Rapid Solvent-Free Microcrystalline Cellulose Melt Functionalization withl-Lactide for the Fabrication of Green Poly(lactic acid) Biocomposites

Abstract

A green approach is proposed to achieve a rapid surface functionalization of microcrystalline cellulose (MCC) in 30 min by a solvent-free "grafting from" reaction of l-lactide through compression molding without the need for an inert atmosphere. A sufficient hydrophobization of the MCC surface is achieved with an amount of grafted poly­(l-lactic acid) (PLLA) oligomers of 7 wt % with respect to MCC. The obtained MCC-g-PLLA is subsequently melt-compounded with poly­(lactic acid) (PLA) through extrusion and injection molding. As a result of higher compatibility and interfacial adhesion of the functionalized filler with PLA, PLA/MCC-g-PLLA biocomposites with a cellulose content ranging from 4 to 20 wt % exhibit an enhancement in important physicochemical properties (i.e., water vapor barrier, crystallinity, stiffness) compared to both pure PLA and formulations containing an equal or higher amount of nonfunctionalized MCC. At the same time, the materials retain the mechanical strength and resistance to thermal degradation of PLA. The physicochemical characteristics, excellent biocompatibility, and biodegradability of PLA and cellulose and the simplicity, rapidity, and cost-effectiveness of the grafting process render these biocomposites suitable for several applications within the plastics domain including packaging, agriculture, automotive, consumer goods, and household appliances.

Preparation and Characterization of Microcrystalline Cellulose/Polylactic Acid Biocomposite Films and Its Application in Lanzhou Lily (Lilium davidii var. unicolor) Bulbs Preservation

“…Characterization of MCC/PLA Biocomposite Films 3.1.1. SEM Figure 2 illustrated that the morphology of pure PLA surface was uniform and compact, which was consistent with the results reported by Haafiz et al [30] and Genovese et al [22]. The low crystallization ability of pure PLA was responsible for the smooth morphological surface observed.…”

“…The low crystallization ability of pure PLA was responsible for the smooth morphological surface observed. During solvent evaporation, a majority of PLA molecular chains remained in an amorphous state [22]. When used as fillers, MCC exhibited superior cross-linking characteristics and a higher surface area.…”

“…These composites exhibited relatively high levels of transparency and tensile modulus [21]. The functionalized microcrystalline cellulose can improve the compatibility of cellulosic fillers in biopolymer matrices and achieve good dispersion between the hydrophobic PLA matrix and the hydrophilic microcrystalline cellulose filler [22]. Therefore, both cellulose and its derivatives represent a highly valuable filler and exhibit huge potential as alternatives to inorganic materials or other synthetic fiber reinforcements [18,23].…”

Crystallinity-Independent Toughness in Renewable Poly(l-lactide) Triblock Plastics

“…Efforts to simultaneously upgrade PLLA’s thermal and mechanical properties have spawned a rich subfield. Melt-blending with rubbery polymers is the most well-explored approach, owing to the low cost of bulk rubber, translatability to existing melt-processing capabilities, and property tunability under a wide parameter space. , In blends, the most significant mechanical property enhancements most often require reactive − or nonreactive compatibilization. − In other approaches without adding rubber, polymer-grafted cellulose nanocrystals have garnered attention as crystal nucleators , and tougheners. − Amphiphilic non-PLA diblock polymers have also conferred toughness and aging resistance to atactic PLA, − as well as toughness and accelerated crystallization to semicrystalline PLLA. , Finally, thermomechanical preconditioning of PLLA − and its composites can produce highly oriented matrices with improved strength, ductility, and thermal resistance.…”

“…15,16 In blends, the most significant mechanical property enhancements most often require reactive 17−24 or nonreactive compatibilization. 25−30 In other approaches without adding rubber, polymer-grafted cellulose nanocrystals have garnered attention as crystal nucleators 31,32 and tougheners. 33−35 Amphiphilic non-PLA diblock polymers have also conferred toughness and aging resistance to atactic PLA, 36−39 as well as toughness and accelerated crystallization to semicrystalline PLLA.…”