Properties of PLA-co-PBSu Copolymers Rapidly Synthesized by Reactive Processing

Abstract

This work describes the synthesis of poly(lactic acid) by the ring-opening polymerization of L-lactide in the presence of oligo(butylene succinate) with two different molecular weights (Mn = 6100 and 16300 g/mol) as a macroinitiator during reactive processing. The macroinitiators were added in concentrations 1 wt%, 2.5 wt%, 5 wt%, 10 wt% and 15 wt% in respect to the L-lactide mass in the premix. The properties of the received copolymers were extensively studied with spectroscopic techniques, GPC, DSC, XRD, TGA as well as nanoindentation. Blocky copolymers were received with number average molecular weights ranging from 30 to 100 kg/mol, which decreased with increasing the PBSu content in the feed. The introduction of the flexible PBSu chains decreased the single glass transition detected, while DSC and XRD gave indications that both components crystallized in the copolymers with PBSu premix content > 5 wt%. Thermal stability was maintained and depended on the composition and molecular weight. Nanoindentation showed that despite the decreasing trend of hardness and elastic modulus with increasing PBSu content, the PLA-PBSu 2.5% copolymers had simultaneously higher elasticity modulus and strength compared to the other compositions, possibly because of a complementary effect of their high molecular weight and crystallinity. These copolymers were promising for production with continuous reactive extrusion, a novel, fast and economically viable method to commercially produce PLA-based polymers.

Segmental mobility in sustainable copolymers based on poly(lactic acid) blocks built onto poly(butylene succinate) in situ

“…That is, the PLA chains mainly crystallize and, thus, become immobile, whereas the PBSu-rich segments are mobile and their corresponding weak glass transition is enhanced at the expense of a PLA . 58,65,70 This second scenario implies a crystallization-driven phase separation, 90,91 which is compatible with recent data using X-ray diffraction, 71 denoting that the PLA chains dominate crystallization in the copolymers.…”

“…Thus, we could not conclude severe differences in semicrystalline morphology arising from the copolymer composition or from the length of the initial PBSu block. In recent findings using X-ray diffraction, 71 samples exhibited the same number of crystallization diffraction peaks in 2y positions, suggesting that PLA chains dominated in crystal formation. This result will be helpful with our discussion in the last section of this article.…”

“…Two series of diblock copolymers based on PBSu and PLA were studied (Table 1). The copolymers were synthesized employing known synthetic routes (as in previous works 72 for similar copolyesters) and these copolymers were structurally characterized in a recent work by Terzopoulou et al 71 Briefly, samples were prepared using two forms of PBSu of relatively low intrinsic viscosity [Z] (0.22 and 0.38 dL g À1 ) and low molar mass (M n , 6 and 16 kg mol À1 ), respectively. These initial forms of PBSu were referred to as ''PBSu 0.22 '' and ''PBSu 0.38 '', respectively.…”

“…Overall, five PBSu_b_PLA copolymers were prepared for each series at a PBSu/PLA ratio of 1/99, 2.5/97.5, 5/95, 10/90 and 15/85. In the initial synthesis, 71 due to the difficulty of proving the presence of only block copolymers, we could not exclude the possibility of a small amount of blend, i.e., PLA_b_PBSu_b_PLA and homo-PLA. Thus, the obtained copolymers could also be referred to as ''blocky''.…”

“…Combining PLA with polymers with faster compostability rates has been shown to be possible. 68,71,72 Comparing PLA-based systems in the form of blends or copolymers, the latter seem to be the most uniform and promising. 13,70 For the materials studied in the present work, lowering of the T g and melting point and improvement of physical enzymatic hydrolysis in soil were paramount.…”