Sawdust powder filled natural rubber composites were prepared by incorporation of different loadings (20100 phr) of sawdust powder fillers. Two series of composites were studied, i.e. composites with and without maleic anhydride grafted natural rubber (NRgMAH). Grafting of maleic anhydride onto the natural rubber was done prior to compounding using an internal mixer at 145°C. The curing characteristics, hardness property and tensile properties of the composites were studied. Results indicate that the scorch time and cure time decrease with increasing filler loading whereas the maximum torque exhibit an increasing trend. Increasing sawdust powder content also increases the tensile modulus and shows superior hardness property over than 80 shore A, but the tensile strength and elongation at break decrease. As the filler loading increases, the rubberfiller interactions of the composites decrease. The interfacial interaction of sawdust powder filler and natural rubber matrix was enhanced by the addition of NRgMAH, as exhibited by the fracture surfaces of the composites using a Scanning Electron Microscope (SEM) and rubberfiller interaction studies. The presence of NRgMAH has prolonged the curing time and scorch time and enhanced the tensile properties.

Reclaimed rubber (RR) from waste tires was introduced as a wood adhesive by blending with epoxidized natural rubber (ENR). To improve the polarity of RR and compatibility with ENR, maleic anhydride (MA) was grafted onto RR chains. Influences of RR and RR-g-MA (maleic anhydride grafted reclaimed rubber) on the adhesion of wood adhesive along with their properties such as crosslinking, mechanical properties, thermal stability, and wettability were studied. It was found that RR and RR-g-MA affect the vulcanization of ENR by increasing crosslink density. Especially, in the case of using RR-g-MA generates a new form of an ester linkage. The higher crosslink density together with the formation of ester linkages results in superior thermal stability by the addition of RR-g-MA. In addition, the incorporation of RR exhibited an increase in the lap shear strength when compared with the pure ENR. This improvement is due to the increased crosslink density because the presence of RR resulted in the enhanced cohesive strength of rubber adhesive. Additionally, the incorporation of RR-g-MA showed higher efficiency to improve the adhesion of rubber adhesive. The addition of RR-g-MA has not only enhanced the cohesive strength of rubber adhesive, but also increased the adhesive strength from the interaction between the hydroxy group in cellulose on the wood surface and the polar functional group (i.e., oxirane rings of ENR, maleic group of RR-g-MA and ester group of ester linkage) of rubber adhesive. Therefore, the cohesive fracture was observed in ENR/RR-g-MA adhesive. HIGHLIGHTS The worn-out rubber tire as a mass waste can be utilized to develop effective adhesives The addition of maleic anhydride grafted reclaimed rubber caused to generate new ester linkage between epoxidized natural rubber chains The epoxidized natural rubber vulcanizates with maleic anhydride grafted reclaimed rubber showed superior thermal stability The addition of maleic anhydride grafted reclaimed rubber enhanced the adhesive strength of rubber adhesive from the interaction between hydroxy group in cellulose on the wood surface and the polar functional group of rubber adhesive GRAPHICAL ABSTRACT

The preparation and mechanical properties of natural rubber latex foam (NRLF) using calcium carbonate (CaCO3) or combinations of CaCO3 and crumb rubber (CRM) as fillers were investigated. The CaCO3 contents were varied as 10, 20, and 30 phr. The ratios of CaCO3/CRM at 0.5/1.0, 0.75/0.75 and 1.0/0.5 were used. The experimental findings were that CaCO3 was well dispersed and blended with the natural rubber latex. The density of the NRLF increased with the increase in CaCO3 content. The foam containing less than 20 phr of CaCO3 showed higher tensile strength and elongation at the break than natural rubber latex foam without CaCO3. The percentage of compression set and depression of NRLF increased with increasing CaCO3 content. When the mixture of CaCO3 and CRM was used as a filler in NRLF, it was found that both CaCO3 and CRM were well dispersed and mixed with natural rubber latex. The NRLF containing the mixture of CaCO3 and CRM was more flexible than the foam containing only CaCO3. Furthermore, the NRLF with CaCO3 and CRM at the ratio of0.75/0.75 showed more uniform bubble shape and higher density than foam with other CaCO3/CRM ratios. The tensile strength of the foam decreased with decreasing CRM content, while the percentage of depression was low when the proportion of the CRM was reduced. Furthermore, the foam containing CaCO3/CRM ratio of 0.75/0.75 showed the lowest compression set.

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