N2O–Assisted Siphon Foaming of Modified Galactoglucomannans With Cellulose Nanofibers

Foaming of most bio-based polymers is challenged by low pore formation and foam stability. At the same time, the developing utilization of bio-based materials for the circular economy is placing new demands for easily processable, low-density materials from renewable raw materials. In this work, we investigate cellulose nanofiber (CNF) foams in which foaming is facilitated with wood-based hemicelluloses, galactoglucomannans (GGMs). Interfacial activity of the GGM is modulated via modification of the molecule’s amphiphilicity, where the surface tension is decreased from approximately 70 to 30 mN m−1 for unmodified and modified GGM, respectively. The chemical modification of GGMs by substitution with butyl glycidyl ether increased the molecule’s hydrophobicity and interaction with the nanocellulose component. The highest specific foam volume using 1 wt% CNF was achieved when modified GGM was added (3.1 ml g−1), compared to unmodified GGM with CNF (2.1 ml g−1). An amount of 96 and 98% of the GGM and GGM-BGE foams were lost after 15 min of foaming while the GGM and GGM-BGE with cellulose nanofibers lost only 33 and 28% of the foam respectively. In the case of GGM-BGE, the foam stability increased with increasing nanofiber concentration. This suggests that the altered hydrophobicity facilitated increased foam formation when the additive was incorporated in the CNF suspension and foamed with nitrous oxide (N2O). Thus, the hydrophobic character of the modified GGM was a necessity for foam formation and stability while the CNFs were needed for generating a self-standing foam structure.

Selective Extraction of Nonfullerene Acceptors from Bulk-Heterojunction Layer in Organic Solar Cells for Detailed Analysis of Microstructure

Detailed analyses of the microstructures of bulk-heterojunction (BHJ) layers are important for the development of high-performance photovoltaic organic solar cells (OSCs). However, analytical methods for BHJ layer microstructures are limited because BHJ films are composed of a complex mixture of donor and acceptor materials. In our previous study on the microstructure of a BHJ film composed of donor polymers and fullerene-based acceptors, we analyzed donor polymer-only films after selectively extracting fullerene-based acceptors from the film by atomic force microscopy (AFM). Not only was AFM suitable for a clear analysis of the morphology of the donor polymers in the BHJ film, but it also allowed us to approximate the acceptor morphology by analyzing the pores in the extracted films. Herein we report a method for the selective extraction of nonfullerene acceptors (NFAs) from a BHJ layer in OSCs and provide a detailed analysis of the remaining BHJ films based upon AFM. We found that butyl glycidyl ether is an effective solvent to extract NFAs from BHJ films without damaging the donor polymer films. By using the selective extraction method, the morphologies of NFA-free BHJ films fabricated under various conditions were studied in detail. The results may be useful for the optimization of BHJ film structures composed of NFAs and donor polymers.

Structural Composition Explains Differences in Stretchability for Compression-Molded Arabinoxylan-Based Thermoplastic Films

<div><div><div><p>Valorization of argi-waste polymers into value-added materials is essential for sustainable development of polymeric industry. Reported herein is a 1-step and 2-step strategy for fabrication of flexible and stretchable thermoplastics prepared by compression molding from two structurally different arabinoxylans (AX). The synthesis was accomplished using n-butyl glycidyl ether whose epoxide ring opened on hydroxyl group and resulted in introduction of alkoxide sidechains for the 1-step synthesis. AX was preactivated by periodate oxidation as 1st step for the 2-step synthesis. Two structurally different AXs, i.e. wheat bran extracted arabinoxylan (AXWB, araf/xylp=3/4) and barley husk extracted arabinoxylan (AXBH, araf/xylp=1/4) were used to understand the effects of the araf/xylp on thermoplastic properties because melt processability has been rare for low araf/xylp AXs. AXBH-derived samples demonstrated melt compression processability. AXWB and AXBH derived thermoplastics featured dual and single glass transition (Tg) characteristics respectively as confirmed by DSC and DMA, but AXBH derived thermoplastics had lower stretchability (maximum 160%) compared to AXWB samples (maximum 300 %). Higher araf/xylp and thus in turn longer alkoxide side chains in AXWB derived thermoplastics explained differences in stretchability.</p></div></div></div>

