A comparison of starting halloysite and halloysite treated with the acid at 40°C while the pH is 1,5 is shown in Figure 9 and a comparison of the dry/wet grinding with the starting halloysite while the pH is 1,5 (room temperature - clay/quaternary ammonium salt: 1/0,3) is shown in Figure 10.

It is possible that halloysite may differ in the tube structures or in the modification processes as a result of being subjected to dry or wet grinding. This differentiation was examined in the presence of the agents. In order to examine said difference, a set was wet- and dry-ground and subsequently modified with different proportions of quaternary ammonium salt. As a result of XRD, no differentiation was observed in the surface modification studies performed following the wet and dry grinding. A comparison of the dry/wet grinding with the starting halloysite while the pH is 1,5 (room temperature - clay/quaternary ammonium salt: 1/0,5) is shown in Figure 11.

It was observed that the intensities of peak giving an interlayer space of 4.64 A generally increased with increasing quaternary ammonium salt (quat) quantity. It was interpreted that this peak was formed by the quaternary ammonium salt. The variation in the interlayer space values with increasing quantity of quaternary ammonium salt is shown in Figure 12.

Performing the modification of halloysite at different temperatures did not create a difference according to XRD results. Further, variation of the selected pH values generally does not exhibit a significant effect after the clay layers are spaced. For instance, it was found that no significant difference was present between the pH values of 1,5 and 2,5. A comparison of the interlayer space values according to different pH and temperature values is shown in Figure 13 and a comparison for the pH values at room temperature is shown in Figure 14.

In the surface modification process, which aims to form a hydrophobic surface, an analysis involving the determination of filtration time required for removing the water content present in the structure is performed. When the proportions of the quaternary ammonium salt were evaluated, the filtration times were observed to increase with increasing quaternary ammonium salt quantity. Since the interlayer space value of halloysite is lower than that of the clays with smectite structure, the system is locked and entirely surrounds halloysite when the quaternary ammonium salt in excess of certain proportions is charged. It is considered that the agent completely fills the tubes and has even a more than necessary quantity in such a case. A BET study was performed to verify the same. According to the study results, halloysite having a surface area of 79,70 m ² /g prior to acid activation had a surface area value of 0,32 m ² /g after acid activation (pH: 1,5). When this product was treated with quaternary ammonium salt (wet grinding - pH: 1,5 - 25°C), the surface area value rose to 1,02 m ² /g. Based on these results obtained, it is considered that the surface is damaged or the surface is entirely covered due to acid activation. A SEM image of halloysite following the acid activation is provided in Figure 15.

Therefore, in a preferred embodiment of the invention, the acid activation is not carried out. Based on the results, it was considered that the quantity of acid used was too much for activation. The crystal structure was impaired due to the acid used. It was found that the activation should be performed with a very small quantity of acid in case of performing acid activation for the modification process.

The method employed for the production of halloysite modified with quaternary ammonium salts is as follows:

• feeding, in wet or dry state, halloysite with a solid concentration of preferably 5-15%,

• mixing halloysite and 1-15% by weight quaternary ammonium salt for 45-95 minutes at a temperature of 50-80°C,

• cooling the mixture at room temperature, adding methanol to the mixture and stirring for 5-15 minutes, filtering the mixture, and drying at a temperature of 50-75°C.

While the modification process with the quaternary ammonium salt may be performed under a pressure of 1,5-2, 5 bars, it is also possible to realize the process without applying extra pressure. The filtration process is performed preferably in a filter press or by way of holding and draining.

The drying process is performed preferably in a fan drying oven or a vacuum drying oven or using microwave. The drying in a fan drying oven and in a vacuum drying oven is realized for 12-24 hours at a maximum temperature of 60-70°C, while the drying by the use of microwave is performed for 5-70 minutes.

For the microwave drying process in the method of modification with quaternary ammonium salt, silanes and agents, the trials were conducted at three feed and conveyor speeds, namely 10 - 20 - 30 kg/h, with a magnetic field level in the range of 20-80. The trials were conducted using the air cooling and water cooling types such that the magnetron power was 0,75-1,2 kW and the total installed power was 16-45 kW. The microwave frequency was set to 2450 MHz. No problem was detected in the layers and tube cavities of the finished product. In these studies, the overall duration was about 30 minutes at the lowest conveyor belt speed. The optimum drying time was observed to be 7-10 minutes. The output moisture ratio could be reduced down to 0,2%.

