ASBESTOS FREE NANO-HYBRID FOR FIBER-CEMENT COMPOSITE

APPLICATIONS

BACKGROUND

Generally, it is desired to minimize or eliminate the use of asbestos fibers in various applications due to the health risk associated with the use of asbestos fiber related products. However, attempts to minimize or eliminate the use of asbestos fibers in fiber-cement composite applications have met major challenges such as matching the unique characteristic features associated with asbestos related composites such as high tensile strength, good dispersion and high compatibility with Portland cement.

In the last few years, an increase in interest has been given to the use of cellulose fibers as alternatives for conventional reinforcements in cement composites. The development of commercially viable environmentally friendly and healthy materials based on natural resources is on the rise. In this sense, cellulosic fibers as reinforcements for cement composites constitute a very interesting option for the construction industry.

Even though cellulose fiber reinforced cement composites have been introduced, there are still plenty of drawbacks in both mechanical and physical properties observed. The decrease of mechanical properties, such as flexural strength (bending strength) is mainly due to the incompatibility between inorganic - organic interfaces. Furthermore, cellulose fiber reinforced cement materials have performance drawbacks in their physical properties such as lower resistance to water induced damage, higher water permeability, and higher water migration ability (also known as wicking) compared to asbestos cement composite materials. These drawbacks are largely due to the presence of water conducting channels and voids in the cellulose fiber lumens and cell walls. As such, conventional cellulose fibers can cause the material to have a higher saturated mass, poor wet to dry dimensional stability, lower saturated strength, and decreased resistance to water damage.

BRIEF SUMMARY

As noted above, in the last few decades there has been an upsurge in interest in industrial countries to replace asbestos fibers with alternative fiber sources. This has led to a plethora of scientific discoveries which has steered scientific community towards the use of cellulose fibers as an alternative source in fiber-cement composites. However, the incompatibility between inorganic- organic interface in the cement matrix and cellulose fiber surface causes a decrease in mechanical strength as well as performance drawbacks in physical properties of the fiber-cement composites.

Various embodiments provide solutions to the issues related to both mechanical and physical properties of fiber-cement composites that are free of asbestos. For example, various embodiments provide fiber reinforced cement composites that include cellulose fibers that have been modified prior to application in fiber reinforced cement composites. For example, nano-hybrid cellulose fibers may be generated via surface modification of cellulose fibers with hydroxyapatite (HA) nanoparticles prior to application of the modified cellulose fibers in fiber reinforced cement composites. Various embodiments provide methods, apparatus, systems, and/or the like for performing the surface modification of cellulose fibers with HA nanoparticles. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) studies revealed the successful synthesis, via an example embodiment, of rod shaped HA nanoparticles by co precipitation technique with a homogeneous size distribution (diameter < 50 nm, length -100-200 nm). Powder x-ray diffraction (PXRD) confirmed the formation, via an example embodiment, of HA in pure crystalline form. High-resolution transmission electron microscopy (HRTEM) and fast Fourier transform (FFT) pattern further described the poly crystalline nature of the HA nanoparticles, synthesized via an example embodiment. Cellulose fibers were surface modified, via an example embodiment, with HA nanoparticles at pH - 7.8. Fourier-transform infrared spectroscopy (FUR) of HA nanoparticles coated cellulose fibers confirmed chemical bonding interactions, in an example embodiment, between the two substrates via H-bonding and hence, HA nanoparticles were selected as the candidate for surface modification of cellulose fibers. Various embodiments provide HA nanoparticles coated cellulose fiber reinforced cement composites using the vacuum dewatering technique. In various embodiments, ordinary Portland cement was used for the preparation of fiber reinforced cement composites. It was clearly observed that the applications of HA nanoparticles loaded cellulose fibers in fiber reinforced cement composites materials desirably improved the mechanical and physical properties, in various embodiments. Cellulose fiber reinforced cement sheet produced, according to an example embodiment, using HA nanoparticle coated cellulose fibers with 1 : 1 : 10 ratios (weight) between cellulose, HA nanoparticles, and cement have showed improved bending strength, lower water penetration rate, reduced water absorption and low density.

Various embodiments address the issues related to both mechanical and physical properties of the cellulose fiber reinforced cement composites via a surface treatment of cellulose fibers using nanoparticles. In an example embodiment, hydroxyapatite nanoparticle suspension with a homogeneous size distribution (diameter less than 50 nm and length between 100 - 200 nm) was successfully synthesized by the co-precipitation technique and the delignified cellulose fibers were coated with said nanoparticles at pH ~ 7.8. Various characterization techniques were used to examine the chemical bonding interactions between the fibers and nanoparticles. In attempts to perform the surface modification of cellulose fibers with calcium silicate nanoparticles chemical interactions with the cellulose fibers were not observed.

In various embodiments hydroxyapatite nanoparticles coated cellulose fiber reinforced cement composites are provided that exhibit improved physical and mechanical properties compared to unmodified cellulose fiber reinforced cement composites and also the asbestos fiber reinforced cement composites prepared under the laboratory conditions. All fiber reinforced cement composites were prepared using a vacuum dewatering technique. An example embodiment uses ordinary Portland Cement (OPC) in the preparation of the fiber reinforced cement composites.

Various embodiments provide a fiber reinforced cement composite and/or object made from fiber reinforced cement composite. The fiber reinforced cement composite and/or object made from fiber reinforced cement composite comprises surface modified cellulose fibers, wherein the surface modified cellulose fibers are cellulose fibers coated with hydroxyapatite nanoparticles; and cement. In various embodiments, the fiber reinforced cement composite object is manufactured by surface modifying cellulose fibers with hydroxyapatite nanoparticles to create surface modified cellulose fibers; mixing the surface modified cellulose fibers with cement to create a fiber cement slurry; and casting the fiber cement slurry to form the fiber reinforced cement composite object.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: Figure 1A provides a schematic diagram of an example vacuum casting box, in accordance with an example embodiment.

Figure IB illustrates an actual setup of a vacuum casting box, in accordance with an example embodiment.

Figure 2A illustrates an example hot press, in accordance with an example embodiment.

Figure 2B illustrates an example stainless steel mold, in accordance with an example

embodiment.

Figure 2C shows example fiber reinforced cement composite sheets obtained after pressing, in accordance with an example embodiment.

Figure 3A shows a schematic diagram of an apparatus used for testing the bending strength of fiber reinforced cement sheets, in accordance with an example embodiment.

Figure 3B illustrates dimensions of a three point loading system and test specimen, in accordance with an example embodiment.

Figure 3C illustrates the modified tensile tester used to measure the bending strength of fiber reinforced cement sheets, in accordance with an example embodiment.

Figure 4A illustrates an experimental setup equipped with AutoLab to measure water penetration through a sheet of fiber reinforced cement composite, in accordance with an example embodiment.

Figure 4B is a schematic diagram of the column of the experimental setup shown in Figure 4A that was connected to AutoLab, in accordance with an example embodiment.

Figure 5 provides a plot showing the variation of current with time due to the water penetration through a fiber reinforced cement composite sheet of an example embodiment.

Figure 6 provides a schematic diagram of a Lee’s apparatus for measuring the thermal conductivity of the prepared fiber reinforced cement composite, in accordance with an example embodiment. Figure 7 provides a plot showing the PXRD pattern of HA nanoparticles synthesized in accordance with an example embodiment.

Figure 8 provides an SEM image of HA needle-like nanoparticles obtained via wet chemical precipitation, in accordance with an example embodiment. Figure 9A shows a low resolution TEM image of HA nanoparticles synthesized via an example embodiment.

Figure 9B shows a high resolution TEM image with FFT pattern of HA nanoparticles synthesized via an example embodiment.

Figure 9C shows a zoomed image of the high resolution TEM image shown in Figure 9B. Figure 9D provides a plot showing the intensity profile of HA nanoparticles synthesized via an example embodiment.

Figures 10A, 10B, IOC, and 10D provide plots showing the FTIR spectra for HA nanoparticles synthesized via an example embodiment, for four different wavelength ranges.

Figure 11 provides a plot showing the thermogravimetric analysis (TGA) curve and differential thermogravimetry (DTG) curve of HA nanoparticles synthesized via an example embodiment.

Figure 12A provides an SEM image of delignified cellulose fibers.

Figures 12B, 12C, and 12D provide SEM images of cellulose fibers modified with HA nanoparticles at different zooming levels, according to an example embodiment.

Figure 13 provides spectral imaging of an HA nanoparticle coated cellulose fiber demonstrating the uniform distribution of elements such as Ca, P, and O, present in HA nanoparticles completely coating the fiber surface, according to an example embodiment.

