Bio-Polyester-Date Seed Powder Composites: Morphology and Component Migration

Biodegradable polyesters poly-l-lactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) were reinforced with varying amount of date seed powder (DSP) with an aim to utilize the date seed waste as well as to achieve composites with improved properties. The PLA composites exhibited increase in the elastic response over the viscous response as a function of filler fraction, whereas the PBAT composites retained the viscous dominance irrespective of DSP content. The tensile modulus of the PBAT composites had enhancement of more than 300% in the composite with 40% filler content. The PLA composites also enhanced the modulus marginally till 20% filler content, however, it was still significant because of the very high modulus of PLA as compared to PBAT. Thermal analysis also indicated the stability of the composite, thus, confirming the usefulness of DSP as filler for the polymers. The TEM and light microscopy characterization revealed presence of voids in the composites which were present around the filler particles as well as dispersed in the polymer matrix. Such features were confirmed through TGA-MS to be resulting from the escape of water vapor bound in DSP. The composites with 10% DSP content had lower extent of such voids and the morphology remained relatively unchanged with time. In the composites with 30% DSP content, in the seasoned sample, a soft and sticky phase resulting from the surface migration of date seed oil was also observed. The generation of the soft phase was also a slow process as 24 h were not enough to generate this phase. The migration of the oil to the surface was also confirmed by the IR and X-ray diffraction studies. After embedding in compost soil, the PLA composite with 40% filler content had nine times more biodegradation after 120 days as compared to pure polymer, whereas it was 11 times for PBAT composite with same filler content. It confirmed that the addition of DSP did not lead to any thermal and mechanical degradation of the bio-polyesters and resulted in enhanced mechanical and biodegradation behavior along with oil migration. The controlled component migration can lead to potential generation of commercially important self-lubricating composite materials. POLYM. ENG. SCI., 55:877-888, 2015. (c) 2014 Society of Plastics Engineers