Modification with silanes:

In a preferred embodiment of the invention, halloysites are modified with different silanes. Owing to the modification of halloysites with silanes, improvement in the thermal properties, compatibility for the strength increase, increase in the scratch resistance and compatibility for the paint applications may be achieved. The silanes indicated below were preferably employed within the scope of the invention and it is also possible to perform the modification process by working with any silane with vinyl terminal group, amine terminal group or methoxy terminal group.

Said silanes with which halloysite was modified are listed below:

• Vinylbenzylaminoethylaminopropyltrimethoxy silane

• n-octyltrimethoxy silane

• aminoethylaminopropyltrimethoxysilane

While it is possible to modify halloysites with said silanes without any preliminary process, the modification may also be performed by way of dispersion in an alcohol, after sulfuric acid activation or after acetic acid activation.

Modification without using dispersing medium:

In a preferred embodiment of the invention, halloysites are enabled to be modified with silanes without using any preliminary process. The studies were conducted within the scope of the invention regarding the modification of halloysites with silanes in the absence of a preliminary process. The modification process was performed by taking 200 ml from the 10% halloysite sample, which was purified with a hydrocyclone and then expanded with water, and by adding silane in 4 different quantities, i.e. 10%, 5%, 2,5% and 1% by weight, respectively. These quantities were determined taking the active silane content also into account. The sludge, which was stirred for about 1 hour at 60-70°C after the addition of silane, was allowed to cool down to room temperature and was then washed with methanol in order to remove the silane molecules not adhered to the surface. The washed sample was filtered in a filter press and the filtration times were noted as they could be an indicator of the success of the modification process. The filtered samples were dried in a vacuum drying oven for 1 night at maximum 65°C and were brought into a state suitable for surface characterization by means of sample preparation processes. pThe samples subjected to modification are given in the following table.

Table 11. Modification tests conducted without performing any preliminary process

The method employed for the production of halloysite modified with silanes without performing any preliminary process is as follows:

• feeding, in wet or dry state, halloysite with a solid concentration of preferably 5-15%,

• mixing halloysite and 1-15% by weight silane for 45-95 minutes at a temperature of 50- 80°C,

• cooling the mixture at room temperature,

• adding methanol to the mixture and stirring preferably for 5-15 minutes,

• filtering the mixture, and

• drying at a temperature of 50-75°C.

The drying process is performed preferably in a fan drying oven or a vacuum drying oven or using microwave. The drying in a fan drying oven and in a vacuum drying oven is realized for 12-24 hours at a maximum temperature of 60-70°C, while the drying by the use of microwave is performed for 5-70 minutes.

While the modification process with silanes in the absence of a preliminary process may be performed under a pressure of 1,5-2, 5 bars, it is also possible to realize the process without applying extra pressure.

The filtration process is performed preferably in a filter press or by way of holding and draining. Modification with alcohol addition:

In a preferred embodiment of the invention, halloysites are enabled to be modified with silanes after dispersing a silane in an alcohol.

The studies were performed within the scope of the invention regarding the modification of halloysites with silanes following the dispersion of silane in alcohol. Silanes undergo hydrolysis to form silanols before binding to the substrate. If the quantity of silane added to the system increases, this could increase the quantity of alcohol forming as a result of hydrolysis and alter the behavior of silane. In order to observe the effect of the alcohol ratio in the medium on the behavior of silane, the reaction was carried out in an alcoholic medium. In this context, the effect of alcohol addition on the surface modification was examined. 100 ml of a 95% ethanol solution was used as the alcohol. After the alcohol-silane mixture was stirred for 15 minutes at 60-70°C, 200 ml 10% halloysite was added and the mixture was stirred for 1 hour at 60-70°C. After cooling down, the mixtures were washed with methanol again. The samples subjected to modification are given in the table below.

Table 12. Modification tests conducted with alcohol addition

The method employed for the production of halloysite modified with silanes dispersed in alcohol is as follows:

• dispersing silane in an alcohol, preferably in a 90-99% ethanol solution, by way of stirring preferably at a temperature of 60-80°C preferably for 5-25 minutes,

• feeding, in wet or dry state, halloysite with a solid concentration of preferably 5-15%,

T1 • mixing halloysite and 1-15% by weight silane for 45-95 minutes at a temperature of 50- 80°C,

• cooling the mixture at room temperature,

• adding methanol to the mixture and stirring preferably for 5-15 minutes,

• filtering the mixture, and

• drying at a temperature of 50-75°C.

While the modification process with silane dispersed in alcohol may be performed under a pressure of 1,5-2, 5 bars, it is also possible to realize the process without applying extra pressure. The filtration process is performed preferably in a filter press or by way of holding and draining.