Figure 14 provides plots showing the Electron Energy Loss Spectroscopy (EELS) analysis of the HA nanoparticle coated cellulose fibers after multiple washing cycles, according to an example embodiment. Figure 15 provides a plot showing the PXRD patterns of (a) cellulose fibers coated with HA nanoparticles, (b) HA nanoparticles and (c) cellulose fibers, according to an example embodiment.

Figure 16 provides a plot showing an FHR spectrum of a debgnified cellulose fiber.

Figure 17 provides a plot showing FTIR spectra of (a) HA nanoparticles, (b) cellulose fibers coated with 0.05 M HA nanoparticles and (c) cellulose fibers, according to an example embodiment.

Figure 18 provides two plots showing the peak shifts in the spectra of a) HA nanoparticles; (b) cellulose fibers coated with 0.05 M HA nanoparticles and (c) cellulose fibers, according to an example embodiment.

Figure 19 provides a diagram illustrating a possible mechanism for the interaction between cellulose fibers and HA nanoparticles, according to an example embodiment.

Figure 20 provides a plot showing TGA thermograms of (a) debgnified cellulose fibers, (b) cellulose fibers coated with 0.05 M HA nanoparticles and (c) HA nanoparticles, according to an example embodiment, with an inset plot showing DTG curves of (a) debgnified cellulose fibers and (b) cellulose fiber coated with 0.5 M HA nanoparticles, according to an example

embodiment.

Figure 21 provides a plot showing the effect of agitation time on the extent of coating of the cellulose fiber by the HA nanoparticles, according to an example embodiment.

Figures 22A, 22B, 22C, and 22D provides SEM images of cellulose fibers coated with 0.05 M (Figure 22A), 0.025 M (Figure 22B), 0.0125 M (Figure 22C), and 0.00625 M (Figure 22D) HA nanoparticles, in accordance with an example embodiment.

Figure 23 provides a plot showing TGA thermograms of (a) cellulose fibers, cellulose fibers coated with (b) 0.00625M, (c) 0.0125M, (d) 0.025M and (e) 0.05 M HA nanoparticles, according to an example embodiment. Figure 24 provides a plot showing a correlation between the initial concentrations of HA nanoparticles and the extent of coating, according to an example embodiment.

Figure 25 provides a plot showing FTIR spectra of cellulose fibers coated with (a) 0.05M, (b) 0.025M, (c) 0.0125M and (d) 0.00625M HA nanoparticles and (e) uncoated cellulose fibers, according to an example embodiment.

Figure 26 provides two plots showing FTIR spectra (selected wavenumber range) of cellulose coated with (a) 0.05M, (b) 0.025M, (c) 0.0125M and (d) 0.00625M HA nanoparticles and (e) uncoated cellulose fibers, according to an example embodiment.

Figure 27 shows example fiber reinforced cement composite sheets produced using laboratory scale vacuum dewatering technique, according to an example embodiment.

Figure 28 provides a plot showing the thickness of the HA nanoparticles coated and uncoated cellulose fiber reinforced cement sheets, according to an example embodiment.

Figure 29 provides a plot showing the density of the HA nanoparticles coated and uncoated cellulose fiber reinforced cement sheets, according to an example embodiment. Figure 30 provides a plot showing the bending strength of HA nanoparticles coated and uncoated cellulose fiber reinforced cement sheets, according to an example embodiment.

Figure 31 provides a plot showing the percentage water absorption of the HA nanoparticles coated and uncoated cellulose fiber reinforced cement sheet, according to an example embodiment. Figure 32 provides a plot showing the rate of water penetration of the HA nanoparticle coated and uncoated cellulose fiber reinforced cement sheets, according to an example embodiment.

Figure 33 provides a plot showing the thermal conductivity of the HA nanoparticles coated and uncoated cellulose fiber reinforced cement sheets, according to an example embodiment. DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. As used herein, the term approximately refers to refers to tolerances within manufacturing and/or engineering standards.

Various embodiments provide methods, apparatus, systems, and/or the like for generating nano- hybrid cellulose fibers via surface modification of cellulose fibers with hydroxyapatite (HA) nanoparticles. Various embodiments provide a fiber reinforced cement composite comprising cellulose fibers coated in HA nanoparticles (e.g., nano-hybrid cellulose fibers that have had their surfaces modified through coating with HA nanoparticles).

1. Background Various embodiments provide a novel nano-hybrid fibers for fiber reinforced cement composites via the surface modification of delignified cellulose fibers that improve the durability of fiber reinforced cement composites comprising the nano-hybrid fibers.

Even though, cellulose fiber reinforced cement composites have been introduced after much research, still there are plenty of drawbacks in both mechanical and physical properties observed. The decrease of mechanical properties, such as flexural strength (bending strength) is mainly due to the incompatibility between inorganic - organic interfaces. Furthermore, cellulose fiber reinforced cement materials have performance drawbacks in their physical properties such as lower resistance to water induced damage, higher water permeability, and higher water migration ability (also known as wicking) compared to asbestos cement composite materials. As such, conventional cellulose fibers can cause the material to have a higher saturated mass, poor wet to dry dimensional stability, lower saturated strength, and decreased resistance to water damage.

Hydroxyapatite nanoparticle suspension with a homogeneous size distribution (diameter less than 50 nm and length between 100 - 200 nm) was successfully synthesized by the co-precipitation technique and the delignified cellulose fibers were coated with said nanoparticles at pH ~ 7.8 via an example embodiment. Various characterization techniques were used to examine the chemical bonding interactions between the fibers and nanoparticles.

Additionally, various embodiments provide hydroxyapatite nanoparticles coated cellulose fiber reinforced cement composites. The physical and mechanical properties of the hydroxyapatite nanoparticles coated cellulose fiber reinforced cement composites are compared against unmodified cellulose fiber reinforced cement composites and also the asbestos fiber reinforced cement composites prepared under the laboratory conditions. All fiber reinforced cement composites were prepared using a vacuum dewatering technique which has been extensively used in the formation of fiber reinforced cement sheets in lab scale. Ordinary Portland Cement (OPC) is used for the preparation of said fiber reinforced cement composites, in an example embodiment. Also, the physical and mechanical properties of the composites such as density, percentage moisture absorption, water penetration property, thermal conductivity and bending strength were determined and were used to evaluate the physical and mechanical performance of the hydroxyapatite nanoparticles coated cellulose fiber reinforced cement composites over the other fiber reinforced cement composites.

2 Introduction

2.1 Asbestos fiber-cement technology

Asbestos can be identified as a family of naturally occurring hydrated silicates, which is fibrous in nature. The principle varieties of asbestos are chrysotile, which is a serpentine material and anthophyllite, amosite, tremolite and actinolite, which are amphiboles. The ability to be separated into individual fibers, or the structure with one dimension significantly larger than the other two is the major identifying characteristic of this mineralogical group. Asbestos fibers exhibit excellent physical and chemical properties including resistance to thermal and chemical degradation, high tensile strength and durability and specially the ability to bond very strongly with cement. Due to these specific properties, asbestos fibers have been used in a broad variety of industrial applications. Ludwig Hatschek made the first asbestos reinforced cement product about 120 years ago. Since then, for over 100 years, this form of fiber cement found extensive use for roofing products, pipe products, and walling products, both external siding (planks and panels), and wet-area lining boards [3, 9] Due to the great thermal stability of asbestos, the composite of asbestos-cement was also used in a wide range of applications requiring fire resistance. As the high density asbestos- cement composites are of low ^r porosity and permeability, the products made by them were relatively light weight and the water permeability relatively low. These are the great advantages associated with asbestos-cement composites. However, due to health issues associated with asbestos exposure, the use of asbestos has been greatly decreased.

2.2 Cellulose fibers as an alternative fiber source

In the last few years, an increase in interest has been given to the use of cellulose fibers as alternatives for conventional reinforcements in composites. The development of commercially viable environmentally friendly and healthy materials based on natural resources is on the rise. In this sense, cellulosic fibers as reinforcements for cement composites constitute a very interesting option for the construction industry.

2.3 Cellulose fiber reinforced cement composites

According to the literature, pulp is the most common fiber form which has been used to reinforce cementitious matrices. Also, the majority of cellulose pulps in preparation of fiber reinforced cement sheets were obtained chemically by Kraft process. There are several research works reporting for the use of cellulose pulps obtained from both chemical and mechanical pulping in the preparation of fiber reinforced cement sheets with different sources of cellulose fibers. For instance, researchers have successfully evaluated the properties of fiber reinforced cement composites, using eucalyptus pulp, pulps from banana, pinus pulp, sisal fiber which is very cheap and is an abundant crop plant, cotton linters, and agricultural waste.

According to reported works, it was observed that the mechanical behavior of the composite is dependent on the fiber type, diameter, length, texture and the aspect ratio of the fibers. However, the use of pulped fibers in the cementitious matrix facilitates two-dimensional and homogeneous distribution. Furthermore, irrespective of the method, almost all composites showed approximately 8-12 MPa bending strength value for cellulose fiber-cement composites.

