Effect of filler’s type, content and mixing method on properties of low density polyethylene/natural rubber (LDPE/NR) composites

Abstract

This study was based on preparation of low density polyethylene (LDPE) and natural rubber (NR) composites with three types of fillers (Silica, Corn Starch and Coconut Husk) and different contents (10, 20 and 30 phr) using three different mixing methods. These methods focused on the mixing order of filler into LDPE/NR (mixing I), in LDPE (mixing II) or in NR (mixing III). All the compounding is carried out by Brabender internal mixer at 150 oC for 10 minutes. In mixing I, LDPE was mixed with NR followed by addition of filler. Mixing II, LDPE was mixed with filler followed by addition of NR. Mixing III, the filler was mix with NR by two-roll mills and followed with LDPE in internal mixer. Result indicated that the tensile strength in mixing I and II methods was increased with the increasing of inorganic filler (Silica) content, but decreased with increasing content of silica in mixing III method. Silica composite in mixing II achieved the highest tensile strength. At all mixing methods the tensile strength for LDPE/NR composites with the organic fillers (Corn Starch and Coconut Husk) decreased when the filler content increased but the tensile strength with addition of corn starch in mixing II method was decreased and increased when the content of corn starch increased. The highest tensile strength for organic filler composite was obtained from the mixing I method. The highest elongation at break for LDPE/NR composite with the fillers was at LDPE/NR composite with corn starch filler but the highest tensile modulus was at LDPE/NR composite with silica filler. The tensile fracture surface of the composites and soxhlet extraction showed the morphology of NR and LDPE as well as fillers are strongly dependent on filler types and also mixing methods, where addition of silica to LDPE/NR composite was tended to prefer NR phase more than LDPE phase. Addition of corn starch filler to LDPE/NR composite designated better dispersion but with addition of coconut husk to LDPE/NR composite showed poor dispersion and morphology compared with addition of corn starch filler.