Ekrachan Chaichana

Polyethylene/clay nanocomposites produced by in situ polymerization with zirconocene/MAO catalyst

Two commercial nanoclays were used here as catalytic fillers for production of polyethylene (PE) and linear low-density polyethylene (LLDPE) nanocomposites via in situ polymerization with zirconocene/MAO catalyst. It was found that both types of nanoclays designated as clay A and clay B can improve thermal stability to the host polymers as observed froma thermal gravimetric analysis (TGA). The distribution of the clays inside the polymer matrices appeared good due to the in situ polymerization system into which the clays were introduced during the polymer forming reaction. Upon investigating the clays by X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR), it was observed that the crucial differences between the two clays are the crystallite sizes (A < B) and the amounts of amine group (A < B). The higher amount of amine group in clay B was supposed to be a major reason for the lower catalytic activity of the polymerization systems compared to clay A resulting from its deactivating effect on zirconocene catalyst. However, for both clays, increasing their contents in the polymerization systems reduced the catalytic activity due to the higher steric hindrance occurring.

Synthesis of polyethylene/coir dust hybrid filler via in situ polymerization with zirconocene/MAO catalyst for use in natural rubber biocomposites

In This study, polyethylene/coir dust hybrid filler was synthesized by in situ polymerization using a zirconocene/MAO catalytic system. The obtained hybrid filler was then used for the production of natural rubber biocomposites. The synthesis process of the filler was investigated with variation of coir dust loadings. It was found that increasing the amount of coir dust decreased the catalytic activities due to negative supporting effects. After introducing the PE/coir dust hybrid filler into natural rubber, SEM micrographs showed that the PE/coir dust filler were more compatible with the natural rubber matrix than the pure coir dust. This is owing to the hydrophobicity of the polyethylene in the hybrid filler. The results from a dynamic mechanical analysis showed that the natural rubber biocomposites with the hybrid filler provided a greater storage modulus than that with the pure coir dust. This suggests that the enhanced stiffness of the natural rubber biocomposites is probably due to the strong interaction between the hybrid filler and the natural rubber matrix. The strong interaction in the biocomposite can be confirmed by the low value of a loss factor (tan δ), which indicates a low degree of molecular mobility of the polymer chains, resulted from good adhesion on the filler surfaces.

Enhancing Properties of Deproteinized Natural Rubber with Rice Husk Ash Silica for Use as a Dental Material

Rice husk is an agricultural residue from a rice-mill known as a rich source of silica. In this study, the rice husk was extracted for the contained silica by pretreatment with hydrochloric and calcination at 700 °C, and the white rice husk ash (WRA) mainly consisting of the silica was finally obtained. WRA was then investigated for its composition and structure with X-ray fluorescence (XRF) and X-ray diffractometer (XRD). The results showed that WRA contained a large amount of silica (90%) with amorphous structure. After that, WRA was used as filler for the preparation of natural rubber products. Two kinds of the natural rubber products were prepared here: 1) the pure natural rubber (PNR) product and 2) the deproteinized natural rubber (DNR) product. DNR was a protein removal natural rubber which is suitable for use as a dental material with the low allergenic properties caused from the proteins. Additionally, DNR used in this study could be provided by removing proteins from the natural rubber latex with 0.1 % urea in the presence of surfactant at room temperature. It was found that the nitrogen content (main element of proteins) of DNR was lower than PNR under the test condition. For the preparation of natural rubber products, WRA was mixed into the PNR and DNR latexes comparing with the commercial silica (Hisil-233). All finished latexes were compounded to obtain the natural rubber products. The viscoelastic properties and the cure characteristics of the entire products were investigated. It can be observed that WRA can be comparable with the commercial silica for use as filler for the natural rubber products. This is an attractive option to produce dental materials from the agricultural residues, which will reduce the cost of the production and also add value to the agricultural residues.

Study on Mechanical Properties of Natural Rubber Filled with Molasses Black/Carbon Black Hybrid Filler System

Molasses is an inexpensive byproduct made during the extraction of sugars from sugarcane. Viscous molasses was converted to powder form under heating process. Molasses black (MB), mainly consisting of carbon, was finally obtained. As a result of elemental analyzer, it is evident that MB containing 56.13 % of carbon. Additionally, Fourier Transform Infrared Spectrophotometer (FTIR) result confirmed that function groups of MB were comparable with carbon black (CB). Nevertheless, the large particle size and low specific surface area of MB was less effective for reinforcement. Therefore, in this research, a feasibility study was carried out on the utilization of MB together with carbon black as hybrid filler in natural rubber (NR). Reinforcement of NR with MB/CB hybrid filler at various ratios was studied. The total hybrid filler content was 30 parts per hundred of rubber (phr). The mechanical properties were determined. The results revealed that the NR vulcanizates containing hybrid filler exhibited the better reinforcement than that filled with single MB filler.

Use of Coir-Filled LLDPE as a Reinforcement for Natural Rubber Composite

Cellulose based fibers such as sisal, jute and coir are ones of the most frequently used reinforcing fillers for composite materials including natural rubber composites because they can improve mechanical properties of their composites. However, the main disadvantages of these composites are the poor compatibility between the fiber surface and the host matrices, mainly due to the highly hydrophilic character of the fibers and the hydrophobic character of the host materials. Therefore, in this research, coir had been modified with linear low-density polyethylene (LLDPE) prior to introducing into the natural rubber composites. The coir-filled LLDPE was synthesized by in situ polymerization with MAO/metallocene catalyst, named as modified coir. The unmodified coir and modified coir were then blended with natural rubber latex to obtain natural rubber composites. The morphology and thermal dynamic mechanical properties of the composites were investigated by scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA). The composites blended with the modified coir showed the better compatibility between the coir and the natural rubber than those with the unmodified coir. In addition, they also showed the greater storage modulus and lower tan delta than the unmodified counterpart and the pure natural rubber without the reinforcement.