A COST-EFFECTIVE IMPACT RESISTANCE-INCREASING HYBRID COMPOSITE

MATERIAL AND A PRODUCTION METHOD THEREOF

Field of Invention

The present invention relates to a hybrid composite material suitable for use as additive to increase the impact resistance of rigid plastic products, as well as a production method of said material.

Prior Art

It has been aimed to increase the strength of rigid plastic materials, particularly like PVC polymers, as well as thermoplastic polyesters, nylon, polyolefins, polystyrene, polymethylmethacrylate polymers, by adding various standard polymer powders in certain amounts to impart impact resistance. Materials for increasing the impact-resistance (impact modifiers) can be exemplified with methacrylate-butadiene-styrene (MBS) copolymers, acrylonitrile-butadiene-styrene (ABS) copolymers, acrylic core-shell (AIM) polymers and chlorinated polyethylenes. The purpose of these materials is to disperse the energy resulting from an impact within the PVC matrix so that absorption is achieved. Nowadays, improvements are being made in such materials imparting impact resistance such that they provide a more efficient absorption process and the costs incurred during their production processes are reduced.

According to the patent document US8378013, mineral fillers/materials, together with another acrylic polymeric material, used as an adhesive, are admixed with a standard acrylic-based impact resistance-increasing polymer material in an aqueous medium, and the resulting mixture is dried in spray driers. During the drying process, the integration of the mineral fillers to the standard acrylic-based impact resistance-increasing polymer takes place according to the adhesion principle without the aid of any coupling agent. The standard acrylic-based impact resistance-increasing material is produced in a core-shell form according to the emulsion polymerization method described above so as to yield a latex product. The mineral filler in the form of powder, i.e. calcium carbonate, is mixed with a water-soluble sodium polyacrylate solution, which will function as an adhesive in the next drying period, to give a slurry. Then, the slurry is introduced into the latex product obtained in the previous step and the resulting mixture of slurry and latex is dried in spray driers according to known methods. During the drying process, the mineral filler, calcium carbonate, becomes adhered to the standard acrylic-based impact resistance-increasing polymer so that their assembly is completed.

In general, the addition of the mineral filler to the standard impact resistance-increasing material can only be made in limited amounts/rates because of the fact that segregation, solid-solid separation take place, powdery materials are spread around in the working environment as they are introduced, and that significant errors occur in formulations because of separation. Said limited amount cannot exceed 4-5%.

Accordingly, besides the standard impact resistance-increasing materials according to the prior art, a need has arisen for developing a novel material wherein a mineral filler can be added in an amount of up to 60%. Thus, the present invention provides a quality and homogenous material, wherein 10% to 60% of a mineral filler can be added to the main material and thus the costs are reduced, and wherein no unfavorable circumstances take place such as segregation, solid-solid separation, and wherein no powdery materials are spread around in the working environment as they are introduced.

Brief Description of Invention

The present invention relates to producing a hybrid composite material which provides impact resistance, comprising the binding of an acrylic polymer in emulsion form with an inorganic mineral used as a filler by means of a coupling agent. During the binding process, the coupling agent, which is an organo-inorganic complex, serves as a bridge between the organic polymer and the inorganic filler. The coupling agent forms a molecular layer over the filler and thus, on one side, binds to polymer chains by means of surface-energy modifications and chain entanglement, and on the other side, based on its proton-reactivity, binds to the inorganic minerals via covalent bonds with the protons presented on the surface of the mineral, so that the coupling agent builds a chemical bridge between and associates the two types of materials of different origins, one organic and the other inorganic. The method of producing a hybrid composite material according to the present invention comprises the steps of mixing at least one inorganic mineral filler in the form of dry powder together with an acrylic polymer in the form of an emulsion and a coupling agent in a stirring vessel; transferring the mixture obtained in the stirring vessel to a drying medium wherein a hot air is present, atomizing the mixture transferred to said drying medium by means of an atomizer disposed on an upper side of the medium and spraying it into the hot air stream, so that the polymer in an emulsion form in the drying medium is dried and bond with the inorganic mineral filler to give a hybrid material in a powder form. The hybrid composite material according to the present invention is a cost-effective product, capable of increasing the impact resistance of rigid PVC product applications such as profiles, pipes and siding for cladding of exterior walls of buildings, , as well as of plastic-based polymers like thermoplastic polyesters, nylons, polyolefins, polystyrene, polymethacrylate.

