Biopolymers - Thermoplastic polymers, elastomers and additives

The polyhydroxyalkanoates (PHA) comprise a group of natural biodegradable polyesters which are synthesized by microorganisms even through the bacterial fermentation of lipids or sugar. However, several disadvantages limit their competition with traditional synthetic plastics or their application as ideal biomaterials. These disadvantages include their poor mechanical properties, high production cost, limited functionalities, incompatibility with conventional thermal processing techniques and susceptibility to thermal degradation. To avoid these drawbacks, PHAs must be modified to ensure improved performance in specific applications. In this review, the well-established modification methods of the PHAs are summarized and discussed. The improved properties of PHA which is combined with natural raw materials or other biodegradable polymers are summarized, including starch, cellulose derivatives, lignin, poly (lactic acid), polycaprolactone and different mixtures of PHA type. The functionalization of PHA by chemical modification is described with respect to two important synthesis approaches: block copolymerization and graft copolymerization. It also addresses the expanded use of modified PHAs as engineering materials and the biomedical importance in different areas.

PBAT is a biodegradable synthetic aromatic aliphatic copolyester, derived mainly from 1,4-butanediol, adipic acid and terephthalic acid. Its chemical structure is formed by an aliphatic part that is responsible for its biodegradability, and an aromatic part that provides good mechanical properties. PBAT is a synthetic copolymer with good mechanical properties. This polymer is biodegradable, since it degrades completely, in a short space of time, by microbial attack (fungi, bacteria and enzymes) under appropriate conditions in the environment. However, these materials present the same problem: they degrade significantly during processing, compromising their mechanical properties and, consequently, their applications. Therefore, additives are used to prevent early degradation of these polymers, as processing aids (plasticizers and lubricants), thermal and UV stabilizers, mineral and vegetable fillers, nanofillers, curing and grafting agents, etc. Thermoplastic amorphous thermoplastic, compostable and biodegradable biodegradable compostable, very flexible, similar LDPE - LLDPE, good thermal stability, up to 230ºC, low water barrier properties, good processability in film extrusion by blowing. Applications in films for food packaging and agriculture

It is the acronym with which the Crystallized PLA is indicated. Crystallization is a process that converts PLA (originally amorphous) capable of resisting higher temperatures, up to 85 ° C. Exactly like the PLA biopolymer from which it is derived, it is biodegradable and compostable according to EN13432. Once crystallized, the CPLA loses its original transparency and takes a milk white color. It is mainly used for the production of cup lids for hot drinks.

It is obtained from the bagasse of fast growing plants, especially sugar cane, bamboo or straw and, consequently, it is constituted by natural materials, as well as being totally biodegradable and compostable according to EN13432. The pulp is white and resists up to a maximum temperature of 100 ° C. Suitable for microwave and traditional oven. It is mainly used for the production of plates and containers with lid but it is also used for some types of glasses.

Starch, anhydroglucosidic polymer, is used considerably as a biodegradable packaging material, due to its abundance and low cost. The starch is composed of two isomers, amylose (linear structure) and amylopectin (highly branched structure), whose proportion depends on the source of origin. As a bioplastic, thermoplastic starch (TPS) can be processed using plasticizers and converted into plastic. Its hydrophilic nature makes the TPS susceptible to moisture attack and causes significant changes in dimensional stability and mechanical properties. Currently there are different varieties of TPS, which combine polyesters with native starches of various origins, such as corn, potato or pea and which have different properties. This variation makes the TPS stand out for its versatility in its properties, to be easily modified with surface additives, in addition to having good properties of sealability and printability without surface treatment. The thermoplastic starch (TPS) is a polymer of low mechanical strength, obtained by the hot extrusion of starch, glycerol and water. Both materials degrade significantly during their processing, compromising their mechanical properties and, consequently, their applications.

Polycaprolactone (PCL) is an aliphatic polyester, degradable in the environment such as rivers, lake waters, sewer effluents, soil and compound. The properties of polymer blends depend very much on the morphology resulting from the interaction between their components. Thus, the selection of the components of the mixtures constitute an extremely important task to obtain a quality product. Blenda of PCL with natural polymers, such as proteins, celluloses and carbohydrates, have been particularly interesting. They consist of two distinct phases, whose interface is weakly linked with poor interaction due to the apolar characteristic of the PCL and polar of the natural polymers and many proteins, resulting in low physical properties. A third component (compatibilizer) is added to increase the compatibility of an immiscible mixture, improving the interfacial adhesion of the mixture and therefore its mechanical properties. In 1977, PCL and maleic anhydride were used as compatibilizers (PCLMA). The PCL is a plastic material with high flexibility. Stretching and breaking stress of PCL films have higher values ​​than a similar, but non-biodegradable material, such as low density polyethylene. However, since PCL has a low melting point (approximately 65 ° C), it is difficult to process it by conventional techniques for thermoplastic materials. However, such processing difficulties can be improved with mixtures of PCL and types of carbohydrates; such as: starch, wheat, soybeans and sago, reducing costs and increasing the biodegradability of the materials obtained. Semi-crystalline thermoplastic with low viscosity, flexible, similar LDPE. Low thermal resistance, low processability due to low viscosity (T ª extrusion 70-80 ºC), high permeability to water, oxygen and CO2, low biodegradation speed (2 years). Applications in films and coatings. Mixtures with other biodegradable to improve properties.