2.4 Major drawbacks associated with cellulose fiber reinforced cement composites

Even though, the cellulose fiber reinforced cement composites have been introduced after much research, still there are plenty of drawbacks in both mechanical and physical properties observed. The decrease of mechanical properties, such as flexural strength (bending strength) is mainly due to the incompatibility between inorganic - organic interfaces. In fact, the high alkalinity of water in the pore of the cementitious matrix weakens the cellulose fibers, induces their mineralization and, consequently, yields to the decay of the composite tenacity.

Further, the cellulose fiber reinforced cement materials can have performance drawbacks in their physical properties such as lower resistance to water induced damage, higher water permeability, and higher water migration ability (also known as wicking) compared to asbestos cement composite materials. These drawbacks are largely due to the presence of water conducting channels and voids in the cellulose fiber lumens and cell walls. The pore spaces in the cellulose fibers can become filled with water when the material is submerged or exposed to rain/condensation for an extended period of time. The porosity of cellulose fibers facilitates water transportation throughout the composite materials and can affect the long-term durability and performance of the material in certain environments. As such, conventional cellulose fibers can cause the material to have a higher saturated mass, poor wet to dry dimensional stability, lower saturated strength, and decreased resistance to water damage.

2.5 Preparation of hydroxyapatite nanoparticles

A variety of methods may be used to synthesize hydroxyapatite, including co-precipitation, sol- gel method, emulsion, hydrolysis method, and hydrothermal approach.

1) Co-precipitation method

One method that may be used in various embodiments to synthesize hydroxyapatite and/or for preparation of hydroxyapatite nanoparticles is co-precipitation. This wet chemical method involves an acid base reaction, where a phosphate (PO4 ³ ) ligand reacts with calcium (Ca ²⁺ ) source in the presence of other additives such as pH controllers, surface modifiers, etc. The pH of the medium can range from 3 to 12 and the temperature from room temperature (e.g., 15-25° C) to the boiling point of water (e.g., 100° C).

Two possible reaction for synthesizing HA nanoparticles via the co-precipitation method are shown as Equations 2.1 and 2.2. In various embodiments, the reaction shown by Equation 2.1 is used for synthesizing HA nanoparticles via co-precipitation method.

4 NH4OH

Caio(P04) ₆ (OH) ₂ + 18 H ₂ 0 (2.1)

10 Ca(NC ) ₂ + 6 (NH ) ₂ HPC>4 -► Caio(P04) ₆ (OH) ₂ + 6 H ₂ 0 + 20 NH4NO3 (2.2)

2) Sol-gel method

In an example embodiment, the sol-gel process is used for synthesizing synthesize hydroxyapatite and/or preparing of hydroxyapatite nanoparticles. The sol-gel method is a method for mineralizing from precursors in a solution, preferably organometallic compounds or other suitable precursors. There are three different methods involved in manufacturing sol-gel materials, (i) gelation of colloidal powders, (ii) hypercritical drying and by controlling the hydrolysis and condensation of precursors and (iii) incorporating a drying step at ambient temperature. Since, the sol-gel method offers molecular level mixing of Ca and P precursors, the chemical homogeneity of the resulting HA nanoparticles may be very high compared to other techniques of synthesizing hydroxyapatite. In an example embodiment, HA is prepared using a sol-gel method with triethyl phosphate and calcium nitrate as phosphorus and calcium precursors. Two solvents, water and anhydrous ethanol, may be used as the diluting media for HA sol preparation, in an example embodiment. In another example embodiment, the sol-gel process is used in the preparation of HA using Ca (NC ) ₂ 4H ₂ 0 and P ₂ Os as precursor chemicals.

3) Microemulsion methods

In an example embodiment, the microemulsion method is used to prepare HA having a particle size in the range of nanometers with minimal agglomeration. In an example embodiment, calcium nitrate and phosphoric acid are used as chemical precursors of Ca ²⁺ and PO4 ³ . In various embodiments, for the emulsification process, one or more surfactants are mixed with water. A few non-limiting examples for the one or more surfactants include sodium dodecyl sulphate, polysorbate 80, nonylphenol ether, and cetyltrimethylammonium bromide. In various embodiments, the main parameters to be focused during the emulsion method are the type of surfactant, ratio of aqueous and organic phases, pH and temperature. In an example embodiment, nano crystalline HA is synthesized using the microemulsion technique. In an example embodiment, cyclohexane is used as the oil phase, mixed poly(oxyethylene)-5-nonylphenol ether (NP-5) and poly(oxyethylene)-12-nonylphenol ether (NP-12) is used as the surfactant phase, and a solution of Ca(NC )2 and H3PO4 is used as the aqueous phase to synthesize products that were composed of a surface area of 130 m ² /g and particle size between 30 and 50 nm.

4) Hydrothermal methods

In an example embodiment, a hydrothermal process is used for the synthesis of crystalline HA nanoparticles. The process occurs in a closed environment with a higher temperature and pressure greater than autogenously ambient pressure, in an example embodiment. The reaction is conducted inside an autoclave or a pressure vessel, in an example embodiment. Depending on the pressure and temperature used in various embodiments, the hydrothermal method creates chemical bonds and forms nuclei that ensure a relatively stoichiometric and highly crystalline synthesis of HA. In an example embodiment, fine hydroxyapatite single crystals are synthesized by a hydrothermal method with Ca(OH)2 and CaHP04 2H2O as precursors. In an example embodiment, powders of Ca(OH)2, Ca(H2P04)2 Ή2O and distilled water are heated in a pressurized pot at 109°C for one to three hours, resulting in powders consisting of needle shape crystallized hydroxyapatite, 130-170 nm in length and 15-25 nm in width.

3. Methodology

3.1 Instrumentation

Fourier Transform Infrared Spectroscopy (FTIR)

Samples of various embodiments and/or generated via example embodiments were analyzed for determining the chemical structure and the bonding nature. Bruker Vertex 80 coupled with Ram- FT module (RAM II) Fourier Transform Infrared Spectrophotometer was used to obtain all the spectra in the range between 400 and 4000 cm ¹ . Attenuated Total Reflectance (ATR) technique and IR Microscopy were used to obtain the spectra. Potassium bromide (KBr) beam splitter and RT-DTGS detector were used with a SiC globar sample source. Data were acquired and analyzed by instrumental software, OPUS-6.5 version.

Powder X-ray Diffraction (PXRD)

Powder X-ray diffraction patterns of samples of various embodiments and/or generated via example embodiments were recorded by using Bruker D8 Focus X-ray powder diffractometer. Samples were packed onto a plastic sample holder. Cu K a radiation (l = 0.154nm) was used over a 2 Q range 5-80 ^° with a step size of 0.02“and a step time of 1 second, an operating voltage of 45 kV and a filament current of 40 mA . In this study, all the X-ray diffractograms were acquired by using instrumental software, Diffrac plus PXRD commander, version 2. 6. 1. Data were analyzed using EVA version 15.0.0.0 with the support of International Center Diffraction Data (ICDD) PDF II minitex library version 9.0.133.

Thermogravimetric Analysis (TGA)

TGA thermograms of samples of various embodiments and/or generated via example embodiments were obtained under nitrogen atmosphere using TA Instruments SDTQ600. Nitrogen gas purge flow rate was set as 100 ml / min. Sample (10-15 mg) was filled into an alumina pan and heated from ambient temperature to 1200 °C at a rate of 10 °C / min. Data were acquired by TA Q series, version 5.4.0. Thermograms were analyzed using universal analysis 2000, version 4.5. Optical microscopy

Morphology of the delignified cellulose fibers were analyzed by Olympus BX61 optical microscope, with a resolution of 0.01 pm, in bright field mode with the Olympus DP2-BSW software.

Scanning Electron Microscopy (SEM)

The particle size and the morphology of the synthesized samples of various embodiments and/or generated via example embodiments were analyzed using HITACHI SU6600 Scanning Electron Microscope (20-30 kV). Samples were mounted to an aluminum stub using double sided carbon tape. Excess materials were removed. In order to overcome the charging effect, samples were sputtered by gold using HITACHI, E-1020 Ion Sputter.

Energy Dispersive X-Ray Spectroscopy

Elemental mapping of the uncoated cellulose fibers and coated cellulose fibers of some example embodiments was done by using Energy Dispersive X-Ray (EDX) mode attached to HITACHI SU6600 Scanning Electron Microscope.