Brief Description of Figures

Figure 1 shows scanning electron microscopy (SEM) images of hybrid composite materials according to the present invention.

Figure 2 provides a flowchart of the steps of mixing a mineral filler with an acrylic polymer emulsion in the presence of a coupling agent, supplying the resulting mixture to a spray drier, and of the binding process which takes place in the spray drier. Figure 3 shows the binding taking place between the coupling agent and the inorganic mineral filler by means of proton coordination.

Figure 4 shows a molecular layer of the coupling agent with a thickness of 1.5 nm over a particle of the inorganic mineral filler.

Figure 5 shows scanning electron microscopy (SEM) images of hybrid composite materials produced by mixing calcium carbonate powder with a standard acrylic-based impact resistance-imparting powder polymer, wherein no coupling agent is used. Figure 6 shows scanning electron microscopy (SEM) images of a product made from a standard acrylic-based impact resistance-imparting polymer material, comprising no filler.

The reference numbers used in the figures are as below:

(1) Coupling agent

(2) Inorganic mineral filler

(3) Hybrid composite material

(4) Acrylic polymer

(5) Stirring vessel

(6) Drying medium

(7) Atomizer

(8) Pump

(9) Supply tank

(10) Hot air supply channel

(1 1) Lower reservoir of the drying medium

(12) Supply pipe

(13) Small cyclone silo

(14) Discharge pipe

Object of Invention

The object of the present invention is to develop a hybrid composite material suitable for increasing the impact resistance of rigid PVC applications like profiles, pipes and siding for cladding of the exterior walls of buildings, as well as of plastic-based polymers like thermoplastic polyesters, nylons, polyolefins, polystyrene, polymethacrylate.

Another object of the present invention is to develop a low-cost hybrid composite material, wherein 10% to 60% of a mineral filler can be added to the main material by means of a coupling agent to increase the impact resistance of rigid polymers.

A further object of the present invention is to develop a material with an increased shelf life produced to contain homogeneous particles, which do not show any segregation, disintegration, decomposition during use by binding an amount of 10% to 60% of an inorganic mineral filler to an acrylic polymer. Still a further object of the present invention is to use the hybrid material in the form of dry powder according to the present invention as an additive for increasing the impact resistance in siding applications, PVC window profile applications, as well as in other rigid PVC applications.

Description of Invention

The strength of rigid plastic materials, particularly of PVC polymers are increased by using agents which provide impact resistance. By virtue of these agents, the energy resulting from an impact is dispersed within the matrix of the rigid plastic material and transferred. Regular impact resistance-increasing agents are supplemented with mineral fillers to reduce the costs. However, the supplementation of a regular impact resistance-increasing agent with an inorganic mineral filler in the products developed for this purpose cannot be above 4-5% without the use of a mediating agent.

For this reason, a hybrid composite material (3) is developed according to the present invention, wherein an inorganic mineral filler (2) is added to the main material by means of a coupling agent (1) to increase the impact resistance of rigid polymers.

