Improved mechanical properties of polylactide nanocomposites-reinforced with cellulose nanofibrils through interfacial engineering via amine-functionalization

Abstract

One of the main factors responsible for the mechanical and physical properties of nanocomposites is the effectiveness of the interfacial region to transfer loads and mechanical vibrations between the nano-reinforcements and the matrix. Surface functionalization has been the preferred approach to engineer the interfaces in polymer nanocomposites in order to maximize their potential in structural and functional applications. In this study, amine-functionalized cellulose nanofibrils (mCNF-G1) were synthesized via silylation of the hydroxyl groups on the CNF surface using 3-aminopropyltrimethoxysilane (APTMS). To further increase the amine density (mCNF-G2), dendritic polyamidoamine (PAMAM) was grafted onto mCNF-G1 by the Michael addition of methacrylate onto mCNF-G1, followed by the transamidation of the ester groups of methacrylate using ethylenediamine. Compared to native CNF-reinforced, poly(l-lactide) (PLLA) nanocomposites, amine-functionalized CNF exhibited significantly improved dispersion and interfacial properties within the PLLA matrix due to the grafting of PLLA chains via aminolysis. It is also a more effective nucleating agent, with 15% mCNF-G1 leading to a crystallinity of 32.5%, compared to 0.1 and 8.7% for neat PLLA and native CNF-reinforced composites. We have demonstrated that APTMS-functionalized CNF (mCNF-G1) significantly improved the tensile strength compared to native CNF, with 10% mCNF-G1 being the most effective (i.e., >100% increase in tensile strength). However, we also found that excessive amines on the CNF surface (i.e., mCNF-G2) resulted in decreased tensile strength and modulus due to PLLA degradation via aminolysis. These results demonstrate the potential of optimized amine-functionalized CNF for future renewable material applications.

Preparation and properties of poly(lactic acid)/cellulose nanocrystals nanocomposites compatibilized with maleated poly(lactic acid)

“…And addition PEO, a water‐soluble polymer with high molecular weight, into treated CNCs suspension would further improve their thermal stability and obtain the mixture of PEO/CNCs (oCNCs) in which CNCs would well disperse . In order to improve the dispersion and interfacial adhesion in polymeric matrices, various strategies can be used, which include surface modification of CNCs and/or matrix, as well as incorporation of a compatibilizing/coupling agent . While modification of CNCs would have somewhat negative influence.…”

Polylactic acid-lauryl functionalized nanocellulose nanocomposites: Microstructural, thermo-mechanical and gas transport properties

“…Free radical melt grafting of maleic anhydride on the polymer chains of PLA is an efficient and an easy way to improve the compatibility of polymer and different kind of natural fiber from micro to nanometric scale and it was adopted in several studies [38][39][40][41][42][43][44][45]. Amine functionalization of nanocellulose via silanization of the hydroxyl groups on the cellulose surface is an efficient way to improve the dispersion of nanofiller within the polymer and increase the mechanical properties of their relative composited as demonstrated by Lu et al [46]. Ring opening polymerization of L-lactide was employed to functionalize cellulose nanocrystals by Lizundia et al [47] and the obtained functionalized nano crystals were melt-mixed with neat PLA; the extruded biocomposite films exhibited a good interaction and adhesion between filler and the matrix, as demonstrated by the nucleation effect and by the improvement in the strain at break with respect to the neat PLA film.…”

Flame Retardant Polymer Nanocomposites and Interfaces

“…Nanotubes such as carbon nanotube, Halloysite nanotube (HNTs), and cellulose fibers have gained increasing attentions in recent years to replace filler that have high environmental persistence [34][35][36]. They could also render the polymer composite to have increased mechanical properties [37]. When applied in the flame retardant composites, surface modification is commonly used to increase the flame retardancy.…”