Transmission Electron Microscopy (TEM)

A drop of the sample dispersion of various embodiments and/or generated via example embodiments was placed on a holey carbon Cu grid and allowed to dry at room temperature (e.g., 15-25°C). A set of images from lower magnification to high resolution images were obtained by a Jeol 2100 HRTEM with a LaB6 electron gun equipped with a Gatan GIF 963 spectrometer system operating at 200 kV. The diffraction patterns (FFT) were obtained using selected area electron diffraction (SAED) technique.

Electron energy loss spectroscopy (EELS)

EELS spectrum of HA nanoparticles coated cellulose fibers was acquired with an EELS spectrometer (EELS Gatan, Quantum 963, USA) attached to the TEM with the energy resolution of 0.05 eV/ channel in STEM spectral imaging mode. Determination of Crystallinity Index of delignified cellulose fibers

Crystallinity index (Crl) of fiber samples of various embodiments and/or generated via example embodiments was calculated by referring to diffraction intensity of crystalline and amorphous regions using the following empirical equation, (Equation 3.1).

Where hoo is the peak intensity at plane (2 0 0), (2Q = 22.1°), and hm is the minimum intensity at the valley between plane (2 0 0) and (1 1 0), (2Q = 18.7°).

3.2 Surface modification of delignified cellulose fibers with HA nanoparticles

In various embodiments, delignified cellulose fibers (dry mass of approximately 5 g, 8% w/w moisture content) were suspended in water (1000 cm ³ ) at room temperature and disintegrated using mechanical agitator (1000 rpm). The separated fibers were collected by filtration (approximately 80 % w/w moisture content). Hydroxyapatite nanoparticles (approximately 0.05 mol din ³ ) were synthesized using a wet chemical method similar to that described by Kottegoda, N., et al. ,A green slow-release fertilizer composition based on urea-modified hydroxyapatite nanoparticles encapsulated wood. Current Science (Bangalore), 2011. 101(1): p. 73-78, in an example embodiment. A solution of H3PO4 (0.6 mol· dm ³ in 50 cm ³ water) was added drop-wise into a suspension of 1 mol dm ³ calcium hydroxide (3.86 g of Ca(OH)2 in 50 cm ³ water) while stirring at 600 rpm using a magnetic stirrer, in an example embodiment. Ca to P molar ratio was maintained at 1.67. The resulting nano dispersion was further stirred for another approximately 10 minutes. pH of the suspension was measured and it was 7.8. Transmission Electron Microscopic (TEM) imaging was performed soon after the synthesis and PXRD analysis was performed to obtain morphological and structural characterization. Disintegrated cellulose fibers were then added into the HA nano dispersion and agitated for approximately an agitation time at 600 rpm at room temperature. In various embodiments, the agitation time may be approximately 15 minutes, 30 minutes, 60 minutes, 90 minutes, 120 minutes, and/or the like. Finally, the excess solution was filtered and the coated fibers were washed with a washing fluid (e.g., distilled water) multiple times (e.g., three or four times, in various embodiments) until a clear solution was obtained. The resulting fibers were oven dried at 60 °C overnight (e.g., approximately 6-10 hours). The resulting coated fibers were characterized by using SEM, EDX, FUR and TGA.

Table 1 shows the effect of the concentrations of the precursors on the concentration of the resulting HA produced. Morphology of the fiber surfaces after the treatments was obtained using SEM. Further, the extent of coating was determined using TGA.

Table 1: Different concentrations of precursors in the synthesis of HA nanoparticles

Treatment Initial concentration Initial concentration Concentration of

of Ca(OH) ₂ of H3PO4 HA produced

(mol dm ³ ) (mol dm ³ ) (mol dm ³ )

T1 1.0 0.6 0.05

T2 0.5 0.3 0.025

T3 0.25 0.15 0.0125

T4 0.125 0.075 0.00625

3.3 Preparation of HA coated cellulose fiber - cement suspension

In this experiment, cellulose fibers were coated with HA nanoparticles prior to preparation of fiber- cement composites. Concentration of the HA nano-dispersion was maintained at 0.0125, 0.025, 0.05 and 0.15 mol dm ³ during the modification process. The volumes of the precursors were adjusted to maintain the required ratios (w/w) between cellulose fibers and HA nanoparticles. As displayed in Table 2, the weight ratios between cellulose and HA nanoparticles were maintained 1 :0.25, 1 :0.5, 1 : 1 and 1 :3, respectively. Cellulose to cement ratio was kept constant at 1 : 10 throughout the experiment. For example, Table 2 describes the dry weight of components of four embodiments having cellulose to HA to cement weight ratios (CHC) of 1 :0.25: 10, 1 :0.5: 10, 1 : 1 : 10, and 1 :3: 10. Table 2: Composition of the HA coated cellulose fiber-cement suspension

Composite Dry weight (%)

Cellulose HA nanoparticles OPC

CHC 8.89 2.22 88.9

(1:0.25:10)

CHC (1:0.5:10) 8 70 4.30 87.0

CHC (1:1:10) 8 33 8.33 83.3

CHC (1:3:10) 7 14 21.43 71.4

Surface modification of the cellulose fibers was conducted according to the method described in section 3.2, except the final filtration step in various embodiments. For example, in an example embodiment, rather than performing the washing with distilled water multiple times, the HA modified cellulose pulp was further stirred for approximately 10 minutes and was allowed to settle for approximately 30 minutes, in an example embodiment. Then the required amount of cement (as given in Table 2) was added into the slurry and the total solid concentration of the slurry was maintained at ~ 20 % (w/w) by adding water. The fiber-cement slurry may then be mixed until generally homogenous and poured and/or cast. In an example embodiment, the fiber-cement slurry was mixed mechanically for approximately 10 minutes and finally the suspension was transferred into a vacuum casting box for the formation of sheets of fiber reinforced cement composite.

3.4 Formation of fiber reinforced cement sheets In an example embodiment, fiber reinforced cement sheets were prepared in laboratory scale using a vacuum dewatering technique which has been extensively used in the formation of fiber reinforced cement sheets. The suspension was transferred to an internally designed evacuable vacuum casting box (see Figures 1A and IB). The dimensions of the vacuum casting box were 150 x 100 mm ² . After dispersing the slurry homogeneously inside the vacuum casting box, ~60 KPa gauge vacuum was applied until excess water was removed.

The resulting solid cake was then transferred into a stainless steel mold (dimensions 100 x 150 mm ² ), which is shown in Figure 2B. The solid cake was pressed at 3.2 MPa pressure at room temperature using a hot press (see Figure 2A) for 15 min to remove rest of the water. After pressing, the sheets were stored at room temperature for 28 days for curing. Humidity of the storing chamber was kept constant throughout the period at 80%.

As should be understood, the fiber reinforced cement composites may be cast using a variety of methods, in various embodiments, as appropriate for the application.

3.5 Characterization of fiber reinforced cement sheets

Fiber reinforced cement composite sheets generated via an example embodiment were allowed to cure for 28 days and then subjected to characterization. All the physical and mechanical properties of the fiber reinforced cement composites such as, thickness of the composite sheets, density, moisture absorption property, water penetration property, bending strength and thermal conductivity were analyzed using the instruments available at the Sri Lanka Institute of Nanotechnology as it is and sometimes, whenever needed, the instruments were modified according to the requirement, which will be discussed hereafter. Further, the morphological studies together with the spectral imaging of the final fiber reinforced cement composites were conducted using SEMZ EDX techniques. A cross section of the fiber reinforced cement composite was attached to the sample stub using double sided carbon tape followed by a gold sputtering prior to the analysis using SEM/ EDX.

Thickness of the example fiber reinforced cement sheets were obtained using micrometer screw gauge. Average value of the thickness of ten different positions of the sheet was obtained.

An example fiber reinforced cement sheet of an example embodiment and/or generated via an example embodiment with approximately 40 mm X 60 mm was used for the test. Dry mass of the specimen was determined by drying out the test specimen in an oven at a temperature of 100 °C to 105 °C until the difference between two consecutive weighing made at an interval of not less than 2 hours was less than one percent. Volume of the specimen was determined by immersing it in water and measuring the volume of water displaced. The test specimen was saturated with water before determining the volume. The density was calculated using the equation 3.2.

p = 1000 x - (3.2)

^ v

Where,

p = the density in kg m ³

m = the mass of the test specimen after drying in g

V = the volume of the test specimen in cm ³

The above procedure was repeated for three example fiber reinforced cement sheet of an example embodiment and/or generated via an example embodiment.

Bending strength of the fiber reinforced cement sheets of an example embodiment and/or generated via an example embodiment were measured using the three point loading system as shown in Figures 3 A and 3B. The test specimen was prepared with the dimensions of 35 mm x 20 mm. Thickness of the specimen ( c ) was measured using micrometer screw gauge. As shown in Figures 3B and 3C, the tensile testing machine was modified to obtain the maximum loading at break (p).