The hybrid composite material (3) according to the present invention, which is suitable for use as an impact resistance-increasing agent and of which a representative SEM image is given in Figure 1 , comprises at least one acrylic polymer (4), at least one inorganic mineral (2) as a filling agent in the form of dry powder, and at least one coupling agent (1), which, on the one side, binds to polymer chains of the acrylic polymer (4) by means of surface energy modifications, and on the other side, to said inorganic minerals (2) by means of covalent bonding. The method of producing the hybrid composite material (3) according to the present invention comprises the steps of mixing at least one inorganic mineral filler (2) in the form of dry powder, together with an acrylic polymer (4) in the form of an emulsion and a coupling agent (1) in a stirring vessel (5); transferring the mixture obtained in the stirring vessel (5) to a drying medium (6) wherein a hot air stream is provided, atomizing the mixture transferred to said drying medium (6) by means of an atomizer (7) disposed on an upper side of the medium and spraying it into the hot air stream, so that the acrylic polymer (4) in an emulsion form in the drying medium (6) is dried and bond with the inorganic mineral filler (2) to give a hybrid composite material (3) in a powder form.

In an exemplary embodiment according to the present invention, the acrylic polymer (4) used is produced in two steps, wherein it is dispersed in an aqueous medium and is subjected to an emulsion polymerization method according to the known core-shell principle. Acrylic polymer (4), the polymers of which are prepared according to emulsion polymerization, is a product which is almost 100% organic, made of entirely organic input materials.

In another exemplary embodiment according to the present invention, the combination of the inorganic mineral filler (2) with the impact resistance-increasing acrylic polymer (4), which is almost 100% organic emulsion, is made in the spray drier (6), where they are dried together with the coupling agent (1).

According to the detailed flowchart given in Figure 2, the mixture obtained in the stirring vessel (5) is supplied to a supply tank (9) by means of a pump (8). The mixture is supplied in batches from the supply tank to the drying medium (6). Hot air is fed into the drying medium (6) by means of a supply channel (10). The most important unit in such a drying medium (6) is the atomizer (7). The atomizer (7) is such a device that disintegrates a liquid to be dried into very small particles each with a diameter of 50 to 500 μηι depending on various factors. The mixture to be dried is separated into tiny particles in the atomizer (7) and then sprayed into a hot air stream. The mixture separated from the water phase under cycloidal air flow is turned into solid particles and advanced in the form of a hybrid composite product (3), which is separated from the gas stream in the cyclone and delivered to the lower reservoir (11) of the drying means. The humid air generated is conveyed to a smaller silo (13) by means of a pipe (12) providing interconnection with the drying medium (6) and is fed to the exterior through an discharge pipe (14) connected to the silo (13). During this process, some amount of the hybrid composite material (3) entrained with humid air is collected under the silo (13) and fed back into the cyclone system.

In an exemplary embodiment according to the present invention, the coupling agent (1) forms an atomic layer on the inorganic mineral filler (2) and coordinates with free surface protons on the inorganic mineral filler (2) to provide the necessary binding. Figure 4 illustrates the binding of the coupling agent (1) to the inorganic mineral filler (2) by means of proton coordination. Thus, the coupling agent (1) binds to the inorganic mineral filler (2) by forming an organic monomolecular layer, without generating any side products or condensates.

In an exemplary embodiment of the present invention, a titanium-derived coupling agent (1) binds to and associates with the inorganic mineral filler (2) according to the following mechanism:

The coupling agent (1) general formula and the filler (2) may symbolically be considered as following ; (Y-R-X-0-) ₃ -Ti-OR' (1) + M O H (2)

In an exemplary embodiment of the present invention, a [OR'] residue on titanate coordinates with and accordingly binds to the protons on the inorganic mineral filler (2) [M]. The X residue, in turn, with its probable alkyl, carboxyl, sulfonyl, phosphate, pyrophosphate structure, gets entangled in composite structure, whereas the R residue, with its aliphatic or aromatic long chain structure, gets entangled in between the polymer chains so to provide van der Waals compatibilization. Preferably, the Y residue comprises an extension that bears an acrylic, methacrylic, or an amino functional group.

In an exemplary embodiment of the present invention, the coupling agent (1) forms a monomolecular layer thinner than 1.5 nm on the inorganic mineral filler (2). Figure 4 shows a 1.5 nm thick molecular layer of the coupling agent (1) over one particle of the inorganic mineral filler (2).

