Ground tire rubber (GTR) was modified by sulfuric acid in order to improve its compatibility with and reinforcement of a polypropylene (PP) matrix. Polymer composites PP/GTR were prepared by melt mixing at different concentrations, with a maximum of 50 wt % of GTR. Studies by Fourier transform infrared spectroscopy (FTIR), surface specific area by BET (Brunauer, Emmett, and Teller), and scanning electron microscopy were used to characterize the untreated GTR and treated GTR, while the mechanical and thermal properties of the PP/GTR composites were assessed to understand how the surface treatment of GTR affected the mechanical and thermal properties of the composite PP/GTR. FTIR revealed the presence of sulfonic groups on the surface of sulfuric acid–treated GTR, and BET analyses showed an increase of about 625% in the specific surface area as a result of the high porosity produced by the treatment. In all composites containing treated GTR, a higher Young's modulus was obtained than for composites containing untreated GTR. Particularly, an increase of about 275% in the Young's modulus was obtained in composites with treated GTR (40 wt %) against that containing untreated GTR. However, a more significant reduction of the elongation at break was observed in composites containing treated GTR than in those containing untreated GTR. Also, an increase of the crystallization temperature of PP as a function of GTR was observed by differential scanning calorimetry, but the crystallinity of the composites was reduced by the addition of both untreated and treated GTR. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44858.

In this study, the graphite effect on the mechanical and fire‐retardant performance of low‐density polyethylene (LDPE) and ethylene‐vinyl‐acetate (EVA) foam composites was investigated. Polymer composites were prepared by melt mixing process and foamed by hot press molding at different graphite content (0, 3, 6, and 12 phr). Cone calorimetric tests through heat release rate (HRR) curves obtained, revealed a decreasing of 45% on peak heat release rate (pHRR) of foam composites LDPE‐EVA with 12 phr of untreated graphite content compared than those LDPE‐EVA foamed composites without graphite, which was attributed to the good distribution of graphite in the composite and more residual generates as thermogravimetric analysis suggested. Mechanical properties of polymer foamed composites with high graphite content do not show significant detrimental as a result to the formation of more uniform cells with smaller size incorporating a material with high modulus like graphite. The results suggest that polymer foam composites with graphite are suitable for the building and construction industry, in sealing and thermal insulation applications with good fire‐retardant performance.

The influence of residual wax content on the thermal, rheological, and mechanical behavior of two high‐density polyethylene (HDPE) samples from different lots of the same supplier was characterized. HDPE with a low wax content presented a higher melting temperature and a wider melting endotherm. A decrease in the degree of crystallinity and thermal stability of HDPE with a higher wax content was observed. Thermograms obtained by DSC indicated a small additional exothermic transition associated with the exclusion of residual wax. A higher wax content in HDPE produces a decrease in its viscosity due to a lubricating effect, which allows the sliding of HDPE chains of high molecular weight. In contrast, HDPE with lower wax content achieves greater elongational viscosity and melt strength. The mechanical testing results show that HDPE with higher wax content presented lower Young's modulus, tensile strength, elongation at break, and Izod impact strength than HDPE with lower wax content. The results obtained show that a relatively slight difference in wax content significantly affects HDPE properties.

This study aims to investigate the effect of ground tire rubber (GTR) treated by acetone on mechanical and morphological properties of ethylene-vinyl acetate (EVA) matrix. Polymeric EVA/GTR (0, 10, 20, 30, and 40 phr) compounds were achieved through extrusion and batch foaming process. TGA and NMR analysis revealed that oils and additives were removed from the GTR after the acetone treatment. Morphological characterization showed cell sizes below 100 μm in the compounds with treated GTR, which improved the mechanical performance of EVA/GTR compounds. The results indicated that the acetonetreated GTR are a suitable raw material to obtain foam compounds useful in vibrations absorber and isolation applications.