The distance between two parallel supports was kept as 25 mm. The specimen was arranged on the supports with its smooth side up and the load was applied at mid span using the loading bar. The loading was increased at a constant speed. The bending strength was calculated using equation

3.3.

Where,

Rf = the bending strength in Mpa (N/mm ² )

P = the breaking load in N

/ = the distance between supports in mm

b = the width of the specimen in mm

c = the average thickness of the specimen

Example samples of fiber reinforced cement composite sheets of an example embodiment and/or generated via an example embodiment with 60 mm x 60 mm from each (6 replicates) of the sheets was prepared for the test. Sized specimen was immersed completely in water at a temperature of 27± 3 °C for a period of approximately 18 hrs. Surplus moisture was removed with a damp cloth and the mass of the specimen was recorded (mi). Then the specimen was placed inside a ventilated oven. The temperature was raised up to 150 °C and maintained it at that temperature for approximately 4 hrs. The dried specimen was removed and cooled for approximately 2 hours in a desiccator and weighed at room temperature. The mass was recorded (m2). The moisture absorption was calculated according to the equation given in Equation 3.4.

Moisture absorption

Where,

mi = mass in g of specimen after absorption of moisture; and

m2 = mass in g of specimen after drying

A specimen (e.g., a portion of a fiber reinforced cement composite sheets of an example embodiment and/or generated via an example embodiment) with 70 mm diameter was prepared and placed in an oven at 60 °C for 2 days and cooled in a desiccator for 2-3 hours until it reaching room temperature (e.g. , 15-25° C). Then the specimen was placed in the column as shown in Figure 4B.

The specimen sheet was made air tight using screws in the column to prevent moisture leaking from the edges. Two copper electrodes were assembled (as shown in Figure 4B) from the bottom of the column which is in contact with the outer surface of the sheet. The distance between two electrodes was kept constant at approximately 10 mm. Those two electrodes were connected to AutoFab which was programmed to measure the current passing through the two electrodes with the time by applying a constant voltage of 9 V between two electrodes. The top edge of the column was connected to inert (Nitrogen) gas stream with a constant pressure of 0.5 bar throughout the experiment. A volume of 50.0 cm ³ of water was immediately added to the column from the top and the system was closed. The setup was kept horizontally and data were collected. As the moisture penetrates gradually through the sheet, to the other end of the sheet, the AutoFab will detect a variation of the current passing between the two electrodes and the resulting increase in the current signal will be graphically displayed in the AutoFab (See Figure 5). Time required to change the current signal (t) was used to determine the extent of water penetration through the sheet. Rate of the water penetration across the sheet was calculated using the following equation (equation 3.5).

Where,

Rp - Rate of water penetration across the sheet

d _s - Thickness of the sheet

t - Time required changing the current signal

Thermal conductivity of an example prepared fiber reinforced cement composite was measured using Lee’s apparatus. Specimens (e.g., portions of fiber reinforced cement composite sheets of an example embodiment and/or generated via an example embodiment) were prepared with the dimensions of 70 mm x 70 mm. The specimen was placed in between two brass discs as shown in Figure 6. Upper brass base was heated and allowed the heat to pass through the specimen to the lower brass disc

When the apparatus is in the steady state (Temperatures Ti and T2 constant), both temperatures of brass discs were measured (Ti and T2). The Thermal Conductivity of the sheet (k) was measured according to the equation 3.6.

m ^s ( ^dT /dt) ^x (3.6)

Afa-Tz)

Where;

m - Mass of the lower disc

s - Specific Heat of the lower disc

x - Thickness of the specimen

Ti - Temperature of the lower disc at the steady state

T2 - Temperature of the upper disc at the steady state

A - Surface area of the specimen in contact with the lower disc

- Rate of cooling of the metallic disc at Ti 4 Generating A Fiber Reinforced Cement Composite

In various embodiments, the surface of delignified cellulose fibers are modified with HA nanoparticles. The surface modified (e.g., HA nanoparticles coated) delignified cellulose fibers are then mixed with cement to generate a fiber reinforced cement composite, which may cast as appropriate for the application.

4.1 Preparation of HA nanoparticles

The HA nanoparticles are formed by the co-precipitation synthesis method as described above, in various embodiments. The pH of the final suspension containing HA nanoparticles was observed as 7.8.

Powder X-ray diffraction pattern of the synthesized HA nanoparticles prepared in accordance with an example embodiment is shown in Figure 7. The PXRD pattern of the synthesized HA nanoparticles shows all the characteristic peaks in the range of 2Q, 25 - 55° for (100), (002), (210), (211), (112), (300), (202), (130), (222), (213) and (004) planes of HA confirming the formation of HA phase. Also, the relative peak intensity provides additional information to prove that the particles are in crystalline form, which will be further confirmed during the TEM analysis.

The peak intensities and d-spacing values of the PXRD pattern was compared with ICDD database and are in good agreement with the reported diffraction pattern for HA in ICDD library (PDF no. 09-0432). In addition, the absence of any additional peaks suggest that the synthesized sample contains no detectable impurities after the completion of reaction.

4.2 Morphology and structural features of the HA nanoparticles

The SEM image of HA nanoparticles obtained by wet chemical process in accordance with an example embodiment is shown in Figure 8. The electron microscopic study of the nanoparticles was conducted parallel to the modification of cellulose fibers with the same nano dispersion. The main idea was to measure the real time particle size of HA nanoparticles, remaining intact on cellulose fibers. As shown in Figure 8, HA nanoparticles show a needle-like structure with the diameter less than 50 nm with a length is about 100 - 200 nm. As evidenced in SEM micro graphs in Figure 8, the HA nanoparticle dispersion exhibits approximately homogeneous distribution of particle size.

The high resolution TEM (HRTEM) images and Fast Fourier Transform (FFT) pattern were recorded to characterize the fine structures in the morphology and crystalline structure of HA nanoparticles generated via an example embodiment. Transmission electron microscopic images in low and high resolution together with the Fast Fourier Transform (FFT) pattern and the intensity contrast profile corresponds to 211 plane as shown in Figures 9A-9D. As expected, the TEM imaging (low resolution) of the HA sample shown in Figure 9A clearly indicate that the particle diameter is less than 50 nm and also the average length of the particles vary within 100 - 200 nm. In addition, the high resolution

TEM image (HRTEM) provide further information about the crystallinity of the sample. According to it, the HA nanoparticles are in the form of poly crystalline particles. The FFT pattern of the said nanoparticles contain overlapping spot patterns, which do not form continuous rings but“spotty” rings (see the inset of Figure 9B). It is a good indication of the poly crystalline nature of HA nanoparticles.

The HRTEM intensity contrast profile recorded along the marked line in Figure 9C, corresponds to the 211 plane of HA nanoparticles which show a 2.87 nm distance for ten consecutive peaks in the intensity profile (see Figure 9D) which indicates ten adjacent atomic layers. Hence, the d- spacing of the lattice fringes corresponds to the 211 plane of HA nanoparticles which could be derived as 0.28 nm using the intensity contrast profile. These values are in good agreement with the d-spacing value obtained by the PXRD pattern of as synthesized HA nanoparticles (see Figure 7). Therefore, the data obtained by two different techniques such as PXRD and HRTEM provides same result about the synthesized HA nanoparticles of an example embodiment revealing the successful synthesis of HA nanoparticles during the surface modification of delignified cellulose fibers.

4.3 FTIR study of HA nanoparticles

Figure 10 shows the FTIR spectra of the HA nanoparticles synthesized for the modification of cellulose fibers in accordance with an example embodiment. It clearly shows (Figure 10B), the broad bands at 3432 cm ¹ and 1643 cm ¹ were attributed to absorbed water via hydrogen bonding to the OH whereas the sharp peak at 3571 cm ¹ was attributed to the stretching vibration of the lattice OH present in the HA nanoparticles.

In general the O-H stretching band is sharper and absorbs at a higher frequency when associated on to a metal than in water molecules. Therefore, the sharp peak at 3571 cm ¹ can be assigned to the stretching of non-hydrogen bonded free O-H, which are present on the surface of the crystallites of HA. Theoretically there are five vibrational modes present for phosphate ion and all are IR active and are observed in HA spectra.

The characteristic bands for PO4 ³ appeared at 565, 605, 964, 1041 and 1093 cm ¹ (Figure IOC and 10D). Two sharp peaks at 560 and 600 cm ¹ correspond to the triply degenerate bending vibrations of PO4 ³ in HA. The band appearing at 964 cm ¹ is attributed to the P-0 symmetric stretching vibration of HA while, two bands at 1041 and 1093 cm ¹ correspond to the P-0 asymmetric stretching vibrations of HA.

4.4 Thermogravimetric analysis of HA nanoparticles

As seen in the TGA results in Figure 11, weight losses in the synthesized HA nanoparticles were observed with the increase in temperature.