In an exemplary embodiment according to the present invention, the other end of the coupling agent (1) bound to the filler is entangled with the polymer chains of the acrylic polymer (4) in an emulsion form by surface energy modifications, thereby binding to the polymer phase in a rapid manner.

In another exemplary embodiment according to the present invention, the coupling agent (1), which is hydrophobic, is emulsified with nonionic surface active agents in order to let it homogeneously disperse within the aqueous acrylic polymer emulsion (4) and reach the polymer chains.

Preferably, the nonionic surface active agent is selected from nonylphenols or ethoxylated nonylphenols (ENP).

In another exemplary embodiment according to the present invention, 1 part of coupling agent (1) is mixed with 1 part of ENP to give a 50% solution of the coupling agent. The amount of the coupling agent (1) to be used in the process is calculated according to the amount of the inorganic mineral filler (2). The amount of the coupling agent (1) is 0.1 % to 1.5% of the amount of inorganic mineral filler (2). It is preferably used in an amount from 0.25% to 0.75%. In a preferred embodiment according to the present invention, the acrylic polymers (4) are selected from acrylic-based impact resistance-increasing agents and preferably are one of methacrylate-butadiene-styrene (MBS) copolymers and acrylonitrile-butadiene-styrene (ABS) copolymers. In an embodiment according to the present invention, the acrylic polymer is added to the mixture in an amount of 40-90% by mass.

In another embodiment according to the present invention, the inorganic mineral filler (2) is selected from calcium carbonate and preferably is carbon black, clay minerals of the montmorillonite group, zeolite, perlite, calcium carbonate (calcite); precipitated calcium carbonate, ground calcium carbonate, nano-sized calcium carbonate or hydrotalcite. In an embodiment according to the present invention, the inorganic mineral filler is added to the mixture in an amount of 10-60% by mass.

In an exemplary embodiment according to the present invention, the inorganic mineral filler (2) is bond to the acrylic polymer (4) using a titanium-based coupling agent (1), but organo-titanate, zirconate or aluminate compounds can also be used for this purpose. An exemplary embodiment uses neopentyl diallyloxy tris-(dioctylpyrophosphate)-titanate.

Exemplary Embodiment: In an exemplary embodiment according to the present invention, the acrylic polymer (4) used was an emulsion of a standard impact resistance-increasing acrylic product of the firm Akdeniz Kimya, product reference DMA 660, comprising 43% polymer solid substance. Since the target product will contain the mineral filler, calcium carbonate, in an amount of 30% thereof, the mineral filler is added in an amount to give a 30% mineral filler content in the final product based on the solid substance content of the acrylic emulsion.

In an exemplary embodiment according to the present invention, to a 500 kg emulsion containing 215 kg of 43% acrylic polymer is added 92 kg of mineral filler, calcite, so that the target product contains 30% of calcite.

In an exemplary embodiment according to the present invention, the amount of the coupling agent used was 0.6% of the amount of mineral filler and thus 1.1 kg of an ENP 50% solution, an emulsified form of the coupling agent, was added.

Up to 30% water is added to the emulsion of acrylic polymer (4) in the composition which provides the standard impact resistance and contains the acrylic polymer- to be combined with the mineral filler, so that 650 kg of an aqueous emulsion is obtained. The coupling agent (1) emulsified to make it compatible with the aqueous medium is added to said aqueous emulsion and stirred for 15 minutes. According to the proportion in the final product composition, a predetermined amount of the inorganic mineral filler powder (2) is added in batches to this mixture and then stirred for 30 more minutes.