The drying process is performed preferably in a fan drying oven or a vacuum drying oven or using microwave. The drying in a fan drying oven and in a vacuum drying oven is realized for 12-24 hours at a maximum temperature of 60-70°C, while the drying by the use of microwave is performed for 5-70 minutes.

Modification after sulfuric acid activation:

In a preferred embodiment of the invention, halloysite is enabled to be modified with silane after activation with sulfuric acid. The studies were performed within the scope of the invention about modifying halloysites with silanes after the activation of halloysite with sulfuric acid and thus being able to increase the surface area of halloysite and enabling halloysite to be bound by more agent. The acid used in the activation process reacts with the iron in the structure of halloysite to enable the same to be removed from the structure, which in turn increases the surface area of halloysite and provides the possibility for the binding of more agent to the surface.

The effects of acid activation were examined by adding acid to 200 ml of 10% halloysite. The addition of sulfuric acid was performed until the pH value became 10%, 5%, 2,5% or 1% by weight silane was added on the activated halloysite. Only for the trials using 10% silane in this test set, the pH was adjusted to 10 by sodium hydroxide (NaOH) following the step of addition of silane and it was thus aimed to remove the excess acid remaining in the medium. The test set information about the samples subjected to sulfuric acid activation is given in the following table.

Table 13. Modification tests conducted with sulfuric acid activation

The steps of the method for modifying halloysites with silanes following the activation of halloysite with sulfuric acid are as follows:

• feeding, in wet or dry state, halloysite with a solid concentration of preferably 5-15%,

• adding sulfuric acid until reaching the pH value of 1,5-2, 5,

• stirring at a temperature of 30-50°C to enable activation of halloysite in sulfuric acid,

• adding silane to the mixture,

• mixing halloysite and 1-15% by weight silane for 45-95 minutes at a temperature of 50- 80°C,

• cooling the mixture at room temperature,

• adding methanol to the mixture and stirring preferably for 5-15 minutes,

• filtering the mixture, and

• drying at a temperature of 50-75°C.

While the process of modifying with silane the halloysite that is activated with sulfuric acid may be performed under a pressure of 1,5-2, 5 bars, it is also possible to realize the process without applying extra pressure. The filtration process is performed preferably in a filter press or by way of holding and draining. The drying process is performed preferably in a fan drying oven or a vacuum drying oven or using microwave. The drying in a fan drying oven and in a vacuum drying oven is realized for 12-24 hours at a maximum temperature of 60-70°C, while the drying by the use of microwave is performed for 5-70 minutes.

Modification after acetic acid activation:

In a preferred embodiment of the invention, halloysite is enabled to be modified with silane after activation with acetic acid. The studies were performed within the scope of the invention regarding the modification of halloysite with silane after the activation of halloysite with acetic acid. Silane is not able to become immediately integrated in the system when it is added to the medium, which in turn may impair homogeneity by causing partial gelation. In order to overcome this condition, it is aimed to reduce the pH of the solution to 3, 0-4, 5 by the use of an organic acid such as acetic acid to thereby enable the reinforced material to reach the optimum performance. In addition, the acidic medium assists with the stability of silane and enables silane to be more stable and more easily oriented on the surfaces where it is bound. Further, it serves the function of a catalyst in the hydrolysis of silane, the first step required for the formation of the silane-halloysite complex. Consequently, the balancing of pH was performed with acetic acid within the scope of the study in order to enable silane to homogeneously bind.

After studying the effect of acid activation on the surface modification, acetic acid (CH3COOH) was used to examine the effect of the acid used and the pH of the medium. This process was performed by bringing 200 ml halloysite to 25°C and adding the acid until the pH value became 3-4,5. Following the acid addition, the steps of adding silane, stirring for 1 hour at 60-70°C, washing with methanol, filtering and drying were carried out and the samples were prepared for surface characterization.

Table 14. Modification tests conducted with acetic acid activation

The steps of the method for modifying halloysites with silanes following the activation of halloysite with acetic acid are as follows:

• feeding, in wet or dry state, halloysite with a solid concentration of preferably 5-15%,

• heating halloysite up to the temperature of 15-35°C,

• adding acetic acid until reaching the pH value of 3-4,5,

• adding silane to the mixture,

• mixing halloysite and 1-15% by weight silane for 45-95 minutes at a temperature of 50- 80°C,

• cooling the mixture at room temperature,

• adding methanol to the mixture and stirring preferably for 5-15 minutes,

• filtering the mixture, and

• drying at a temperature of 50-75°C.

