ABSTRACT:

This First Year Assesment is focused on the development of biodegradable self-feinforced composites to be used in biomedical applications. Self-reinforced composites are considered a new class of composites in which a single type of polymer (or family) acts as both reinforcement and matrix. Such composite textiles emerged as potential candidates for lightweight applications exhibiting excellent mechanical performance.
The self-reinforced composites used in this work were produced by hot consolidation of dry textiles that were previously weaved by using commingling yarns. Such type of commingling yarns are produced by combination of two types of polymer fibers that may differ slightly in its chemical composition, structure and thermal behavior. During the first stages of the project, it was intended to produce self-reinforced composites with PLLA (Poly L-lactic acid) and PLA (Polylactic acid) fibers. However, PCL (Polycaprolactone) fibers were used instead due to the scarcity of PLLA fibres with high melting temperature. Both PLLA and PCL are biodegradable materials, which are also approved by Food and Drugs Administration (FDA)for medical purposes.

The manufacturing process for producing the self-reinforced PLA-PLA and PLA-PCL composites is based on hot-press of textiles weaved by using commingling PLA-PLA and PLA-PCL yarns. They were produced with PLA fibers with two slightly different melting temperatures in the case of the PLA-PLA textiles. The manufactured mateirals were characterized in terms of thermal properties by means differential scanning calorimetry (DSC), microstructure (ultrasound inspection and optical/scanning electron microscopy (SEM)) and mechanical performance through tensile test of coupons extracted from the consolidated panels. No single laminate was able to fulfil all the requirements, and it was necessary to compromise the process in function of the priority property. The hot-press manufacturing cycle was optimised in terms of hold time, consolidation pressure and consolidation temperature to maximise the mechanical performance (strength and toughness).

For the PLA-PLA laminates, a processing cycle consisting in applying 2 MPa of compaction pressure at 155 C during 10 minutes was enough to ensure laminates almost free of porosity with elastic modulus and tensile strength of 4.09± 0.24 GPa and 30.39±1.21 MPa, respectively. However, the PLA-PCL composites did not lead to laminates free of porosity as the proportion of PCL fibers in the PCL/PLA commingled yarn was not enough to ensure its role as matrix in the self-reinforced composite. These porous PCL-PLA composites could be tailored – through an adequate control of the consolidation