Properties of Bioplastics

• Water insolubility is the most important property that differentiates them from other currently available biodegradable plastics.

• They have good oxygen permeability and UV resistance. Good biocompatibility makes them suitable for medical applications.

• Homo-polymer of Polyhydroxybutyrate is melt processable with a melting point of 185°C and glass transition temperature (Tg) of -4°C.The properties of Polyhydroxybutyrate copolymers can be tailored from hard and brittle to soft and flexible by varying the copolymer composition. Its physical properties are comparable to conventional polymers which makes it suitable to a variety of commodity applications.

• Due to their ability to degrade naturally in variety of environments without leaving any toxic residues to environment, they will find a variety of applications in disposal items such cups, containers as well packaging and agricultural mulching films to list a few.

2. Polylactic Acid :

PLA has different forms such as:
i. Poly-L-lactide (PLLA)
ii. Poly-D-lactide (PDLA)

• PLLA has crystallinity of approx. 37%, glass transition temperature (Tg) 50-80° C and melting temperature (Tm) between 175-185 °C. (Amorphous PLA’s have relatively lower Tg and Tm than semi-crystalline PLA’s)

• PDLA is generally blended with PLLA to improve thermal properties and increase crystallinity which increases rate of crystallization. PDLA offers useful property of being optically transparent. Also due to its higher crystallinity, its biodegradation rate is slower than PLA.

• Due to low melting points, doesn’t yet have as many applications as conventional plastics like PET.

• PLA has high mechanical strength, thermal plasticity, fabricability, biodegradability, and biocompatibility.

• Under identical processing conditions semi-crystalline PLA has a higher shear viscosity than amorphous PLA due to the differences in their molecular structures.

3. Polycaprolactone:

• The polymer has melting point of approximately 60° C and a glass transition temperature of approximately -60° C

• It has physical properties of a very tough, nylon-like plastic that melts to a putty-like consistency at only 60°C. However, it has limited heat resistance.

• Though it is based on petroleum resources it is readily degradable and mineralized by various microorganisms. The common degradation mechanism is hydrolysis of ester linkages in the polymer.

4. Polyvinyl Alcohol :

• PVA has a melting point range of 190-230°C which depends on different grades of the polymer that are based on ability to undergo hydrolysis.

• It has excellent film forming, emulsifying and adhesive properties. Also its properties depend on the molecular weight and the degree of hydrolysis.

• It is a strong polymer with high tensile strength and flexibility as well as good oxygen barrier properties. However, as the humidity increases, this polymer absorbs more water which acts as a plasticizer and reduces tensile strength, but increases the tear strength and elongation.

• Although it’s found to be biodegradable in several environments, most of the work has been conducted on water soluble PVA.