The role of intermolecular interactions on melt memory and thermal fractionation of semicrystalline polymers

Disappearance of Melt Memory Effect with Comonomer Incorporation in Isodimorphic Random Copolyesters

Melt memory effects in polymer crystallization have attracted much attention in the past few years. Although progress has been made in understanding how the chemical structure of polymers can affect melt memory, there are still some knowledge gaps. In this work, we study how incorporating a second comonomer unit that is partially included in the crystalline unit cell affects the melt memory effect of the major component in a random isodimorphic copolymer for the first time. This second comonomer unit depresses the melting temperature of the homopolymer, reduces the crystallinity, and distorts the crystalline unit cell. However, its effect on the stability of self-nuclei and the production of melt memory has not been studied so far. To this aim, we have selected poly[(butylene succinate)-ran-(ε-caprolactone)] random copolyesters PBS-ran-PCL that are isodimorphic, i.e., they exhibit a pseudoeutectic point. This point separates the formation of BS-rich crystals from CL-rich crystals as a function of composition. The results reveal that the melt memory effect of these isodimorphic copolymers is strongly reduced with the incorporation of even very small amounts of comonomer unit (i.e., 1 molar %). This indicates that the incorporation of a second comonomer unit in the polymer chain disrupts the intermolecular interactions present between the chain segments in the crystal lattice of the major component and reduces the capacity of the material to produce self-nuclei. This reduction is more drastic for copolymers in which the second comonomer unit is mostly rejected from the crystalline phase. Contrary to olefin-based copolymers, for copolyesters, the second comonomer unit eases the process to reach an isotropic melt state upon melting. This work reveals the impact of introducing comonomer units on the melt memory effect in isodimorphic random copolyesters.

Engineering Innovations, Challenges, and Opportunities for Lignocellulosic Biorefineries: Leveraging Biobased Polymer Production

Alternative polymer feedstocks are highly desirable to address environmental, social, and security concerns associated with petrochemical-based materials. Lignocellulosic biomass (LCB) has emerged as one critical feedstock in this regard because it is an abundant and ubiquitous renewable resource. LCB can be deconstructed to generate valuable fuels, chemicals, and small molecules/oligomers that are amenable to modification and polymerization. However, the diversity of LCB complicates the evaluation of biorefinery concepts in areas including process scale-up, production outputs, plant economics, and life-cycle management. We discuss aspects of current LCB biorefinery research with a focus on the major process stages, including feedstock selection, fractionation/deconstruction, and characterization, along with product purification, functionalization, and polymerization to manufacture valuable macromolecular materials. We highlight opportunities to valorize underutilized and complex feedstocks, leverage advanced characterization techniques to predict and manage biorefinery outputs, and increase the fraction of biomass converted into valuable products.

Ductile gas barrier poly(ester–amide)s derived from glycolide

Sustainable poly(ester–amide)s derived from glycolide have been synthesized and their thermal, mechanical, and gas barrier properties have been studied by systematically changing the number of methylene groups.