Toward Heat-Resistant and Transparent Poly(l-lactide) by Tailoring Crystallization with an Aliphatic Amide as a Nucleating Agent

Abstract

Poly(L-lactide) (PLLA) has been known as an important bioplastic with tremendous potential to replace some conventional fossil-based plastics; however, its commercial application still faces great challenges in terms of the implacable contradiction between high thermomechanical properties and exceptional optical transparency. Herein, we report a feasible and promising strategy to address this challenge by utilizing N,Nethylenebis(12-hydroxystearamide) (EBH) as an efficient nucleating agent (NA) to tailor the crystallization of PLLA. The results show that the presence of EBH can not only accelerate the melt crystallization of PLLA but also remarkably decrease the size of the crystals formed in the crystallization at low temperatures of 80−90 °C. Further analysis indicates that the EBH molecules dispersed in PLLA melt could self-organize into nanofibrous network structures upon cooling, which can provide an extremely large nucleation surface for the growth of numerous nanosized crystals. Consequently, highly crystallized (the crystallinity is as high as 45%) PLLA sheets with an impressive combination of superb heat resistance and good transparency (the clarity is ca. 70%) have been successfully fabricated by melt processing with the aid of 0.4−0.8 wt % EBH. Our work offers a new opportunity to develop heat-resistant and transparent PLLA materials.

Integration of Stiffness, Ductility, Heat Resistance, and Transparency for Polylactide Films by Manipulation of Amorphous Chain Networks and Oriented Nanocrystals

“…According to the Rayleigh theory, when the crystal size decreases to the nanometer level (i.e., much less than the wavelength of visible light, about 400–780 nm), the light scattering effect will become very weak, thereby ensuring high transmittance . For instance, Bai et al have tailored the crystallization process of PLA by adding a nucleating agent EBH, which can self-assemble to nanofibrous network structures, provide a large nucleation surface for crystal growth upon processing, and obtain good transparency . Wu et al have reported ternary PLA/poly­(methyl methacrylate) (PMMA)/α-cellulose blends with high light transmittance.…”

“…57 For instance, Bai et al have tailored the crystallization process of PLA by adding a nucleating agent EBH, which can self-assemble to nanofibrous network structures, provide a large nucleation surface for crystal growth upon processing, and obtain good transparency. 58 Wu et al have reported ternary PLA/poly(methyl methacrylate) (PMMA)/α-cellulose blends with high light transmittance. They believe that this is attributable to the introduction of αcellulose, which provides more crystallization sites and imparts smaller crystallites to PLA.…”

Assessment of Polylactide as Optical Material

“…Promising results are achieved by the application of N,N'-ethylenebis(stearamide) (EBS) or N,N'-ethylenebis(12-hydroxystearamide) (EBHS) as nucleating agents 41,[195][196][197][198] . While both promote crystallization, an increase in the annealed samples' transparency and haze <10 % is reported 41,[195][196][197][198] .…”

“…Promising results are achieved by the application of N,N'-ethylenebis(stearamide) (EBS) or N,N'-ethylenebis(12-hydroxystearamide) (EBHS) as nucleating agents 41,[195][196][197][198] . While both promote crystallization, an increase in the annealed samples' transparency and haze <10 % is reported 41,[195][196][197][198] . Different derivates of N,N',N''-alkyl and N,N',N''-aryl-1,3,5benzenetricarboxylamides are also shown to act as a clarifiers due to the formation of smaller crystals [199][200][201][202][203][204] .…”

Development of a Biomass Furan-Hydrazide Nucleating Agent of Poly(l-lactide) and Its Application for Biaxial-Oriented Films with Enhanced Performance

“…Another extensively studied category of organic NAs includes amides and hydrazides. These agents play a pivotal role in nucleation by facilitating the formation of helical structures within PLLA through intermolecular interactions between imino groups and PLLA’s carbonyl groups, resulting in a significantly enhanced promotion of crystallization. − For instance, Cai et al synthesized and investigated aromatic hydrazide NAs, namely, N , N ′-bis (salicyloyl) p -phthalic acid dihydrazide. The hydrogen bonding between NA’s hydroxyl group and PLLA’s carbonyl group adsorbs the PLLA chains on its surface.…”