Natinee Lopattananon

Effect of Nanoclay Addition on Morphology and Elastomeric Properties of Dynamically Vulcanized Natural Rubber/Polypropylene Nanocomposites

Abstract Thermoplastic vulcanizate (TPV) nanocomposites based on 60/40 (%wt) natural rubber (NR)/polypropylene (PP) blends were prepared by melt blending in an internal mixer. Sodium montmorillonite (Na-MMT) was first added in natural rubber latex to obtain natural rubber/clay masterbatch, which was subsequently dynamically crosslinked while mixing with molten PP. The effect of Na-MMT content were examined concerning elastomeric properties of NR/PP blends dynamically vulcanized using phenolic resin as a curing agent. Morphology characterization observed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and 3D microfocus X-ray computerized tomography showed that the dynamic vulcanization with nanoclay addition changed the blend morphology from a co-continuous-like structure to droplet-like phase one, and the clay remained within NR phase in intercalated and aggregated forms. Furthermore, the presence of clay induced the decrease in crosslinking of NR, but promoted the mixing between NR and PP during dynamic vulcanization. This suggested that nanoclay worked as a kind of morphology modifier during dynamic vulcanization. The addition of clay marginally enhanced the 100 % modulus and tensile strength, but led to the decrease of the elongation at break. The optimal level of tensile strength improvement was obtained with loading of 5 phr clay. The permanent set of the NR/PP/Clay TPV nanocomposites was well maintained at the acceptable level as elastomer. The resistances to oil and heat were improved with incorporation of clay, proportional to clay loading. The experimental results indicated that the nanoclay had a positive effect on improving the 60/40 NR/PP blend morphology, which provided a little benefit to strength of the TPVs. However, the addition of nanoclay offered an improvement in oil and thermal resistances due to a combined effect of the clay dispersion and improved morphology of NR and PP blends.

Sustainable Biocomposites from Rice Flour and Sisal Fiber: Effect of Fiber Loading, Length and Alkali Treatment

Abstract Rice flour was modified with water and glycerol in single-screw extruder to obtain bioplastic of low manufacturing cost. Sisal fibers were used as reinforcing fillers to enhance rice flour-based bioplastic properties. The effects of short sisal fiber content (5 to 20 wt.%), length (0.2 to 6 mm) and alkali treatment (5% w/v NaOH) on the moisture content, tensile properties, impact properties, dynamic mechanical properties and morphology of the biocomposites were studied. The results showed that incorporation of the sisal fibers with a fixed fiber length into the bioplastics improved moisture resistance, tensile strength, impact strength and storage modulus, and that the improvement level increased with increasing sisal fiber content. The optimum reinforcement was achieved at 20 wt.% of fiber loading and 4 mm long fibers. The tensile strength of the biocomposite was about 4 times more than that of the neat rice flour-based bioplastic. The use of 5% NaOH aqueous solution further improved the moisture resistance and mechanical properties of the biocomposites, mainly resulting from better interfacial adhesion between the sisal fiber and rice flour matrix. Furthermore, the performance of the rice flour-based bioplastics synergistically combined with the sisal fibers suggests that they have great potential in development of environmentally friendly/sustainable biomaterial products from renewable resources.

Compatibilization of silica-filled natural rubber compounds by combined effects of functionalized low molecular weight rubber and silane

Epoxidized low molecular weight natural rubber (ELMWNR) with 28 mol% epoxide groups and weight average molecular weight of 49,000 g mol−1 was prepared by oxidative degradation of epoxidized natural rubber (NR) using periodic acid in the latex state. ELMWNR-28 was used at 10 parts per hundred parts of rubber (phr) loading in combination with bis-(triethoxysilylpropyl) tetrasulfide (TESPT) as the silane coupling agent in the range of 0–4.5 phr in silica-reinforced NR compounds. The use of TESPT in combination with ELMWNR-28 gives lower mixing torques and compound viscosities compared with the use of TESPT alone and the system without any compatibilizer. The bound rubber content, modulus, and tensile strength of the compounds with only TESPT strongly depend on the TESPT loading. The use of ELMWNR-28 as a compatibilizer clearly improves such properties compared with the non-compatibilized systems. By adding TESPT into the compound with ELMWNR-28, the properties further improve with increasing TESPT loading. The combined effect of ELMWNR-28 at 10 phr with a small amount of TESPT at 1.5 phr results in compounds with superior processability (i.e. low Mooney viscosity and Payne effect), and only slightly lower modulus and reinforcement index (M300/M100) compared with the use of the optimum content of TESPT. This compatibilizer/TESPT combination has the environmental benefits that the ELMWNR is a naturally based product, and that the reduced amount of TESPT silane coupling agent emits a greatly reduced amount of ethanol during processing.

