Improving Processing, Crystallization, and Performance of Poly-l-lactide with an Amide-Based Organic Compound as Both Plasticizer and Nucleating Agent

Abstract

In this work, we report on a novel hydrogenb o n d i n g c o m p o u n d , N , N ′ -b i s ( 2 -h y d r ox y e t h y l )terephthalamide (BHET), and its potential as additive in poly-L-lactide (PLA). Although the hydroxyl groups of BHET can participate in transesterification with the PLA matrix, we demonstrate through gel permeation chromatography that extrusion at 200 °C does not result in a drastic decrease in molecular weight. When dissolved in the PLA matrix, BHET facilitates a plasticizing effect, indicated by a suppression in both melt viscosity and glass-transition temperature. Additionally, BHET can crystallize from the PLA melt during cooling, where the generated BHET crystals facilitate heterogeneous nucleation of the PLA matrix. In general, BHET crystallization is favored at high undercooling/superstaturation, as this yields BHET crystals with a high surface area-to-volume ratio. However, rapid cooling to temperatures below the glass-transition temperature prevents the crystallization of the BHET, effectively yielding samples where only the plasticizing effect of BHET is evident. A suppression in yield point is observed during mechanical analysis of samples with increasing BHET concentration, a characteristic feature for samples with decreasing glass-transition temperatures. In contrast, when allowed to crystallize during processing, BHET can be used to generate PLA crystals oriented along the flow direction, effectively enhancing the tensile modulus. Overall, the combined plasticizing and nucleating effect of BHET makes it a verstaile additive for controlled processing and performance of PLA.

Nucleating Agents to Enhance Poly(l-Lactide) Fiber Crystallization during Industrial-Scale Melt Spinning

“…The molecular weight of the processed PLA samples containing talc remained the same as the processed samples of pure PLA, indicating that talc does not trigger PLA degradation during processing. The molecular weight of the samples containing 2% ( w / w ) BHET was slightly lower than that of the other processed samples, in agreement with a previous study using this additive [ 35 ]. However, this effect was more prominent in our process, reflecting a longer exposure of the samples to high temperature and shear stress in our industrial-scale device compared to the laboratory equipment used for the earlier study.…”

“…We used PLA grade Luminy L130 (Total-Corbion, Gorinchem, Netherlands), which is composed of <99% stereochemically pure poly( l -lactide) with a T g of 55–60 °C and a melting point (T m ) of ~175 °C. The nucleating agent BHET ( Figure 1 ), with a T m of 350 °C, was synthesized as previously described [ 35 ]. The melting behavior of BHET is unstable because it degrades directly after melting and must be dried before use.…”

“…BHET acts as a plasticizer in the melt before self-organizing into needle-like structures above the crystallization temperature (T c ) of PLA. BHET has a high affinity for PLA and is therefore completely miscible in the PLA matrix, providing a large surface area for heterogeneous nucleation during bulk processing [ 35 ]. BHET has not yet been tested for high-velocity melt spinning, but we predicted that the replacement of talc with BHET would increase the X c by altering the crystalline structure and therewith the crystallization behavior [ 36 ].…”

Supramolecular Interactions in Hybrid Polylactide Blends—The Structures, Mechanisms and Properties

“…N , N ′-Bis(2-hydroxyethyl)-terephthalamide (BHET, Scheme 1 ) can be a versatile additive for PLLA, operating both as a plasticizer for processing purposes and as a nucleating agent [ 41 ]. BHET crystallizes from the PLA melt during cooling, and the formed crystals facilitate heterogeneous nucleation in the PLA matrix.…”

Thermal Performances and Fluidity of Biodegradable Poly(L-lactic acid) Filled with N, N'-Oxalyl Bis(piperonylic acid) Dihydrazide as a Nucleating Agent

“…[15,16]. A large number of compounds with different structures, like talc [17], calcium carbonate [18], zinc citrate [19], benzoylhydrazine derivatives [12,20], amide derivatives [21,22], etc., were employed to investigate their role in crystallization process of PLLA. Even so, it is still difficult to reveal the relationship between structure and nucleation effect for PLLA, whereas thoroughly revealing this relationship is very valuable to develop the efficient and commercial nucleating agents for PLLA.…”