Macrocyclic oligomers as compatibilizing agent for hemp fibres/biodegradable polyester eco-composites

Abstract

Ring:chain equilibria (RCE), existing under appropriate reaction conditions, between a linear polyester and the corresponding family of macrocyclic oligomers (MCOs), were exploited to develop an original compatibilizing pathway for preparing eco-composites based on hemp fibres and a biodegradable random co-polyester, namely poly(1,4-butylene adipate-co-terephthalate) (PBAT) with 50:50 adipate:therephthalate proportion. Cyclo-depolymerization (CDP) of PBAT was successfully carried out at high dilution using various solvents, catalysts, and reaction times. The reconversion of MCOs into linear chains by entropically-driven ring-opening polymerization (ED-ROP) occurs by simple heating in the bulk. This reaction, after optimization of catalyst amount, temperature, and reaction time, was used for the surface modification of hemp fibres. PBAT-based eco-composites containing hemp fibres as such or pre-modified by treatment with the MCOs were then prepared and characterized by morphological and mechanical analysis.

ED-ROP of macrocyclic oligomers: A synthetic tool for multicomponent polymer materials

“…106 Taking into account what said above and notwithstanding the advantages that ED-ROP of low-melting MCOs could offer in preparing NFRCs, very few examples are reported in the literature on this topic. [107][108][109] Romão et al 107,108 produced pCBT-based composites with 32 vol% of flax fiber fabric by TP-RTM technique. Commercial CBT were infused in a closed mold containing the dry fiber pre-form.…”

“…The authors ascribed the brittleness to the high crystallinity of formed pCBT resin, as determined by DSC analysis, while the poor fiber-polymer adhesion was attributed to the absence of a suitable fiber compatibilization treatment. In a recent work Conzatti et al 109 achieved "fully green" eco-composites, that is constituted of a biodegradable polyester matrix, namely poly(1,4butylene adipate-co-terephthalate) (PBAT), reinforced with raw hemp fibers from agricultural wastes. MCOs of PBAT (CBAT, see Chart 1) were, for the first time, successfully prepared in quantitative yields by CDP reaction in mild conditions and exploited as a suitable coupling agent between the PBAT matrix and hemp fibers.…”

Plant Fibers-Based Sustainable Biocomposites

“…Influence of hemp fibers on the behavior of hemp-PP composites was examined at controlled temperature under uniaxial tensile loading at different strain rates [88]. The natural fibres reinforced with biodegradable polymers result in completely "green" composites like hemp/PLA [89], hemp/polybenzoxazine [90], and hemp/ polyester [91].…”

Green Degumming Technology of Hemp and a Comparison between Chemical and Biological Degumming

“… 3 , 4 It is necessary to release the fiber from “the bound state” by degumming treatment, which is a vital process for its production, as shown in Figure 1 . 5 , 6 The traditional chemical degumming of hemp fiber is done mainly with sodium hydroxide, uses strong acid and alkali as the steaming solution, and also requires high-temperature and high-pressure steaming conditions. 7 , 8 The hemp fiber fabric prepared by the above-mentioned traditional chemical degumming has the complicating problems of rough texture, non-ideal performance, and serious pollution.…”