Surface Modification of TiO2 Nanoparticles by Grafting with Silane Coupling Agent

Titanium dioxide (TiO2) possesses excellent photocatalytic activity and provides UV protection for polymeric materials. The nanosized TiO2 particles with larger surface area to volume ratio and an increased surface reactivity shall impart better photocatalysis and UV protection efficiency to the rubber compounds, compared to the use of conventional micron-sized particles. Direct incorporation of TiO2 nanoparticles (n-TiO2) into non-polar rubbers faces incompatibility problem between the two phases. One of the solutions to overcome this problem is to treat the nanoparticle surface by using silane coupling agent such as bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT). This work prepared n-TiO2 from commercial micron sized-TiO2 by ultrasonication technique. Particle size of TiO2 was measured by laser light scattering particle size analyzer. The morphology of TiO2 nanoparticles was characterized by field emission scanning electron microscope (FESEM). The grafting reaction of silane on TiO2 nanoparticles surface was studied at varying reaction temperatures and times. The purified grafted materials were characterized by energy dispersive X-ray analysis (EDX), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The characterization data confirm a presence of grafted silane on the TiO2 nanoparticles surface. The result shows that ultrasonication technique can effectively decrease particle size and the grafting reaction of silane coupling agent onto TiO2 nanoparticles can be successfully carried out at 140°C for 8 h.

Polymeric Antioxidant Based on Natural Rubber Grafted with N-(4-Hydroxyphenyl)maleimide

A novel rubber bound antioxidant NR-g-HPM was prepared by melt grafting HPM (N-(4-hydroxyphenyl)maleimide) onto natural rubber in a brabender plasticorder. HPM was synthesized from p-aminophenol and maleic anhydride. The yield was found to be over 80%. The grafting products were observed with FTIR spectroscopy and TGA. The ageing resistance of natural rubber vulcanizates using NR-g-HPM was studied. It was found that an optimal amount of NR-g-HPM (6 phr) gave about 25% better tensile strength and elongation at break as compared with conventional BHT addition, for filled natural rubber after 48 h of accelerated aging.

Surface Modification of Silica Nanoparticles for Reinforcement of Epoxidized Natural Rubber

Epoxidized natural rubber (ENR) based nanocomposites were prepared by mixing ENR latex (epoxide content of 35 mole%) with silica nanoparticles (SiO2). SiO2 were previously treated with 3-aminopropyltriethoxysilane (APS) and 3-methacryloxypropyltrimethoxysilane (MPS). Morphological and mechanical properties of ENR/SiO2 composites were investigated. The dispersion of SiO2 in ENR matrix, which was characterized by SEM, indicated that the treated SiO2 exhibited better dispersion than that of the untreated SiO2. Moreover, it has been found that the modified SiO2 with either APS or MPS gave much significant reinforcing effect than the untreated one. However, the treatment of SiO2 nanoparticles with MPS resulted in better interfacial interaction when the APS treatment was compared.

Properties of Thermoplastic Natural Rubber (TPNR): Influence of Polypropylene Grades on TPNR Properties

Thermoplastic vulcanizate (TPV) based on natural rubber (NR) and polypropylene (PP) blends were successfully prepared through a dynamic vulcanization process using Brabender Plastograph EC Plus with a rotor speed of 60 rpm at 180°C. Sulfur vulcanization system was used to cure rubber phase in the TPVs. Three grades of PP (i.e., PP700J, HP553R and HP544T) were used to blend with NR at a fixed blend ratio of NR/PP = 60/40. The mechanical properties, crosslink density, complex viscosity and morphological properties of the blends were examined. The results revealed that the dynamically cured NR/PP700J samples showed the best mechanical properties because of higher crosslink density and smaller rubber particle size when compared with those of the blends combined with HP553R and HP544T. Furthermore, the complex viscosity of the TPVs was highest for the blends with PP700J.