While the process of modifying with silane the halloysite that is activated with acetic acid may be performed under a pressure of 1,5-2, 5 bars, it is also possible to realize the process without applying extra pressure. The filtration process is performed preferably in a filter press or by way of holding and draining. The drying process is performed preferably in a fan drying oven or a vacuum drying oven or using microwave. The drying in a fan drying oven and in a vacuum drying oven is realized for 12-24 hours at a maximum temperature of 60-70°C, while the drying by the use of microwave is performed for 5-70 minutes.

Results of the studies of modification with silane:

The halloysite nanotubes are the minerals containing voids 30-40 nm in diameter. The trials were performed within the scope of the study to fill in these voids or modify the surfaces with various agents. Following the method studies performed for the surface area measurements, the appropriate dimensions for halloysite were determined. While the surface area of the halloysite blend product was found as 79 m ² /g, this value rose to 130 m ² /g after the purification studies with hydrocyclone and to 116 m ² /g after the purification studies by centrifugation. The surface area values are expected to decrease in case the tube interiors are filled as a result of modifications performed with silane. Table 15 shows the variations in the surface area of halloysite modified by four different methods, according to the quantity of silane. Accordingly, the different surface area values are obtained due to the difference in the chain lengths. While greater surface area values are obtained with silane having vinyl benzyl amino group, smaller surface area values are found with octyltrimethoxy silane. According to the chemical contents, it is considered that the second silane type penetrates the system to a greater extent.

Lower surface area values are found when no dispersing medium is used. On the other hand, lower values than the surface area of the purified product are obtained in any way (surface area of the purified halloysite is 110-130 m ² /g). When the preliminary process is performed with alcohol, the surface area values show the tendency to increase relative to the samples without dispersing medium.

When halloysite was activated with various acids and silane was added subsequently, the surface area values showed the tendency to increase. In the study of activation with sulfuric acid, certain quantities of acid were introduced and the properties were examined. It was determined that the tube structures deteriorated when the acid quantity was excessive. The trial was performed by reducing the acid quantities based on a determined pH value. The surface area values increased after the acid activation and silane modification of halloysite.

When a comparison was made based on the silane quantities, it was found that the lowest surface area values were obtained in the cases where halloysite was added directly, i.e. in cases where there was no dispersing medium. The surface area values show the tendency to increase after the alcohol and silane are mixed. The surface area showed an upward trend following the activation performed with sulfuric acid. In the test set where it was aimed to effectively disperse acetic acid and silane, the surface area values had the tendency to increase relative to the trials performed without using any dispersing medium.

Table 15. Effect of dispersing medium, silane type and silane quantity difference on the surface area

The selected silanes tend to render the material on which they are coated hydrophobic. For this reason, the samples present in aqueous mixtures are filtered through the baroid filters prior to drying. The pressure is kept constant during this filtration. Starting from this, the mixtures obtained as a result of the trials were filtered and the filtration times were noted. These results enable an approximation about hydrophobicity to be made. The obtained results are shown in the following table.

Table 16. Filtration times

As a result of the studies performed, a relationship was determined between the silane quantity and the filtration time. According to this, the filtration times shorten, i.e. the hydrophobicity increases, with increasing silane quantity. A similar result was obtained for each dispersing medium and silane.

The variation in the interlayer space value in the obtained products was also examined by means of a X-ray diffractometer. The comparative results for the halloysite samples prepared without using any dispersing medium are shown in Figure 16 and Figure 17.

According to the XRD study performed, changes were observed, irrespective of the type of silane, in the peak interlayer space values (d) for halloysite and metahalloysite, which were initially 7,40 A and 10 A, when no dispersing medium was used for silane. According to the results, it was determined that the peak of 7,40 A remained the same, whereas the peak of 10 A shifted to 15 A upon an increase in the silane quantity. It is remarkable that the 10 A layer did not fully expand and did not fully shift to 15 A when the silane content was 1%. Above the silane content of 2,5%, the 10 A peak entirely disappears and converts into 15 A. Accordingly, it is considered that silanes entered the halloysite nanotubes and increased the tube diameter and interlayer space value. This increase in the diameter or the interlayer space value in turn increased the surface area values. XRD patterns following the addition of vinylbenzylaminoethylaminopropyltrimethoxy silane (Silane A) and alcohol and modification are shown in Figure 18, and XRD patterns following the addition of n-octyltrimethoxy silane (Silane B) and alcohol and modification are shown in Figure 19.

The variation in the peaks was examined after the alcohol addition performed in order to enable more effective dispersion of silane. These data give patterns similar to those of the systems without alcohol addition (without dispersing medium addition). As the addition of silane is performed, the 10 A peak of halloysite increases to 15 A. However, the 15 A peak is observed to be sharper when the alcohol addition is made. As the silane quantity increases, the intensity of the peaks increases.

