Abstract. Devulcanization of ground tire rubber (GTR) was done using twin screw extruder (TSE) and internal mixer (IM). Processing parameters were varied to analyze its effect on gel content. Fourier Transform Infrared Spectroscopy (FTIR) analysis was performed as qualitative technique to confirm structural change. The devulcanized rubbers with the least gel content percentage produced in both TSE and IM were then used as filler in natural rubber (NR)/coconut coir (CC) composite preparation. Effects of gel content percentage on NR/CC composite tensile strength and elongation at break were analyzed. The results show that the gel content decreased by 41% for sample processed in TSE and 50% in IM compared to control sample. Overall, the devulcanization is influenced by high energy generated by thermal or thermo-mechanical process. FTIR spectra show chemically structural changes of GTR as C=C, CH2, CH3with higher intensity for IM sample than its counterpart indicated devulcanization. The replacement of GTR to DGTR on NR/CC/GTR composites provided less network structures and resulted better tensile strength and elongation at break.
The in-flow and cross-flow shrinkage of injected molding polyamide 66 (PA66) could be effectively reduced by optimizing glass fiber content and molding condition. The chosen molding conditions were melt temperature, cooling time and cooling temperature. The filler effect between glass fiber and clay on PA66 shrinkage also being compared. The result showed that glass fiber can effectively reduce the in-flow and cross-flow shrinkage by giving 54% to 86% reduction of shrinkage percentage. The optimum shrinkage was predicted sequentially at glass fiber content, melting temperature, cooling time and cooling temperature for in-flow are 45%; 285 °C; 45 seconds; 90 °C and for cross-flow are 45%; 285 °C; 35 seconds; 60 °C. The verification for cross-flow shrinkage was 0.41%, while the predicted value was 0.39%. The optimum cross-flow molding condition was applied to PA66/clay composite giving 28% to 51% reduction for 1% to 5% clay and 23% to 77% reduction for 15 % to 45 % clay. The shrinkage reduction by clay was lower than glass fiber, however, the addition of clay giving isotropic shrinkage that leads to less warpage.
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