Effect of molecular weight of polylactide on chemical reactivity with joncryl chain extender

Abstract

Plastic materials are widely used in many fields today. Most of these plastics are derived from fossil fuels. However, due to increasing environmental concerns and fossil fuels being exhaustible resources, these polymers have begun to be replaced by functionally suitable alternative materials, biopolymers. Polylactide (PLA) is an aliphatic polyester that is bio-based and sustainable. It is one of the environmentally friendly polymers that can be decomposed by natural factors. This makes it a good substitute for petroleum-based polymers that are widely used in industry, for example in consumer products and packaging. Although PLA is extremely impressive in terms of use, it does have some drawbacks. Limited thermal stability, low crystallization rate and melt strength make PLA difficult to use by itself and improvements are required. Many methods are being studied to develop these properties and the most widely used of these methods is the addition of chain extenders (CE) to the material. Joncryl ADR, an oligomeric styrene-acrylic-epoxy based multifunctional chain extender, significantly improves melt properties even at low additions. The many epoxy groups it contains react with the end groups of PLA to form long chain and branched structures. Although these structures increase melt strength, they reduce the overall crystallinity of semi-crystalline PLA. In this study, three different semi-crystalline PLAs with low (L-PLA), medium (MPLA) and high (H-PLA) molecular weights were processed with two types of Joncryl chain extender, Joncryl ADR 4468 and Joncryl ADR 4400, using an internal melt mixer. Small amplitude oscillating shear (SAOS) rheology tests, differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were used for the analysis of produced samples. When the rheology analysis of Joncryl 4468 and 4400 modified samples were compared with those of neat PLA samples, a significant increase in melt viscosity was obtained as a result of chain extender addition. In addition, the melt viscosity value increased as the amount of chain extender addition increased. Joncryl 4468 has almost twice the functionality compared to 4400, resulting in a greater increase in the melt properties of PLA. When the initial molecular weight was high, branching of the structure increased the molecular weight more and showed stronger branch interactions. As a result, the material had better shape retention. The elongation rheology results showed that the melt viscosity increased with the increase of the molecular weight of PLA. Joncryl 4468 provided PLA with more branched structure and showed higher elongational viscosity during viscoelastic flow compared to 4400 modified one. DSC results showed that high Joncryl reactivity increased the crystallization temperature while decreasing the crystallinity. It was observed that as molecular weight increased, cold crystallization peaks shifted towards higher temperatures. Although no obvious change in melting temperature was obtained with increasing amount of chain extender for each PLA, a clear decrease in melting enthalpy was observed. In addition, there was no significant shift in glass transition temperatures. According to the FTIR result s, there is not a huge difference between the spectra, as all PLAs have 1.0wt% . identical bond structures and the addition percentage was at most However, Joncryl 4468 modified samples showed carbonyl peak at wavenumber 1750 cm1 as it greater increase in had more functional groups, ie more epoxy groups, compared to 4400.