Synthesis and properties of poly(lactic acid) glycolysates-crosslinked epoxidized natural rubber

Abstract

This research is aimed to developed cured rubber materials by using a novel crosslinker, polylactic acid glycolysates (GPLA). Effects of chain lengths and contents of GPLA on chemical structures and the degree of crosslinking of epoxidized natural rubber (ENR) by employing chemical reactions and reactive cross linking processes are investigated. NMR, MALDI-TOF, and FTIR spectra indicate 3 possible chemical structures of GPLA-cured ENR, which are “crosslinked”, “grafted” and “simple blend” structures. In a chemical reaction method, mechanism of crosslinking is dependent on sizes of the crosslinker. In an early stage, the crosslinker disperses into ENR matrix with a progress of crosslinking reaction. After the reaction, large-sized crosslinker molecules (G44) are separated from ENR, and 2-phase morphology is observed. In contrast crosslinkers (G10 and G2) act as stabilizer after crosslinking reaction. Crosslinking efficiency of the samples from the reactive crosslinking method is examined by MDR. An optimum ENR: crosslinker ratio of 2:1 is observed. G44 cured ENR with a 33wt% content shows the highest tensile tensile strength, likely due to its high content of the “crosslinked: structure and partly due to high modulus of the polymer chains. The incorporation of G10 leads to an improvement in tensile modulus, due to the higher degree of chain entanglements derived from the high contents of “grafted’ structure. The resulting GPLA-cured ENR materials with different chemical structures are further applied as toughening agents for polylactic acid (PLA) products. An incorporation of GPA- cured ENR, at 5 wt%, into a commercial PLA resin shows an improvement in elongation at break, without significant decrease in tensile strength and modulus of the PLA matrix A further increase of the contents to 10-15 wt%. however, results in a slight drop in these properties. At this high blend compositions range, G44- and G10-cured ENR are more effective in improving tensile and impact strengths of PLA resin, compared to the small- sized ENR.