PHB physical properties similar to polypropylene. However, PHB is perfectly isotactic and does not include any chain branching like, for instance, PE. During processing, it flows easily. It is insoluble in water and soluble in chloroform and other chlorinated hydrocarbons. It exhibits good barrier properties against oxygen and compared to other biopolymers. It possesses better physical properties than polypropylene for food packaging applications. (Chaijamrus & Udpuay, 2008)
As a homopolymer, PHB is highly crystalline (50%-70%). It is an important characteristic of a polymer in order to regulate the mechanical properties of the material. The value of water vapor transmission rate (WVTR) of PHB is about 5.6 g/m2/24h …show more content…
Izod impact strength of PHB is 35-60Jm-1 which indicates the impact resistance. Impact resistance is the ability of a material to withstand a high force or shock applied to it over a short period of time. A high force over a short time has a greater effect than a weaker force over a longer period of time. The impact is also proportionate to the relative velocity of the colliding materials. Therefore, the impact resistance of properties of materials is important when considering the use of these materials for the safety of personnel or equipment at a risk of encountering impact. (Arcana et al., 2000)
Chemical properties of PHB:
Compare with other synthetic polymers, PHB does not contain any residues of catalysts. PHB is a completely biodegradable polyester which degrades into carbon dioxide and water under aerobic conditions. It is non-toxic and has highly biocompatible. Due to these, it having some applications in different fields as biomedical and environments. PHB relatively resistant to hydrolytic degradation but poor resistance to acids and bases.
Thermal properties of …show more content…
If process parameters vary too widely, PHB’s relatively small difference between melting and decomposition temperature. The small difference between these two temperatures can be attributed to the high melt temperature due to strong intermolecular interaction.
3. Another problem for PHB is the progressive decrease of its mechanical properties, such as tensile strength, because of secondary crystallization and gradual loos of plasticizers over time.
The secondary crystallization that occurs during storage at room temperature forms new lamellae in the amorphous phase. It has a low nucleation density. Therefore, it forms large spherulites with cracks and splits, which have a negative influence on the mechanical properties.
Many references to attempts to mix PHB with other polymers, in order to achieve the aim of increasing mechanical properties of PHB. Unfortunately with only limited success up until now. Most polymers cannot be mixed from a thermodynamic point of view. The chemical incompatibility does not permit a good mixture
4. The major commercial drawback of the bacterial PHBs is their high production cost, making them substantially more expensive than synthetic plastics. Compare with synthetic plastics, it has high enzyme costs, as well as the use of a relatively expensive substrate. (Abd-El-Haleem, et al.,