, and , , and are all examples of biopolymers, in which the monomer units. The polymer primary structure is the chemical composition and the sequence in which these units are arranged in. Many biopolymers spontaneously “” into characteristic shapes, which determine their biological functions.2
Biodegradability and other plastic properties strongly depend on the polymer structure. By changing the structure, these properties can be altered. The amount of time that a biopolymer degrades varies from only a few week to a number of months, which is mainly due to its structure.4
2. An increased need fore Biopolymers
The use of common biopolymers such as Cotton, Rayon, cellophane (all cellulose), wool and silk have been declining due to the increased use of non-renewable, petroleum based polymers such as polyester and nylon.5
These petroleum-based products are economic to produce, however are bad for the environment because they are not biodegradable. This means the environement cannot naturally decompose them. The discarding of plastic bags, plastic bottles and nylon fabric causes major pollution problems, which can damage bird and marine life and are an eyesore in landscapes. This is because they take decades and decades to degrade, some of which do not degrade.
In Australia, the development of a bio-plastics industry has the potential to benefit the environment and agriculture in Australian by creating new markets for crops and greater competition for farmers.3
As we enter a new age of high priorities for renewable energy and management of waste, there is a major interest in biopolymers and the efficiency with which they can be produced. Processing and plant breeding technologies are becoming very economic and improving material properties, as well as narrowing the cost differential between synthetic plastics and bio-plastics.3
3. PHA’s
a) Background information
PHAs (Polyhydroxyalkanoates) are linear produced in nature by of or . More than 100 different can be combined within this family to give materials with extremely different properties.6
They can be either or materials, with ranging from 40 to 180°C. The most common type of PHA is (poly-beta-hydroxybutyrate). PHB has properties similar to those of PP, however it is stiffer and more brittle.6
PHBs (Polyhydroxybutyrate) are derived from PHAs and there structure is:
O – CH – CH2 – CO – O – CH – CH2 – CO – O – CH – CH2 – CO – O – CH –
CH3 CH3 CH3 CH3
b) Recent developments
The productions of PHAs have been increased by researches on large scale production to produce biodegradable plastics which can be globally commercialised. Production costs of PHAs are to expensive compared to the cost to produce synthetic plastics. This is because the bacterial fermentation isn't economically feasible. This is why scientists have redirected their research to . Plants have the ability to produce high quality commercial products in large amounts at a low cost, making them attractive candidates for PHB production.8
c) Evaluation of properties and uses
The biodegradability of PHBs is 100%, which means it is environmentally friendly. PHB is degraded to carbon dioxide and water by fungi and bacteria through its secreting enzymes. The poor physical properties of PHB e.g. stiff, brittle and hard to process make it unfavourable for commercial use. PHAs will require further research before its commercial production will replace synthetic plastics.7
Bibliography
1.
2.
3.
4.
5. R.Smith, Conquering Chemistry, Fourth Edition
6.
7.
8.