Manufacturing and Characterization of Highly Environmentally Friendly Sandwich Composites from Polylactide Cores and Flax-Polylactide Faces

Abstract

This work focuses on the manufacturing and characterization of highly environmentally friendly lightweight sandwich structures based on polylactide (PLA) honeycomb cores and PLA-flax fabric laminate skins or facings. PLA honeycombs were manufactured using PLA sheets with different thicknesses ranging from 50 to 500 μm. The PLA sheets were shaped into semi-hexagonal profiles by hot-compression molding. After this stage, the different semi-hexagonal sheets were bonded together to give hexagonal panels. The skins were manufactured by hot-compression molding by stacking two Biotex flax/PLA fabrics with 40 wt% PLA fibers. The combined use of temperature (200 °C), pressure, and time (2 min) allowed PLA fibers to melt, flow, and fully embed the flax fabrics, thus leading to thin composite laminates to be used as skins. Sandwich structures were finally obtained by bonding the PLA honeycomb core with the PLA-flax skins using an epoxy adhesive. A thin PLA nonwoven was previously attached to the external hexagonal PLA core, to promote mechanical interlock between the core and the skins. The influence of the honeycomb core thickness on the final flexural and compression properties was analyzed. The obtained results indicate that the core thickness has a great influence on the flexural properties, which increases with core thickness; nevertheless, as expected, the bonding between the PLA honeycomb core and the skins is critical. Excellent results have been obtained with 10 and 20 mm thickness honeycombs with a core shear of about 0.60 and facing bending stresses of 31–33 MPa, which can be considered as candidates for technical applications. The ultimate load to the sample weight ratio reached values of 141.5 N·g−1 for composites with 20 mm thick PLA honeycombs, which is comparable to other technical composite sandwich structures. The bonding between the core and the skins is critical as poor adhesion does not allow load transfer and, while the procedure showed in this research gives interesting results, new developments are necessary to obtain standard properties on sandwich structures.

Environmentally Friendly Polymer Compositions with Natural Amber Acid

“…The second polymer used in the research, aliphatic polyester (PHA), was purchased from Simag Holdings LTD (Hong Kong, China). Polymeric materials PHA had the following properties: P(3,4HB) containing 12 mol% 4-hydroxybutyrate, the average fold was approximately 520 kDa, MVR = 15-20 g/10 min, (assay conditions: temperature 170 • C, nominal load 2.16 kg) and a density of 1.25 g/cm 3 . Polymers from the group of polyhydroxyalkanoates are synthesized by some bacteria as intracellular storage compounds.…”

“…Nowadays, environmentally friendly and biodegradable polymer compositions are an important aspect of scientists' research. Particularly noteworthy are polymers of natural origin, such as materials made of plant starch (e.g., polylactide), bacterial polymers (polyhydroxyalkanoates), cellulose, and compositions based on shellac, zein and other pro-ecological ingredients [1][2][3][4][5].…”

Peroxide-Induced Synthesis of Maleic Anhydride-Grafted Poly(butylene succinate) and Its Compatibilizing Effect on Poly(butylene succinate)/Pistachio Shell Flour Composites

“…This low compatibility between both composite components then affects the filler-matrix interfacial adhesion, which can result in poor filler dispersion and large particle agglomeration, both being detrimental for the mechanical performance of the polymer composites. Furthermore, the presence of the hydrophilic fillers frequently promotes undesirable water uptake phenomena that can cause dimensional changes and ageing in the polymer composites [ 32 ]. As a result, different strategies have been used to enhance interfacial adhesion in polymer composites, improving their final properties [ 33 ].…”

Free vibration analysis of a skew sandwich plate with bamboo biocomposite and polylactic acid core under temperature and moisture conditions

“…It is gaining importance in numerous systems consisting of composite sandwich structures like 3D-printed honeycomb cores and skin on various composite panels. 38 Lascano et al 39 studied the fabrication and mechanical characterization of the laminated composite sandwich (LCS) plate with flax/PLA face-sheet and PLA as the core.…”