Bio-Plastics Bio-based Plastics Major focus is on “origin of life” or where did Carbon come from.. Biodegradable Plastics Focus is on “end of life or disposal” Defined by EN13432 and ASTM D6400
What are Biodegradableplastics? Biodegradable or Compostable plastics are those that meet all the scientifically recognized standards of biodegradability of plastics and plastic products independent of their carbon origin. According to ASDM D6400, biodegradability is measured on Mineralization, Disintegration and Safety of the material. - atleast 90% conversion to CO2, water and biomass via microbial assimilation. - should occur within a time period of 180 days or less. - no impacts on plants. - etc……
Drivers for Bioplastics Reduced environmental impact. Disposal issues – Landfills. Concerns about human health. Legislative initiatives.
Starch and Starch blends Virgin starch is brittle and difficult to be processed. This problem is mainly caused by the presence of strong inter‐ and intra‐ molecular hydrogen bonds between the starch macromolecules. Thermoplasticized starch Cross-linked starch Starch esters Starch – Biopolymer blends
High density Low resistance to oil and solvents Easy to process bur vulnerable to degradation. Sensitive to moisture High water vapour permeability
Cellulose based Bioplastics Cellulose-based bioplastics are typically chemically- modified plant cellulose materials such as cellulose acetate (CA). Common cellulose sources include wood pulp, hemp and cotton. These biodegradable plastics can be processed on conventional injection molding machines or on extruders adapted to their specific processing properties. The thermal resistance is somewhat lower, but the permeability to steam and oxygen is relatively high compared to that of standard plastics. The material is resistant to oils and fats and, for a short while, even to weak acids and alkalies.
Polylactic Acid (PLA) PLA is an aliphatic polyester. The conformational ratio of L- and D- lactic acid in the polyester decides the material properties. Degrades within 4 to 6 weeks . High stability Transparency
The biology ofPolyhydroxyalkanaotes (PHA) The carbon sources are assimilated, converted into hydroxyalkanoate (HA) compounds and finally polymerized into high molecular weight PHAs and stored as water insoluble granules in the cell cytoplasm. PHAs are an excellent storage compound because their presence in the cytoplasm, even in large quantities does not disturb the osmotic pressure of the cell. These granules may be surrounded by a phospholipid monolayer that contains specific granule associated proteins. PHA granules are intriguingly maintained in an amorphous state in vivo.
A) Transmission Electron micrograph of Ralstonia eutropha H16 containing 70 wt% P(3HB) granules cultured in mineral medium containing palm kernel oil as the sole carbon source for 48h.B) Nile Blue stained R. eutropha cells containing P(3HB) granules cultivated for 72h in mineral medium containing palm kernel oil as the sole carbon source.
Chemical Composition ofPHAs approximately 150 different constituents of PHAs have been identified as homopolymers or as copolymers.
Good thermoplastic material. Wide temperature range Lower crystallinity Tendency of shrinkage UV resistance
• Short chain-length PHAs (SCL-PHA): contains 3-5 carbon atoms. Monomer size • Medium chain-length PHAs (MCL- PHA): contains 6-14 carbon atoms • Homopolymer: The polymerization begins with the linkage of a small molecule or monomer through esterNumber of different bonds to the carboxylic group of the next monomer. A homopolymer is produced when single monomeric units are linked together. i.e P(3HB).monomers in PHAs • Heteropolymer: When two or more different monomeric units are linked together, a copolymer is formed. i.e P(3HB-co-4HB). • Natural PHAs: produced naturally by microorganisms from general substrates. i.e Poly(3- hydroxybutyrate) P(3HB)Biosynthetic origin • Semisynthetic PHAs: requires addition of unusual precursors such as 3-mercaptopropionic acid to promote the biosynthesis of poly(3-hydroxybutyrate- co-3-mercaptopropionic) [P(3HB-co-3MP)]
Wild type and recombinant strains used for pilot and large scale production of PHA
Strain and Process Development for industrial production of PHA
Comparison of mechanical properties of different PHAs with common plastics
In general SCL PHAs are highly crystalline and have poor tensile strength. MCL PHAs are amorphous and very elastomeric. P(3HB-co-3HHx) is an interesting copolymer. 3HHx units addition(5 mol%) into the 3HB sequence reduces the melting point from 180 °C to less than 155 °C, thus significantly improving the thermal processability and physical properties. Aeromonas caviae and A. hydrophila are the only found organisms to naturally produce this polymer.
Applications of PHA in various fields All materials for short life packing likePackaging Industry food utensils, films, electronic appliancesPrinting and Photography PHA are polyesters that can be easily stained.Chemical Industry Heat sensitive matrices, latex gels. Nonwoven matrices to remove facial oil.Textile Industry PHA can processed into fibers.Medical Implants Medical implant materials, drug controlled release matrices.Healthy food additives PHA oligomers used as food supplements to obtain ketone bodies.Biofuels & additives Hydrolysed to form combustible HA methyl esters.Protein Purification & PhaP used to purify recombinantSpecific Drug delivery proteins and along with specific ligands, can achieve targeting to dieseased tissue.
Advantages Lower fossil fuels consumption. Less dependency on non-renewable resources. Lower CO and other green house gas 2 emissions in the atmosphere. Decrease in waste generation. Water saving.
Disadvantages Bio-based plastics are made from plant sources like corn and maize. With already increasing demand of food supply, Plastic production from plants could create a steep cut-short. Some bioplastics don’t readily decompose. They require high temperature in especially built pilot plants. Thus, they may not be so economical. GMOs are used to increase productivity of PHA and PLA.
Future developments prospects High cell density within short period of time. Controllable lysis of cells containing PHA granules. Controllable PHA molecular weight. Use of PHA monomers as biofuels additives. PHA blending with starch, cellulose. PHA as building blocks for new polymers.
References Lei Pei et al, Biotechnology of Biopolymers, 2010. Guo-Qiang Chen, Chemical Society Reviews, 2009. Ching-Yee Loo and Kumar Sudesh, Malayasian Polymer Journal, 2007. Erwin T.H. Vink et al, Polymer degradation and stability, 2002. Franziska Hempel et al, Microbial Cell Factories, 2011. bioplastics MAGAZINE www.bioplasticsmagazine.com/
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