XRD patterns following the addition of vinylbenzylaminoethylaminopropyltrimethoxy silane (Silane A) and sulfuric acid and modification are shown in Figure 20, and XRD patterns following the addition of n-octyltrimethoxy silane (Silane B) and sulfuric acid and modification are shown in Figure 21.

After the sulfuric acid addition and modification performed to increase the surface area of halloysite, the 10 A peaks were observed to completely shift to 15 A. No change was observed in the peak intensities and positions upon the increase in the silane quantity. Only for the trials where 10% silane was used in this test set, the pH was adjusted to 10 by sodium hydroxide (NaOH) following silane addition step and it was thus intended to remove the excess acid remaining in the medium. While no change occurred in the surface areas after this study, the filtration times increased. However, no change was observed in the XRD patterns.

XRD patterns following the addition of vinylbenzylaminoethylaminopropyltrimethoxy silane (Silane A) and acetic acid and modification are shown in Figure 22, and XRD patterns following the addition of n-octyltrimethoxy silane (Silane B) and acetic acid and modification are shown in Figure 23. The presence of the peaks 15 A and 7,40 A was also detected as a result of the studies performed with acetic acid. The 10 A peaks were not observed either in these results similar to the trials performed with sulfuric acid.

A comparison of the trials performed with n-octyltrimethoxy silane (Silane B) in different dispersing media is shown in Figure 24.

As a result of the characterization studies performed, a decrease was observed in the filtration times with increasing silane quantity. On the other hand, the upward and downward trends were observed in the surface areas according to each silane and medium. After the activation study performed with sulfuric acid, the surface area values increased as compared to the other studies. There is also difference in the surface area values in the study performed using two different silanes. The reason for this could be explained by the fact that silanes have different chain structures and behave differently when subjected to various preliminary processes (dispersing medium, temperature, etc.).

According to the comparison made between the XRD results, the interlayer space values (d) of 10 A and 7,40 A of halloysite show the shifting tendency after the processes. The halloysite peaks of 10 A increase to the level of 15 A, while the 7,40 A peaks are preserved. The intensity of the 15 A peak increases with increasing silane quantity. For the additions of 1% by weight where the silane quantity is the lowest, all of the interlayer space values of 15 A, 10 A and 7,40 A are observed.

When the modification with silane is performed, silane increases the interlayer space values of the halloysite nanotubes and expands the spaces. When a preliminary process is performed, i.e. when various chemicals like alcohol and acid are added, the surface area increases and the peaks remain the same. It was considered that this could result from the damage the dispersing medium causes in silane as well as the expansion of the tubular structure and the increase of the surface area due to the increase in the interlayer space value. Accordingly, it is thought that the surface area values and the filtration times could likewise increase. A SEM study was conducted in order to clarify this. The images of the morphological analysis performed with the products with 1% agent addition are shown in Figures 25 and 26. Based on the morphological analysis performed, no considerable difference was observed in the tubular structures. Occasional length reductions are observed due to the stirring processes being performed in a mechanical mixer and due to the grinding process being performed subsequently. However, the diameter increases are believed to occur. According to the evaluation made, the diametric widths generally in the range of 60-100 nm were measured, which is in parallel with the starting halloysites.

No difference in morphology was observed when a comparison was made for two different silanes. More clear tube structures were noted in the studies performed with Silane A. The images of the product with 1% silane content prepared with vinylbenzylaminoethylaminopropyltrimethoxy silane (Silane A) without using dispersing medium are shown in Figure 25, and the images of the product with 1% silane content prepared with n-octyltrimethoxy silane (Silane B) without using dispersing medium are shown in Figure 26.

As a result of the analyses, it was observed that the surface area values were within the most favorable range, i.e. the surface area values decreased as a result of the tube volumes being filled by the agents after the purification, and the filtration times were the smallest. The XRD comparison made reveals no difference among the four methods in terms of peak positions. Consequently, it was decided not to use a separate dispersing medium for halloysite or agents in the trials to be conducted with the thermal agents. Accordingly, it was decided to perform the addition of the agent after dispersing halloysite in water without using a dispersing medium and after heating the dispersion to 60-70°C.

