Aligned unidirectional PLA/bacterial cellulose nanocomposite fibre reinforced PDLLA composites

Abstract

In an effort to enhance the properties of polylactide (PLA), we have developed meltspinning techniques to produce both PLA/nanocellulose composite fibres, and a method akin to layered filament winding followed by compression moulding to produce self-reinforced PLA/nanocellulose composites. Poly(L-lactide) (PLLA) fibres were filled with 2 wt.% neat and modified bacterial cellulose (BC) in an effort to improve the tensile properties over neat PLA fibres. BC increased the viscosity of the polymer melt and reduced the draw-ratio of the fibres, resulting in increased fibre diameters. Nonetheless, strain induced chain orientation due to melt spinning led to PLLA fibres with enhanced tensile modulus (6 GPa) and strength (127 MPa), over monolithic PLLA, previously measured at 1.3 GPa and 61 MPa, respectively. The presence of BC also enhanced the nucleation and growth of crystals in PLA. We further produced PLA fibres with 7 wt.% cellulose nanocrystals (CNC), which is higher than the percolation threshold (equivalent to 6 vol.%). These fibres were spun in multiple, alternating controlled layers onto spools, and subsequently compression moulded to produce unidirectional self-reinforced PLA composites consisting of 60 2 vol.% PLLA fibres reinforced with 7 wt.% CNC in a matrix of amorphous PDLLA, which itself contained 7 wt.% of CNC. We observed improvements in viscoelastic properties of up to 175% in terms of storage moduli in bending. Furthermore, strains to failure for PLLA fibre reinforced PDLLA were recorded at 17%.

Composition dependence of the synergistic effect of nucleating agent and plasticizer in poly(lactic acid): A Mixture Design study

“…Nano-fillers, such as cellulose nano-whiskers [26], carbon nano-tubes [27] or graphene oxide [28] were also reported to act as nucleating agents for PLA, although composition and geometrical characteristics of the nano-fillers were reported to have a strong effect on overall crystallization rate. In general, a planar structure in organic molecules or rigid surface in nano-fillers and also groups interacting with polyester chains (also leading to chain scission [21]) are characteristics typical of all the effective nucleating agents, indicating that both the formation of specific directional linkages or confinement effects can affect the mobility and orientation at a molecular scale, thus influencing crystals formation.…”

In situ processing of cellulose nanocomposites

“…BC has been used as reinforcement in different polymeric matrices such as cellulose acetate butyrate, polylactic acid, polyhydroxy butyrate, starch, hydroxyl ethyl cellulose, polyvinyl alcohol, acrylic resin, epoxidised soyabean oil etc [17,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. In the ex situ synthesis of BC nanocomposites the penetration of the second component through the BC network may not be uniform which results into a non-homogeneous structure.…”

Multi-layer nanopaper based composites

“…During the last decades natural fiber composites have gained renewed attention due to environmental issues associated with conventional composites produced from synthetic materials (Moon et al 2011;Blaker et al 2014;Mariano et al 2014). Even though progress was made in recycling of high performance composites, these types of materials still pose significant waste issues (Montrikittiphant et al 2014;Pimenta and Pinho 2011).…”