Property enhancement of silica-filled natural rubber compatibilized with epoxidized low molecular weight rubber by extra sulfur

The properties of both compounds and vulcanizates of silica-filled natural rubber (NR) compatibilized with epoxidized low molecular weight natural rubbers (ELMWNRs) consisting of 12 and 28 mol% epoxide are investigated. The ELMWNRs with a molecular weight range of 50,000 to 60,000 g/mol are produced by depolymerization of epoxidized natural rubber (ENR) latex using periodic acid, and then used as compatibilizer in a range of 0 to 15 phr in virgin NR. The compounds with LMWNR without epoxide groups, and with bis-(triethoxysilylpropyl) tetrasulfide (TESPT) coupling agent are also prepared for comparison purpose. Incorporation of ELMWNRs lowers Mooney viscosity and Payne effect to the level closed to that of silica/TESPT compound, and clearly enhances the modulus and tensile strength of vulcanizates compared to the compounds with no compatibilizer and LMWNR. The higher epoxide groups content results in the better tensile properties but somewhat less than the compound with TESPT. Addition of extra sulfur into the compounds with LMWNR and ELMWNRs to compensate for the sulfur released from silane molecule in the silica/TESPT system shows small influence on Mooney viscosity, but remarkably enhances 300% modulus, tensile strength and loss tangent at 60°C as a result of the better network formation.

Comparative Study of NR/BR/PP and NR/NBR/PP Ternary Blends for High Abrasion Resistant Thermoplastic Vulcanizates

High abrasion thermoplastic vulcanizates (TPVs) based on natural rubber (NR)/butadiene rubber (BR)/polypropylene (PP) and NR/acrylonitrile butadiene rubber (NBR)/PP were prepared using melt blending method. The rubber blends of 40/60 NR/BR and 40/60 NR/NBR were firstly prepared to investigate their mechanical and wear-resistant properties. The results indicated that the abrasion resistance of NR/BR blend was much higher than that of the NR/NBR blend, but the tensile strength and elongation at break were lower. TPVs made of NR/BR/PP and NR/NBR/PP blends were then prepared by melt-mixing the rubber blends (i.e., NR/BR or NR/NBR) and PP with composition of rubber to plastic of 60/40. It was found that the NR/BR/PP TPV showed higher strength and abrasion resistance when compared with the NR/NBR/PP TPV due to smaller domain of vulcanized rubber particles. The present study also suggested that the abrasion resistance of NR/BR/PP TPV was slightly lower than that of nylon 6.

Bioplastics from Blends of Cassava and Rice Flours: The Effect of Blend Composition

Abstract Bioplastics from melt-mixing of cassava flour, rice flour and their blends with compositions of between 0/100 and 100/0 %wt were successfully obtained using twin-screw extrusion and compression molding processes. The influence of blend composition on the bioplastics properties was studied. It was found that the flour blends were uniformly mixed. The tensile properties and dynamic properties of the flour bioplastics were examined. The tensile strength and storage modulus of compression molded bioplastics based on rice flour was greater than those of the cassava flour, but their flexibility was lower. The tensile strength and storage modulus of the flour blend bioplastics increased with increasing rice flour content. The flour bioplastics showed two glass transitions, one corresponding to glycerol rich phase and the other corresponding to plasticized starch. For plasticized flour blends, the glass transitions were not affected by the blend composition. The improvement in the mechanical properties of the bioplastics produced from the cassava/rice flour blend could be explained by an increase in the crystallinity level resulting from the higher concentration of rice flour. Using flour blends derived from cassava and rice flours, the bioplastics developed in this study offer a greater performance while maintaining environmental compatibility and sustainability, which allows for a substitution of tradition bioplastics from cassava starch.