Modification with thermal agents:

In a preferred embodiment of the invention, halloysites are enabled to be modified with thermal agents. Said thermal agents are polyethylene glycol (PEG) 600, polyethylene glycol (PEG) 1000, eicosane (C20H42) or octadecane (CisHss). Thermal camouflage may be achieved by the use of these agents. The studies were performed within the scope of the invention regarding the modification of halloysites with thermal agents in the absence of a preliminary process. Table 17. Thermal agent testing set

The modification process was performed with a phase shifter material. Eicosane and PEG 1000 are in solid form, while PEG 600 and octadecane are in liquid form. The solid agents with melting point above the room temperature were first brought into the liquid state by way of dissolving the same in a water bath and were added to the process at the ratios of 10%, 5%, 2,5% and 1% by weight. For eicosane, further trials were conducted with a ratio of 0,5% by weight at 60-70°C.

200 ml was taken from 10% halloysite purified and expanded with water without performing any activation process and different quantities of the thermal agent were added. Then, the mixture was brought to 60-70°C, stirred for 1 hour, and was allowed to cool down to room temperature at the end of the 1 hour period. After achieving the required cooling, the washing process was performed in order to remove the thermal agents not adhered to the surface. While methanol was used for washing the samples involving the use of PEG 600, PEG 1000 and octadecane, ether was used for the samples involving the use of eicosane that was determined to be insoluble in methanol. The washed samples were filtered in the filter press and the filtration times were noted as these could be an indicator for the success of the modification process. The filtered samples were dried for 1 night in a vacuum drying oven at 65°C and were rendered suitable for the surface characterization by way of sample preparation processes.

The method employed for the production of halloysite modified with thermal agents is as follows:

• first dissolving the thermal agent in a water bath in case said agent is solid,

• feeding, in wet or dry state, halloysite with a solid concentration of preferably 5-15%,

• mixing halloysite and 0,5-15% by weight thermal agent for 45-95 minutes at a temperature of 50-80°C,

• cooling the mixture at room temperature,

• adding methanol to the mixture for the embodiment using PEG 600 or PEG 1000 and adding ether to the mixture for the embodiment using eicosane and stirring for 5-15 minutes,

• filtering the mixture, and

• drying at a temperature of 50-75°C.

While the process of modifying halloysite with a thermal agent may be performed under a pressure of 1,5-2, 5 bars, it is also possible to realize the process without applying extra pressure. The filtration process is performed preferably in a filter press or by way of holding and draining.

The drying process is performed preferably in a fan drying oven or a vacuum drying oven or using microwave. The drying in a fan drying oven and in a vacuum drying oven is realized for 12-24 hours at a maximum temperature of 60-70°C, while the drying by the use of microwave is performed for 5-70 minutes. The surface area, filtration times and interlayer space values were observed with a comparative approach. Table 18. Effect of the quantity and type of thermal agent on the surface area and filtration time

The surface area tends to decrease with increasing silane quantity. However, no significant difference was observed in the surface area values when the agents PEG 600 and PEG 1000 were used. On the other hand, based on the filtration time values, the products with PEG 1000 content were determined to be filtered in shorter time. The surface area values turned out quite low as a result of the studies performed with the agent eicosane. The surface area value, which was 130 m ² /g after the purification, dropped to the levels of 40-75 m ² /g when modified with this product. It is considered that it is easier for this product to penetrate the halloysite nanotubes.

According to the XRD study performed with PEG products, the peak interlayer space of 10 A increased to the interlayer space value of 15 A, as was the case with silanes. Same interlayer space value (d) was obtained in both the PEG 600 and PEG 1000 samples and said value did not change despite the increase in the quantity. The comparison of the trials performed with different proportions of PEG 600 is shown in Figure 27 and the comparison of the trials performed with different proportions of PEG 1000 is shown in Figure 28.

The patterns belonging to the trials conducted with eicosane are shown in Figure 29. With this product too, the interlayer space values (d) parallel to those obtained with PEG 600 and PEG 1000 were obtained and were independent of the agent quantity.

The morphological study was performed for the samples with 1% thermal agent content. As can be seen from the SEM images, the tube structures were not impaired, but their lengths decreased. The tube lengths are generally 200-400 nm. It is considered that the diametric widths also changed. It was found that the diameter increases occurred and the dimensions were in the range of about 90-100 nm. The width increases are remarkable especially in the PEG 1000 sample. This provides an information parallel to the XRD results. The increases were also detected in the tube diameters, upon the interlayer space values (d) of normally 10 A shifting to the value of 15 A when the agent was started to be filled in the tubes. This explains the changes in the surface area values.

Similar width-length ratios were observed also in the halloysite products containing 1% eicosane. Diameter increases are noted in this trial also. Accordingly, the results found by XRD were in parallel with the SEM images.

