240 Introduction to Renewable Biomaterials
During last decades, many researches have also studied composites with natural fillers.
These works allowed obtaining composites with reduced environmental impact, using
renewable sources as fillers, and renewable sources or not as matrices.
The first part of this chapter focuses on the main feature of oil-based and bio-derived
thermoplastic polymers and their blends, while the second part covers composites with
natural fillers.
Composites 8 Oil-Based and Bio-Derived Thermoplastic Polymer Blends and
8.2.1 Comparison Between Oil-Based and Bio-Derived Thermoplastic Polymers
Bio-derived thermoplastic polymers were developed during last decades in order to
potentially substitute traditional polyolefins in their common applications such as
- packaging and food (films, containers, food wrapper, composting bags, plates, cutlery)
- agricultural (planting containers, controlled release of chemicals)
- textile (wipes, filters, geotextiles, diapers)
- medicine (release of drugs, suture, screw, orthopaedic products).
The importance of bio-based polymers in these fields concerns the reduction of envi-
ronmental impacts and the improved compatibility with organic material. Nevertheless,
hydrophilicity of bio-based polymers can be a problem, concerning the compatibility
with traditional hydrophobic polyolefins.
Polylactic acid (PLA) is one of the most known bio-derived polymer first produced
through polymerization by Carothers in 1932 [1] and lately patented by DuPont in 1954.
PLA is an aliphatic thermoplastic polyester generally produced through ring-opening
polymerization of lactides.
Mechanical properties of PLA are good considering the tensile modulus, tensile
strength and flexural strength, comparable or higher than traditional polyolefins such
as polyethylene, polypropylene and polyethylene terephthalate. Table 8.1 reports the
main mechanical features of PLA and traditional polyolefin.
Otherwise, one of the main drawbacks of PLA is its brittleness; in fact tensile modulus
and tensile strength of PLA are comparable to PET, but PLA elongation at break limited
its applications in PET fields [2].
In order to improve PLA applications, brittleness has to be decreased. During the last
years, researchers proposed different ways to face this problem, such as biocompatible
Table 8.1Some PLA mechanical features in comparison to traditional
polyolefin.
PLA PET HDPE PP
Tensile modulus (GPa) 3.4 3.3 1.3 1.8
Tensile strength (MPa) 53 50–70 15–20 40–50
Flexural strength (MPa) 80 80 20 40
Elongation at break (%) 6 50–150 700–800 100–600
Cost ($/lb) 1–1.5 0.70–0.72 0.27 0.28
