Page 352 - Biodegradable Polyesters

330 13 Biodegradable Polyester-Based Blends and Composites

fiber has demonstrated that natural fiber reinforced composites will dominate the
market in many applications.

13.4.3
Polymer–Polymer Composites Based on Biodegradable Polyesters

Although there are a large number of polymer blends available, only those
blends that contain biodegradable polymers and/or natural components are
applicable in the biomedical engineering, particularly in tissue engineering. The
use of biodegradable polymer blends has opened a wide area of study. Different
combination of blends has led to obtain different mechanical properties, which
are indeed very meritorious in medical and other engineering applications.
PHB is an optically active, high-molecular-weight, aliphatic polyester,
biodegradable, and biocompatible, manufactured by microorganisms [67].
PCL/PHB composites are prepared by dissolving PCL and PHB in chloroben-
zene. The mixed composition of PCL and PHB can be molded using compression
molding [68]. These composites exhibit improved mechanical properties, because
PCL enhances the plasticity of the material and PHB contributes to increase
tensile strength [68].
PLA-based composites with polyhedral oligomeric silsesquioxane (POSS) can
be prepared via melt mixing in a twin-screw micro-compounder. The molten,
compounded mixture was molded using an injection molding machine to form the
composite material [69]. The addition of POSS acted as a plasticizer and enhanced
energy absorption capacity. Maximum fracture strength was observed for 7 wt%
addition of POSS in the composites [69].
PLA and PHB could be melt mixed and integrated with D-limonene [68]. PLA
and PHB composites were produced by the film-stacking method, followed by
hot pressing [70]. The incorporation of D-limonene with PLA and PHB results in
the increase of flexibility of composites. Composites made of PLA/PHB showed
higher Young’s modulus when compared to neat plain PLA composites. The
increase in D-limonene content resulted in the decrease of Young’s modulus
and tensile strength. Composites made of PLA–PHB–LIM can be used where
flexibility is an important criterion [70]. PLA/PBS composites have higher tensile
strength and Young’s modulus than those of PLA self-reinforced composites.
The increase in these properties is due to the improved tensile properties of the
PLA film.
PLA can be mixed with natural rubber [71]. PLA and natural rubber are melt
mixed and vacuum dried. The dried blend is cooled to room temperature, and then
chopped into small granules. The composites are obtained by injection molding
[71]. Without any interfacial modification, the transition from brittle to ductile
failure was observed in this blend. The composite made of PLA and natural rubber
blend showed good impact strength when compared to corresponding neat PLA
composites [71].
Poly(R,S-3-hydroxybutyrate) (a-PHB) [72] is synthesized by bulk anionic ring-
opening polymerization by the mixture of R and S isomers of β-butyrolactone