Whereas changes may occur in the peak intensities upon an increase in the silane quantity, no quantity-associated pattern change was observed with the thermal agents. However, changes may occur in the surface area with increasing agent quantity. The only difference between the products PEG 600 and PEG 1000 is in the filtration times. The products containing PEG 1000 were determined to filter in a shorter time. When the trials performed with the agent eicosane were compared to the PEG analyses, it was found that the surface areas were small in the trials performed with eicosane, but there was no change in the XRD patterns.

Within the scope of the invention, the trial with the agent octadecane was also performed in addition to the above-mentioned trials with PEG 600, PEG 1000 and eicosane.

Table 19. Effect of the quantity of octadecane on the surface area and filtration time

As a result of the analyses, the surface area values decreased as compared to the surface area of the starting halloysite mineral, as expected. It was thought that the reason for this was the adherence of the surface modification agent to the active surfaces of halloysite, as was the case with the trials with silane, and this was considered as a favorable result. The surface area tends to decrease with increasing octadecane quantity. While the surface area of the starting mineral (purified halloysite) was 130 m ² /g, the surface area was observed to drop down to as low as 24,68 m ² /g following the surface modification. According to these results, it was determined that the surface of the starting mineral, i.e. the purified halloysite, could be coated by an extent in the range of 44-82%. The results are shown in Figure 30 for comparing the changes in the surface area with those resulting from the trials performed with the other thermal agents. An evaluation of the graph revels that the greatest surface area was reached by the addition of 1% PEG 600, whereas the smallest surface area was reached when 10% octadecane was added. It was considered according to the BET results that octadecane could be a more suitable agent for the surface modification with a thermal agent.

Besides the decreases in the surface areas, the filtration times are also an evaluation criterion for the success of the modification process. The hydrophilic halloysite mineral acquires the hydrophobic character owing to the agents adhering to the surface. In the modification process performed in an aqueous medium, the filtration times for the hydrophobic modified halloysite are expected to be shorter than the filtration time for the starting mineral. In the trials performed with different octadecane quantities, no difference providing superiority of one quantity over the others was observed in the filtration times. The results of variation in the interlayer space values when using octadecane are given in Figure 31. When the XRD graph in the figure was examined, the peaks of 10 A, one of the characteristic peaks of halloysite, were observed to disappear as a result of heat treatment. The peaks of 7 A, another characteristic peak, expanded to 7,56-7,66 A. While the quantity of octadecane is insufficient to increase the interlayer space value in the trials performed with the addition of 1%, 2,5% and 5% octadecane, it is considered that the quantity of the agent penetrating the structure increases in parallel with the increase in the quantity of the agent and thus raises the 7 A peak to the level of 15,21 A in the trials performed with the addition of 10% agent.

This morphological study was performed for the samples with 1% thermal agent content, as was the case with SEM. The starting halloysite mineral has a length of about 1,2 microns, an outer diameter of 40 nm and an inner diameter of 20 nm. The change in the tubes compared to this starting halloysite was examined.

The morphological images (TEM) following the addition of 1% PEG 600 are shown in Figure

32. The tube length of halloysite modified by the use of 1% PEG 600 is around 200-400 nm. The tubes were observed to break and became shorter than the starting mineral. The average outer diameter is 82 nm and inner diameter is 41 nm. Considering the outer diameter of 40 nm and inner diameter of 20 nm of the starting mineral, the nanotube width of halloysite approximately doubled. This expansion also supports the XRD graphs.

The morphological images (TEM) following the addition of 1% PEG 1000 are shown in Figure

33. An examination of the TEM results of the trial performed with the addition of 1% PEG 1000 revealed that the tubes became shorter as compared to the purified halloysite and that their lengths varied between 200 and 600 nm. This shortening could be caused by the mechanical stirring of the sample throughout the modification process. The outer diameter was measured about 70 nm and the inner diameter was measured about 30 nm. Comparing these values with the properties of the starting mineral, an increase by about 50% is present.

The morphological images (TEM) following the addition of 1% eicosane are shown in Figure

34. The tubes broke as a result of the modification by the addition of 1% eicosane, as in the modifications with the other thermal agents, and the tube lengths varied in the range of 200-300 nm. As for the outer diameter of the tubes, the value is around 50 nm and an increase of 25% is present relative to the purified halloysite. On the contrary, the inner diameter is around 10 nm and decreased by 50% compared to the starting mineral.

The morphological image (SEM) following the addition of 1% octadecane is shown in Figure 35, the morphological image (SEM) following the addition of 10% octadecane is shown in Figure 36, the morphological image (TEM) following the addition of 1% octadecane is shown in Figure 37, and the morphological image (TEM) following the addition of 10% octadecane is shown in Figure 38.