Then, the mixture is fed to a supply tank (9) by means of a pump (8). The mixture reaching the supply tank (9) is then passed in batches to an atomizer (7) disposed on an upper side of a drying medium (6) in free flow based on the difference of elevations. The mixture is atomized by means of the atomizer (7) on the top of the drying medium (6) and sprayed into a silo. The drying medium (6) is such a medium into which hot air is fed at 170°C through a supply channel (10). The mixture pulverized in the atomizer is exposed to the hot air stream at 170°C, so that the mixture instantly starts to lose its water content. Meanwhile, the inorganic mineral filler (2) and the standard impact resistance-increasing polymer (4) in the pulverized mixture are bond together by means of the coupling agent (1) as they travel downwards in the drying silo of which the temperature starts at the top from 170°C and gradually decreases to 70-80°C towards the middle. The powder-form hybrid composite material (3) leaving the air stream in the conical lower reservoir (1 1) of the drying silo becomes dried and then collected in the lower reservoir (1 1) of the silo. The steam released from the mixture is conveyed to a smaller cyclone silo (13) by means of a pipe (12) providing interconnection with the drying medium (6) and the humid air is fed to the exterior through an discharge pipe (14) connected thereto. During this process, some amount of the hybrid composite material (3) entrained with humid air is collected under the cyclone silo (13) and fed back into the cyclone system.

As can be seen in Figure 1 , by virtue of the smooth profile generated by the mineral filler and the polymer particles in the product containing 30% of mineral filler, two substances with different structures, i.e. an inorganic material and a polymer, are shown in a single homogenous substance structure without any signs of segregation or dissociation.

Standard acrylic polymer powder is physically mixed with 30% calcite without giving place to any reactions in proportions according to the exemplary embodiment of the present invention. Referring to the electron microscopy (SEM) images in Figure 5, the inorganic portion and the polymer particles can be seen separately. Dispersed dusty and dull rough appearances on and around the polymer particles show the mineral filler calcium carbonate, giving no appearance of a single uniform material. Figure 6, in turn, gives an SEM image of a product produced from acrylic polymer, not containing any mineral filler.

By virtue of the compact form of the hybrid material according to the present invention, it is made possible here to produce a polymer-inorganic composite material, which does not show segregation and disintegration.

The material obtained by the method according to the present invention is used as an impact-resistance increasing plastic additive by being added to rigid PVC, profiles, siding, pipes and similar products at certain proportions, preferably in amounts of 2-10%.

Additionally, impact resistance tests were performed to compare values of the products produced according to the present invention to some known reference products containing no fillers. A comparative Charpy impact test according to EN ISO 179 was conducted on a hybrid composite reinforced window profile comprising filler, the test results being shown in Table 1. The minimum/maximum and standard deviation values given in Table 1 are the resulting values of ten tests performed under laboratory conditions.

A Gardner dart impact test according to ASTM D4226 and ASTM D5420 was performed on a hybrid composite reinforced window profile comprising filler, the test results being shown in Table 2.

The products indicated with Reference 1 and Reference 2 as used in both impact tests are commercially-available standard impact resistance-increasing acrylic materials not containing an inorganic mineral filler.

The levels of breaking behavior of the indicated products according to the impact test method with varying heights were determined and are shown in Table 3.

Test Minimum (kJ/m2) Maximum Mean Standard deviation product (kJ/m2) (kJ/m2)

Reference 57.9 65.6 61.4 1.9

1

Reference 59.4 63.4 60.7 1.3

2

Invention 57.7 63.6 60.4 1.7

Table 1. Resu ts of the Charpy Impact Experiment

Test Mean Expected Mean breaking Normalized mean product breaking standard energy (Joule) breaking energy height (cm) deviation (cm) (cm)

Reference 1 53 4.2 191 692

Reference 2 51.4 3.4 185 680

Invention 55.5 5.4 200 734

Table 2. Resu ts of the Gardner Impact Experiment

Test product Level 1 Level 2 Level 3 Level 4 Level 5

Reference 1 4 5 0 1 0

Reference 2 2 2 0 5 2

Invention 3 1 0 3 3 Table 3. Levels of Breaking Behavior of Samples according to the Impact Test Method with Varying Heights

Accordingly, it can be seen that the test values of the hybrid composite product with a filler according to the present invention are comparable with those products containing no filler and, even that the subject product comprises a filler, that the values obtained were almost at the same levels / values with those products without a filler. Thus, the polymer proportion within the product can be reduced without compromising the original product specifications to give an economical product.