The TGA data concludes that the total weight loss is approximately 10 % during the temperature range of 30 - 800 °C. This weight loss arises from the removal of physically adsorbed water and decarboxylation of HA nanoparticles. A relatively prominent mass loss occurs between 30 and 100 °C, which is approximately 4.6 %, attributed to loss of physically adsorbed water molecules of the HA nanoparticles. Furthermore, the weight loss of about 5 % observed between 100 and 600 °C also attributed to the partial removal of physically and chemically adsorbed water and possibly lattice water. The weight loss above 600 °C is assumed to be the gradual dehydroxylation of HA powder.

4.5 HA nanopartides coated cellulose fibers

Various embodiments provide surface modified cellulose fibers that have been modified with HA nanoparticles. Various embodiments provide methods for generating surface modified cellulose fibers. In various embodiments, the HA nanoparticles strongly adhere to approximately the entire surface of the cellulose fibers.

The surface modification of cellulose fibers with HA nanoparticles, in accordance with an example embodiment, has been studied using SEM imaging. Figures 12B-12D shows that the entire surface of the cellulose fiber has been covered by HA nanoparticles. The disappearance of the lumens as well as the porous cavities or voids of the surface of the cellulose fibers (see Figure 12A) after the modification with HA nanoparticles (see Figures 12B-12D) is further indicative of the existence of the coating of HA nanoparticles as a top layer which is strongly bound to the surface of the cellulose fibers, as it remains intact, even after 3 to 4 cycles of washing steps.

During the swelling process, prior to the application of HA nano dispersion into the cellulose fibers, the aforementioned lumens tend to open, providing enough space for nanoparticles to enter into the voids. Due to the high surface energy of the HA nanoparticles, there is a possibility of forming hydrogen bonds with the free surface hydroxyl groups present in the structure of cellulose, which will be further discussed under the FTIR characterization of HA nanoparticles coated cellulose fibers.

Spectral imaging of HA nanoparticles coated cellulose fiber of an example embodiment, shown in Figure 13, provides additional information for the homogeneous coating of HA nanoparticles on the cellulose fiber surface. It clearly demonstrates the uniform distribution of elements such as Ca, P and O present in HA nanoparticles. Coincidence of Ca and P elemental spectra with those of C and O, further verifies that fiber surface has been completely coated with HA nanoparticles during the fiber surface modification.

4.6 EELS study of the HA nanopartides coated cellulose fibers

Electron Energy Foss Spectroscopy (EEFS) data of the HA nanoparticles coated cellulose nano composites of an example embodiment and/or generated via an example embodiment, is shown in Figure 14. The HA nanoparticle coated cellulose nano composites were washed via 3-4 washing cycles prior to the capturing of the EEFS data. The EEFS spectra show all the edges corresponds to the elements present in HA confirming the existence of HA nanoparticles on the cellulose fiber surface even after rapid washing treatments. Further, the EELS spectra of HA coated cellulose fibers show the identical edges for calcium (Ca L2, 3 at 346 eV), phosphorous (P L2, 3 at 132 eV) and oxygen (O K at 532 eV), which are the main elements of HA. The spectra also show the carbon (C) K edge at 300 eV Carbon together with oxygen could be related to the presence of cellulose fibers together with HA and also the C may be contributed from the carbon coating of the TEM grid.

4.7 PXRD analysis of HA nanoparticles coated cellulose fibers

The PXRD patterns of HA nanoparticle coated cellulose fibers (a), HA nanoparticles (b) and cellulose fibers (c), respectively, are shown in Figure 15.

It is worth to noticing that the XRD pattern of HA nanoparticle coated cellulose fibers clearly shows a broadening at around two theta of 15° and 22° which is characteristic to the cellulose peaks.

Furthermore, the line (a) of Figure 15 comprises all the characteristic peaks for HA with relatively the same intensity to those of pristine HA nanoparticles, shown by line (b) of Figure 15. PXRD study of the HA nanoparticles coated cellulose fibers of an example embodiment and/or generated via an example embodiment therefore reveals that the cellulose fibers have been successfully coated with HA nanoparticles and that coating is stable and is not being washed away even after extensive washing cycles, which is a good sign when used in fiber reinforced cement composite formation, as it involves treatments / reactions in aqueous medium.

4.8 FTIR analysis of HA nanoparticles coated cellulose fibers

The FTIR spectrum of delignified cellulose fibers is shown in Figure 16. The peaks appeared at 3400 cm ¹ and 2900 cm ¹ correspond to -OH stretching and -CH2 stretching, respectively. These absorption bands are characteristic of cellulose. The peak appearing at 1642 cm ¹ is associated with adsorbed water in cellulose and probably some hemicelluloses. The peaks at 1430, 1370, 1335 and 1320 cm 'are attributed to CH2 symmetric bending, CH bending, in-plane OH bending, CH2 rocking vibration, respectively, and the peaks at 1162, 1111, 1057, 1030 and 898 cm ¹ are assigned to asymmetric C-O-C bridge stretching, anhydroglucose ring asymmetric stretching, C-0 stretching, in-plane C-H deformation and C-H deformation of cellulose, respectively. The FUR spectra of (a) HA nanoparticles prepared via an example embodiment, (b) cellulose fibers coated with HA nanoparticles of an example embodiment and/or prepared via an example embodiment, and (c) cellulose fibers are shown in Figure 17. The band in the region from 3500- 3200 cm ¹ , assigned to cellulose hydroxyl groups was observed with decreasing relative intensity for the HA nanoparticles coated cellulose (line (b) of Figure 17) in comparison with the pure cellulose. This decrease in intensity suggests that the presence of the HA nanoparticles have affected the cellulose hydroxyl groups. Moreover, the red shift observed for the band assigned to hydrogen bonded OH (~3432 cm ¹ ) confirms strong interaction between the OH group and apatite.

Furthermore, the sharp peak observed at 3571 cm ¹ for the HA nanoparticles due to the stretching modes of non-hydrogen bonded free O-H on the surface of HA nanoparticles, had diminished in the spectrum of HA nanoparticles coated cellulose fibers (See line (b) Figure 17). That is due to the interactions of surface hydroxyl groups of HA with cellulose structures. Additionally, the shift in the P-0 stretching frequency of pure HA from 1041 cm ¹ to 1026 cm ¹ in HA nanoparticles coated cellulose fibers (Figure 18) indicates that the electron density of the PO4 ³ group is affected by the chemical interactions, mostly the hydrogen bonding between cellulose and HA nanoparticles during the surface modification. This observation is given further credence by the shift of two adjacent peaks corresponding to the PO4 ³ bending vibrations towards the lower frequencies (605 to 600 cm ¹ and 565 to 560 cm ¹ respectively) as shown in Figure 18.

It was clearly observed that the intensity of the broad peak corresponding to the absorbed water appearing around 3432 cm ¹ diminishes after the surface modification with HA nanoparticles. It suggests the unavailability of free hydroxyl groups for absorbing moisture compared to unmodified cellulose fibers, as they have been used in the formation of bonding in to the HA nanoparticles.

4.9 Example mechanism for the modification of cellulose fibers with HA nanoparticles

As a combination of all the characteristic techniques discussed here, there is enough evidence to prove the successful coating of HA nanoparticles on the cellulose fiber surface via an example embodiment. The FTIR analysis of the same composite revealed that the absorption frequencies of the phosphate groups of the HA nanoparticles have been affected during the modification and also the hydroxyl group frequencies of both cellulose fibers and HA nanoparticles of an example embodiment have also been affected. That observation can be directly correlated with the formation of inter molecular interactions between cellulose and hydroxyapatite nanoparticles (more particularly H-bonding interactions). A number of previous studies were focused on nucleation and growth of HA nanoparticles in the presence of polysaccharide and it was found that the polysaccharide’s functional groups, such as carboxyls (-COOH), sulfonic (-OSOH), amino (-NH), or hydroxyls (-OH) interact with the HA precursors by specific (ionic, electrostatic or coordinative) or non-specific (hydrogen) bonding. This is also in agreement with the bonding mechanism observed in an example embodiment, that is the cellulose’s hydroxyl groups form hydrogen bonding with the phosphate end groups present in the HA nanoparticles.

As can be seen clearly in Figure 19, -OH groups in cellulose tend to form H-bonding with the phosphate moieties where the rest of the oxygen atoms in phosphate groups have been connected to Ca ²⁺ ions to form the HA lattice. Then the remaining descent -OH groups in the cellulose ring interact with the Ca ²⁺ ions and hence, the overall bond between cellulose and HA becomes strong, which helps to keep HA nanoparticles intact with cellulose fibers.