Structural Composition Explains Differences in Stretchability for Compression-Molded Arabinoxylan-Based Thermoplastic Films

<div><div><div><p>Valorization of argi-waste polymers into value-added materials is essential for sustainable development of polymeric industry. Reported herein is a 1-step and 2-step strategy for fabrication of flexible and stretchable thermoplastics prepared by compression molding from two structurally different arabinoxylans (AX). The synthesis was accomplished using n-butyl glycidyl ether whose epoxide ring opened on hydroxyl group and resulted in introduction of alkoxide sidechains for the 1-step synthesis. AX was preactivated by periodate oxidation as 1st step for the 2-step synthesis. Two structurally different AXs, i.e. wheat bran extracted arabinoxylan (AXWB, araf/xylp=3/4) and barley husk extracted arabinoxylan (AXBH, araf/xylp=1/4) were used to understand the effects of the araf/xylp on thermoplastic properties because melt processability has been rare for low araf/xylp AXs. AXBH-derived samples demonstrated melt compression processability. AXWB and AXBH derived thermoplastics featured dual and single glass transition (Tg) characteristics respectively as confirmed by DSC and DMA, but AXBH derived thermoplastics had lower stretchability (maximum 160%) compared to AXWB samples (maximum 300 %). Higher araf/xylp and thus in turn longer alkoxide side chains in AXWB derived thermoplastics explained differences in stretchability.</p></div></div></div>

Enantioselective terpolymerization of racemic andmeso-epoxides with anhydrides for preparation of chiral polyesters

The preparation of stereochemistry- and sequence-defined polymers, in which different monomer units are arranged in an ordered fashion just like biopolymers, is of great interest and has been a long-standing goal for chemists due to the expectation of unique macroscopic properties. Here, we describe the enantioselective terpolymerization of racemic terminal epoxides,meso-epoxides, and anhydrides mediated by the privileged chiral dinuclear Al(III) catalyst system, to afford optically active polyester terpolymers with either gradient or random distribution as determined by the epoxides employed during their preparation. The enantioselective terpolymerization of racemictert-butyl glycidyl ether (rac-TBGE) and cyclopentene oxide with phthalic anhydride (PA) or naphthyl anhydride (NA) gives novel gradient polyesters, in which the crystallization behavior varies continuously along the main chain, due to the decrement of one ester component and the increment of the other occurring sequentially from one chain end to the other. In contrast, the enantioselective terpolymerization ofrac-TBGE andmeso-epoxide (cyclohexene oxide, 3,4-epoxytetrahydrofuran, or 1,4-dihydronaphthalene oxide) with an anhydride (PA or NA) provided chiral statistical terpolyesters with the random distribution of two kinds of ester units, resulting in a material possessing a mixed glass transition temperature. The present study therefore provides a convenient route to chiral polyesters bearing a range of physical and degradability properties.

Effect of a Healing Agent on the Curing Reaction Kinetics and Its Mechanism in a Self-Healing System

Self-healing cementitious composites have been developed by using microcapsules. In this study, the effect of the healing agent on the crosslinking and curing reaction kinetics was analyzed. The effect of the diluent n-butyl glycidyl ether (BGE) on the reaction was investigated for five fractions, namely 10.0%, 12.5%, 15.0%, 17.5%, and 20.0% mass fractions to epoxy resin. The Kissinger and Crane equations were used to obtain the activation energy and reaction order with different mass fractions of diluent, as well as the kinetic parameters of the curing reaction. The optimal fraction of BGE was determined as 17.5%. Likewise, the effect of the curing agent MC120D on the reaction kinetics was investigated for 10%, 20%, 30%, 40%, and 50% mass fractions to the diluted epoxy resin. The optimal fraction was determined as 20%. The mechanism of the curing reaction with the healing agent was investigated. The infrared spectra of the cured products of 20% MC120D with BGE/E51 (0.0%, 12.5%, 15.0%, 20.0%, 100%) were analyzed. It is shown that not only the epoxy resin E-51 was cured, but also that the BGE was involved in the cross-linking reaction of the epoxy resin E-51 with MC120D.