Poly(ε-caprolactone) Biocomposites Based on Acetylated Cellulose Fibers and Wet Compounding for Improved Mechanical Performance

Abstract

Poly(ε-caprolactone) (PCL) is a ductile thermoplastic, which is biodegradable in the marine environment. Limitations include low strength, petroleum-based origin, and comparably high cost. Cellulose fiber reinforcement is therefore of interest although uniform fiber dispersion is a challenge. In this study, a one-step wet compounding is proposed to validate a sustainable and feasible method to improve the dispersion of the cellulose fibers in hydrophobic polymer matrix as PCL, which showed to be insensitive to the presence of the water during the processing. A comparison between unmodified and acetylated cellulosic wood fibers is made to further assess the net effect of the wet feeding and chemical modification on the biocomposites properties, and the influence of acetylation on fiber structure is reported (ATR-FTIR, XRD). Effects of processing on nanofibrillation, shortening, and dispersion of the cellulose fibers are assessed as well as on PCL molar mass. Mechanical testing, dynamic mechanical thermal analysis, FE-SEM, and X-ray tomography is used to characterize composites. With the addition of 20 wt % cellulosic fibers, the Young's modulus increased from 240 MPa (neat PCL) to 1850 MPa for the biocomposites produced by using the wet feeding strategy, compared to 690 MPa showed for the biocomposites produced using dry feeling. A wet feeding of acetylated cellulosic fibers allowed even a greater increase, with an additional 46% and 248% increase of the ultimate strength and Young's modulus, when compared to wet feeding of the unmodified pulp, respectively.

Substantial Effect of Water on Radical Melt Crosslinking and Rheological Properties of Poly(ε-Caprolactone)

“…This is consistent with the gel content results (at 1 wt.% peroxide). It is worth to note that large presence of water (>50 wt.%) in PCL melt processing does not significantly decrease its molecular weight due to water-induced hydrolysis [ 41 ].…”

A Review of Wet Compounding of Cellulose Nanocomposites

“…Twin screw extrusion is the most commonly used method for the wet compounding of cellulose nanocomposites [ 6 , 9 , 12 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ]. Extruders are widely available and typically have multiple zones that can individually be tailored for mixing intensity, temperature, venting, etc., making them very adaptable.…”

“…The tensile properties of the composites produced were much higher than those produced by dry feeding, increasing the modulus and strength by 213% and 71%, for unmodified cellulose. Even higher improvements were found when acetylated fiber was used [ 42 ]. However, fibers were not of nanoscale dimensions and long processing times (20 min of recirculation) were used, partly due to the limited shearing capabilities of the microcompounder used.…”

“…For example, Peng et al reported melt extrusion of PA6 with and without water led to reductions in molecular weight of 13% and 9.5%, respectively, a difference of less than 4% [ 6 ]. Lo Re et al also reported minimal change to the molecular weight of PCL when wet compounded with cellulose [ 42 , 62 ], and in one case, the maximum reduction was less than 5% even when compounded up to 30 min or with up to 41% initial water content [ 42 ]. Peng et al [ 6 ] also reported that water led to the nucleation of alpha phase crystal structure of PA6, which favorably affected the mechanical properties of PA6, even in the absence of CNCs.…”

Surface modification effects on nanocellulose – molecular dynamics simulations using umbrella sampling and computational alchemy

“…In this context, controlled acetylation resulted in increased cellulose thermostability and melt-processed biocomposites with improved cellulose dispersion and thermomechanical performance. (27,28,29) The purpose of the present study is to investigate some of the mechanisms for acetylation effects in the context of cellulose nanocomposites and nanomaterials. The possibilities to predict the outcome of topochemical modification are limited due to the inherent nanoscale of the problem.…”