4.10 TGA/ DTG characterization of HA nanoparticles coated cellulose fibers

TGA and DTG thermograms of delignified cellulose (a), HA nanoparticles coated cellulose fibers of an example embodiment and/or generated via an example embodiment (b) and HA nanoparticles (c) are shown in Figure 20. The inset of Figure 20 shows the DTG curves of cellulose fibers (a) and Ha coated cellulose fibers (b). Thermogram of HA nanoparticles (line (c) of Figure 20) indicates a 10% weight loss up to 800 °C. According to line (b) of Figure 20, the total weight loss of the HA nanoparticles coated cellulose fibers was about 64% due to dehydration and decomposition of cellulose component in the composite. Furthermore, it can be seen that there was no more weight losses after 650 °C, indicating that all the organic matter has been decomposed before that temperature. On the other hand, the TGA thermogram of cellulose indicates a residual weight at 800 °C which is about 5.8%. Thus, the weight percentage of the HA nanoparticles coated on cellulose is about 30.1%.

Another important aspect of the thermal analysis of the modified fiber is expressed in the inset of the Figure 20. The DTG curve of the cellulose fiber shows a maximum derivative peak at 353 °C, while the HA nanoparticles coated cellulose fibers show the same peak at 362 °C. It indicates that the HA nanoparticles coated cellulose fibers of an example embodiment are thermally more stable than the fibers without coating. This behavior may be associated with delaying heat and gas diffusion to cellulose fibers as a result of entire fiber surface being covered with HA nanoparticles.

4.11 Time optimization of the fiber modification process

Thermal analysis of the HA nanoparticle coated cellulose fibers of an example embodiment with different agitation time was conducted and the extent of coating was calculated in similar way as discussed above. The effect of the agitation time towards the extent of coating of HA nanoparticles is shown in Figure 21. In various embodiments, the agitation time is longer than 15 minutes. For example, in an example embodiment, the agitation time is at least 30 minutes. In an example embodiment, the agitation time for a homogeneous coating is 30 minutes.

4.12 Effect of the precursor concentration on the extent of coating

According to the SEM image of the HA nanoparticles coated cellulose fibers of various embodiments (Figures 22A-22D), it was observed that the initial concentration of the HA may affect the degree of coating of the cellulose fiber. As can be seen in Figure 22A, the surface of cellulose fiber has been completely covered by HA nanoparticles. The disappearance of lumens on the surface of the cellulose fibers further provides conclusive evidence for the foregoing. However, in embodiments having a lower concentration of the HA nanoparticles, the percentage of the uncoated area has increased (compared to embodiments having a higher concentration of HA nanoparticles). It can be clearly seen those uncoated areas of cellulose fibers in Figures 22C and 22D.

The TGA thermograms of cellulose fibers coated with different concentrations of HA nanoparticles provide evidence on the effect of concentration of HA nanoparticles in the reaction vessel towards the extent of coating or the filling capacity (Figure 23). It was observed that the residual weight of cellulose at 800 °C was 5.8 %. As indicated in the thermogram (Figure 23), the residual weights at 800 °C were 12.9, 20.7, 30.5 and 35.1 % for cellulose fibers coated with 0.00625, 0.0125, 0.025 and 0.05M HA nanoparticles, respectively. This confirms that the HA nanoparticles do not undergo any decomposition between 800 °C and room temperature. Therefore, it is conclusive that the remaining weight percentage of HA coated cellulose samples after 800 °C comprise of HA and the residual weight of cellulose. Hence, the percentage of HA nanoparticles loaded on cellulose fibers can be calculated as 7.1, 14. 9, 24.7 and 29.3 % by weight for cellulose fibers coated with 0.00625, 0.0125, 0.025 and 0.05 mol dm ³ HA nanoparticles, respectively.

A graphical representation of the extent of coating against the initial concentration of HA nanoparticles based on the TGA data is shown in Figure 24. While increasing the percentage loading of HA nanoparticles along with the increment of the initial HA nanoparticle concentration, it shows a tendency of reaching a saturation point around 0.05 mol dm ³ concentration of HA nanoparticles as further increase of the initial concentration does not affect the rate of the increase of the extent of coating. As indicated in Figure 24, the extent of coating was increased by only 2% when the initial concentration of HA nanoparticles increased from 0.05 mol dm ³ to 0.15 mol dm ³ . Therefore, increase of the concentration beyond 0.05 mol dm ³ of HA nanoparticles does not influence the extent of coating significantly.

The weight ratios (of dry matter) between cellulose and HA nanoparticles associated with the initial concentrations of HA nano-dispersion can be calculated as 1 :0.125, 1 :0.25, 1 :0.5 and 1 : 1 for concentrations of HA nanoparticles of 0.00625, 0.0125, 0.025 and 0.05 mol dm ³ , respectively, in various embodiments.

The FUR spectra of the cellulose fibers coated with different concentrations of HA nanoparticles are shown in Figure 25. Among the series of spectra, three important regions were found which provide evidence to show the effect of the initial concentration of HA nanoparticles towards the coating efficiency on the cellulose fibers. The intensity of the broad peaks appearing at 3432 and 1643 cm ¹ , which corresponds to the vibration frequencies of absorbed moisture, reduce gradually with the increase of the initial concentration of HA nanoparticles used for the coating. An inadequate surface coating of HA nanoparticles results in more hydroxyl groups of cellulose to be free and hence, the moisture absorption will be higher than that of fully coated fibers, which leads to increase the intensity of the peaks corresponding to the absorption of moisture.

Furthermore, the peaks appearing at 1430, 1370, 1335, 1315, 1192, 1162 and 898 cm ¹ (see the region II of Figure 26), and attributed to the vibrational frequencies of cellulose fibers as described above, tend to diminish with the increment of the concentration of HA nanoparticles. As the surface of cellulose is increasingly covered with HA nanoparticles, the penetration of IR radiation is hindered, thus the absorption of the radiation energy might be affected by the outer layer of HA nanoparticles. Therefore, this observation is in good agreement with that of the increase of the extent of coating with the increase of the concentration of HA nanoparticles. Similarly, in the region III of Figure 26, the intensities of two peaks appearing at 560 and 600 cm 1 which corresponded to the PO4 ³ bending vibrations in HA nanoparticles coated cellulose fibers, show a gradual decrease with the decrease of initial concentration of HA nanoparticles. Finally, it shows the characteristic peaks of cellulose rather than that of HA (see Figure 26-e region III).

Taken together, the data from TGA, SEM and FTIR analysis confirms that the initial concentration of the HA nanoparticles have shown a considerable impact on the loading capacity of HA nanoparticles on the cellulose fiber surface.

In summary, it was clear that the hydroxyapatite coated cellulose fibers exhibited a sound chemical interactions in between the cellulose fiber surface and hydroxyapatite nanoparticles such as H- bonding. Further the cracks and voids present on the cellulose fiber surface further supported the particles to be stacked inside the so called voids and then the entire surface of the fiber was coated and hence, the hydroxyapatite nanoparticles coated cellulose fibers were selected for the preparation of fiber reinforced cement composites.

4.13 Characterization of commercially available asbestos-cement sheet

A sample of commercially available asbestos flat sheet was characterized according to the techniques described above. All the mechanical and physical characteristic data obtained for commercial asbestos-cement sheet with standard deviations of sample means are indicated in

Table 3.

Table 3: Properties of the commercially available asbestos fiber reinforced cement sheet

Density

thickness Bending strength perpendicular to Bending strength parallel to

(mm) fiber orientation (Mpa) fiber orientation (Mpa)

(kgm ³ ) .2 ± 0.02 1672 ± 0.8 24.35 ± 0.2 18.7 ± 0.3

Water absorption Thermal conductivity

Rate of water penetration (nuns ¹ )

(% w/w) (Wm-'K ^·1 )

25.2 ± 0.1 0.55 1.5 x 10 ³

4.14 Evaluation of the properties of HA modified cellulose fiber reinforced cement sheets

Example embodiments of fiber reinforced cement sheets using cellulose fibers coated and/or loaded with HA nanoparticles were successfully produced by the laboratory scaled vacuum dewatering method (see Figure 27).

In various embodiments, the fiber reinforced cement sheets using cellulose fibers coated and/or loaded with HA nanoparticles have an initial cellulose to HA weight ratio of less than 1 :3. For example, the fiber reinforced cement sheets using cellulose fibers coated and/or loaded with HA nanoparticles have an initial cellulose to HA weight ratio of than l :x, where x is less than 3 (e.g., x = 1, and/or the like). In various embodiments x is greater than 0.1 and less than 3 (e.g., 0.1 < x

< 3) The physical and mechanical properties of HA modified cellulose fiber reinforced cement sheets measured after 28 days of curing are shown in Table 4. Composite CC (1 : 10) is a fiber reinforced cement composite formed with a weight ratio of cellulose to cement of 1 : 10, where the cellulose is not coated with HA nano particles (e.g., the cellulose fibers have not been surface modified).