The tubes broke as a result of the modification by the addition of 1% octadecane, as in the modifications with the other thermal agents, and the tube lengths varied in the range of 200-600 nm. As for the outer diameter of the tubes, the value is around 50 nm; the inner diameter is around 15-20 nm and similar to the starting mineral. When the difference between the addition of 1% and 10% octadecane was examined, the diameter increases were observed although there was no change in the tube lengths. In the sample with the addition of 10% thermal agent, the outer diameter increased to 60 nm and the inner diameter increased to 20-25 nm. This is an indication of the increase in the diameters and the increase in the interlayer space when more agent is introduced to the tubes. This result is consistent with the values of d obtained in XRD.

Table 20. Comparison of the diameter and length values following the modification with the addition of the thermal agent at 1%, based on TEM results When the SEM and TEM results are evaluated collectively for all the thermal agents, the length of the tubes decreased as compared to that of the starting mineral. It is believed that the performance of the stirring with a mechanical mixer during the modification caused the tubes to break. Increases were observed in the diameters of the halloysite nanotubes as a result of the surface modification with all thermal agents. This increase was considered to be caused by the thermal agent molecules adhering to the surface. The decrease in the surface areas as revealed by BET and the shifting of the halloysite peak of 10 A to 15 A as revealed by XRD support this conclusion.

Modification with benzotriazole:

In a preferred embodiment of the invention, halloysites are enabled to be modified with anticorrosive agents, preferably benzotriazole (C6H5N3). The anticorrosive action may be achieved following the modification with benzotriazole.

The method employed for the production of halloysite modified with benzotriazole is as follows:

• feeding, in wet or dry state, halloysite with a solid concentration of preferably 5-15%,

• mixing halloysite and 1-15% by weight anticorrosive agent for 45-95 minutes at a temperature of 50-80°C,

• cooling the mixture at room temperature,

• adding methanol or ether to the mixture and stirring for 5-15 minutes,

• filtering the mixture, and

• drying at a temperature of 50-75°C.

While the process of modifying halloysite with benzotriazole may be performed under a pressure of 1,5-2, 5 bars, it is also possible to realize the process without applying extra pressure. The filtration process is performed preferably in a filter press or by way of holding and draining.

The drying process is performed preferably in a fan drying oven or a vacuum drying oven or using microwave. The drying in a fan drying oven and in a vacuum drying oven is realized for 12-24 hours at a maximum temperature of 60-70°C, while the drying by the use of microwave is performed for 5-70 minutes.

Modification with silanized quaternary salt:

In a preferred embodiment of the invention, halloysites are enabled to be modified with silanized quaternary salt. In a preferred embodiment of the invention, silanized quaternary salt is an organosilane quaternary amine product. The antimicrobial action may be achieved following the modification of halloysites with silanized quaternary salt.

The method employed for the production of halloysite modified with silanized quaternary salt is as follows:

• feeding, in wet or dry state, halloysite with a solid concentration of preferably 5-15%,

• mixing halloysite and 1-15% by weight silanized quaternary salt for 45-95 minutes at a temperature of 50-80°C,

• cooling the mixture at room temperature,

• adding methanol or ether to the mixture and stirring for 5-15 minutes,

• filtering the mixture, and

• drying at a temperature of 50-75°C.

While the process of modifying halloysite with silanized quaternary salt may be performed under a pressure of 1,5-2, 5 bars, it is also possible to realize the process without applying extra pressure. The filtration process is performed preferably in a filter press or by way of holding and draining.

The drying process is performed preferably in a fan drying oven or a vacuum drying oven or using microwave. The drying in a fan drying oven and in a vacuum drying oven is realized for 12-24 hours at a maximum temperature of 60-70°C, while the drying by the use of microwave is performed for 5-70 minutes.

As described above in detail and as presented in the numerous analysis results, it is possible to perform the modification of halloysites both via the surface and via the tube interior as well as via between the layers by employing the methods also described above, and it is possible to provide functionalities by using different silanes, quaternary ammonium salts, mixtures thereof, phase shifter chemicals like ethylene glycol derivatives and octadecane, benzotriazole and silanized quaternary salts, according to the nature of the functional additive desired. The results such as antimicrobial action, anticorrosive action, thermal improvement, strength increase and impact resistance improvement are observed in the product where such agents are added. The halloysites modified with quaternary ammonium salts and/or silanes may be used in the automotive and cable industries for a surface compatible with PP (polypropylene) and PE (polyethylene), the halloysites modified with thermal agents may be used for the acrylic fiber (polyacrylonitrile) applications, the halloysites modified with anticorrosive agents may be used in the paint and marine applications, and the halloysites modified with silanized quaternary salts may be used in every field where antimicrobial action is desired.