Table 4: Mechanical and physical properties of HA modified cellulose fiber reinforced cement sheets Bending Water Thermal Rate of water thickness Density

Composite strength absorption conductivity penetration

(mm) (kgm ³ )

(Mpa) (% w/w) (Wm^K ¹ ) (mms ¹ )

4.96 ±

CC (1 : 10) 1434 ± 1.4 12.6 ± 0.8 30.3 ± 0.4 0.40 9.9 x 10 -2

0.04

CHC 4.91 ±

1494 ± 3.0 20.5 ± 0.5 26.0 ± 0.3 0.41 1.5 x 10 -2

(1 :0.25: 10) 0.03

CHC 4.95 ±

1504 ± 1.1 21.7 ± 0.7 26.3 ± 0.3 0.41 4.9 x 10 -3

(1 :0.5: 10) 0.08

5.04 ±

CHC (1 : 1 : 10) 1525 ± 2.8 23.1 ± 1.9 26.2 ± 0.1 0.54 2.4 x 10 -3

0.08

The bulk density of all three HA nanoparticles loaded cellulose fiber-cement composites [CHC (1 :0.25: 10) to CHC (1 : 1 : 10)] shows significant increase compared to that of unloaded cellulose fiber-cement composite (CC (1 : 10); see Figure 29). As described in the previous section, the density of these composites is mainly governed by the porosity of the composite. The incompatibility between organic and inorganic material interactions together with the inhomogeneous fiber surface with cracks and voids of the lumens promote the disjointing, which leads to a porous matrix in uncoated/untreated cellulose-cement composites.

On the other hand, the voids of the treated cellulose fibers of various embodiments are partially or completely filled with HA nano particles during the surface modification of the cellulose fibers with HA nanoparticles. Hence, the composites made with coated cellulose fibers result in less porosity compared to that of unloaded cellulose-cement composites. Thus, results in a significant increase of the density compared to uncoated cellulose fiber reinforced cement composite. Among the composites made with coated cellulose fibers, the composite CHC (1 : 1 : 10) shows the highest density, while the other two composites show gradual decrease with lower loading of HA nanoparticles (see Figure 29). Furthermore, the FTIR study of the HA nanoparticles coated cellulose fibers show that the nanoparticles tend to form hydrogen bonding with the surface hydroxyl groups of the cellulose network in addition to the physical deposition into the cracks and voids present in the fiber lumens and the surface. Thus, the HA nanoparticles exhibit a stable and strong interaction with cellulose.

The data obtained for HA nanoparticles coated cellulose fiber reinforced cement sheet (with filled voids by HA nanoparticles) shows an increase in the bending strength of about 50 - 80% as compared to the composite made from uncoated cellulose fibers with equivalent compositions between fiber and cement (CC 1 : 10) as shown in Figure 30.

Bending strength of the fiber-cement composites containing HA nanoparticles loaded cellulose fibers show a gradual increase with the increase of the coating capacity. This is attributed to the elimination of the voids associated with the cell wall of the cellulose fibers as the coating extent increases.

Physical and mechanical properties of the asbestos fiber reinforced cement sheet with asbestos to cement weight ratio of 1 :7, which was produced using the same vacuum dewatering technique under laboratory conditions as the positive control experiment are given in Table 5. The bending strength obtained for CHC (1 : 1 : 10) composite closely matched with that of the asbestos-cement composite. However, the density of the asbestos-cement composite is approximately 10% higher compared to CHC (1 : 1 : 10). This can be attributed to the low porosity and permeability in the asbestos fiber reinforced cement composites.

Table 5: Properties of the asbestos fiber reinforced cement sheet made by vacuum

dewatering method thickness Density Bending Water Thermal Rate of water

(mm) (kgm ³ ) strength absorption conductivity penetration

(Mpa) (Wm 'K ¹ ) (mins ' )

(%, w/w)

1678 ± 25.9 ±

4.98 ± 0.03 22.2 ± 0.02 0.62 5.13 x 10 ³

0.68 0.41 Both water absorption and water penetration rates are as important as the other mechanical properties such as bending strength of the fiber reinforcing cement composites. However, it is well known that the cellulose fiber reinforced cement composites are associated with performance drawbacks such as higher water absorption and higher water penetration/migration compared to asbestos cement composite materials. This is largely due to the presence of water conducting channels and voids in the cellulose fiber lumens and cell walls. The pore spaces can he filled with water during the curing of the composites as well as when it is exposed to rain. Further, the porosity of the cellulose fibers in cement composites facilitates water transport throughout the composite materials. Due to these facts, both the water absorption and water penetration rates of the cellulose fiber reinforced cement composites are significantly increased which leads to a reduction in the performance.

Figure 31 shows the percentage water absorption results for both unloaded cellulose fiber reinforced cement composite [CC (1 : 10)], and HA nanoparticle loaded cellulose fiber-cement composites such as CHC (1 :0.25: 10), CHC (1 :0.5: 10) and CHC (1 : 1 : 10), respectively. As indicated in the Figure 31, the percentage water absorption of the composites made with HA nanoparticles loaded cellulose fibers is more than about 13% low ^r er than the composites made with an equivalent formulation of unloaded fiber-cement composite. However, there is no significant change of the percentage water absorption among the HA nanoparticles loaded cellulose fiber- cement composites.

Figure 32 shows the rate of water penetration of the fiber reinforced cement sheets with and without coatings of HA nanoparticles. Composite of CHC (1 : 1 : 10) indicates the minimum rate of water penetration among all the composites. It shows 40 times lower penetration rate compared to the coated cellulose fiber reinforced cement composite. The aforementioned low rate of water penetration is mainly due to the blocking of the water transport channels in cellulose fibers as a result of the successful loading of HA nanoparticles on cellulose fibers.

Interestingly, the rate of water penetration for HA nanoparticles coated cellulose-cement composite with 1 : 1 (w/w) loading of HA nanoparticles, i.e., CHC (1 : 1 : 10) was comparatively similar to that of asbestos reinforced cement composite made under laboratory conditions. Hence, it can be concluded that the mineralization of cellulose fibers through coating of HA nanoparticles could match the rate of penetration of water through the surface of the fiber-cement composite. However, the rate of water penetration of the commercially available asbestos sheet shows a significantly lower value (see Table 5) compared to both composite sheets made under laboratory conditions. This is associated with the method of manufacturing the commercial asbestos-cement sheet, in which the possible channels of transporting water will be disturbed by the layer by layer lamination process.

Thermal conductivity of the HA nanoparticles coated and uncoated cellulose fiber reinforced cement sheets are shown in Figure 33. Composites made with uncoated cellulose fibers (CC (1 : 10)) exhibits lower thermal conductivity compared to the composites made with HA nanoparticles coated cellulose fibers. That may be associated with the higher porous structure of the cellulose fiber reinforced cement composites as they showed the lower bulk density compared to the other composites. Figure 33 clearly demonstrates the increase of the thermal conductivity of the composites with the increment of loading of HA nanoparticles during the modification of fibers. That can be correlate with the decrease of porosity due to the absence of voids and also due to the enhanced interactions between fibers and the cementitious matrix in the presence of HA nanoparticles in between the two substrates. Further addition of HA nanoparticles on the other hand increase the mineral composition of the composites, which may also lead to increase of the thermal conductivity compared to HA nanoparticles loaded cellulose-cement composites with lower loading of HA.

However, interestingly, all the fiber-cement composites made with HA nanoparticles coated cellulose fibers show lower thermal conductivity compared to that of the commercially available asbestos-cement composites. Table 6 provides a comparison of properties of asbestos cement composite sheets, untreated cellulose fiber reinforced cement composite sheets, and HA coated cellulose fiber reinforced cement sheets of an example embodiment.

Table 6: Comparison of Properties of Asbestos Cement Composite Sheets, Untreated Cellulose Fiber Reinforced Cement Composite Sheets, and HA Coated Cellulose Fiber Reinforced Cement Sheets

Commercially HA coated cellulose fiber

available Cellulose fiber reinforced cement

Properties

asbestos-cement reinforced composite sheet composite sheet cement [CHC(1 : 1 : 10)] composite sheet

[CC(1 : 10)]

Density (kg m 1434 1525

1672

³ )

Moisture 30.3 26.2

25.2

absorption (%)

Average

bending 12.6 23.1

24.3

strength

(N mm ² )

Rate of water

9.9 x 10 ² 2.4 x 10 ³

penetration 1.5 x 10 ³

(mms ¹ )

Thermal

0.4 0.54

conductivity 0.55

(W m ¹ K ¹ )

Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which the invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.