"The world will not get out of the present state of crisis if it does not change the way of thinking that generated it." (Albert Einstein)
The many fields of plastics application, should not underestimate the problems related to the strong environmental impact that comes from their production and later disposal. Traditional plastic objects, in fact, in addition to being made using non-renewable resources, are reabsorbed by the environment only after long periods of time: a plastic bottle takes - for example - more than 400 years to decompose.
This context has stimulated the demand for eco-sustainable and biodegradable products with low environmental impact such as bioplastics, considered the green alternative to black gold, coming from natural and renewable sources.
Gianeco S.r.l. plays an important role in the recovery and recycling of post-production waste of bioplastics, providing a primary service for companies producing eco-sustainable products throughout Europe, which have a growing need to find a solution for the recovery of waste of these innovative materials.
Biodegradable plastics can represent a valid solution to the problems of post-consumer disposal, which is more and more expensive both in economic and environmental terms. However, the enormous benefits of using bioplastics are unfortunately not enough for their large-scale use. First and foremost,there is the economic factor: market conditions are needed to discourage the production of traditional plastics, which are still much cheaper. Moreover, bioplastics do not always offer the same quality guarantees as traditional ones. There is a constant need for investment and greater attention to research: in fact, high costs for developing new technologies undermine the economic competitiveness of bioplastics. What bodes well for the large-scale introduction of these new materials is the growing awareness of environmental issues, which could represent a decisive stimulus towards the promoting of legislative initiatives in favour of research.
Polymers from renewable sources are divided into:
Starch polymers
Polylactic Acid (PLA)
Polyhydroxyalkanoates (PHA, PHB)
Cellulosic polymers
Starch polymers are the most common biopolymers on the market today, also because of their relatively low cost. They are polymers obtained from natural starch by chemical, thermal and mechanical treatments. Starch is currently obtained from maize, wheat, potatoes, tapioca and rice. The mechanical characteristics of starch polymers are, in general, lower than those of polymers from petrochemical sources. Starch polymers are quite easy to process, but are sensitive to thermal degradation and tend to absorb moisture. Starch is a thermoplastic material, it can be softened if heated, moulded and extruded, and can therefore be processed with the classic techniques of the plastics industry. A major disadvantage is that its physical properties, which are highly dependent on moisture, make it unsuitable for many applications. The method used to develop practical applications for starch-based polymers is to combine it with another compatible and biodegradable polymer (of petrochemical or natural origin) to improve its properties. An example is Mater-Bi which is a hybrid in the sense that it consists of both a renewable and natural component (starch) and a non-renewable and synthetic petroleum-based (PCL).
Since 2002, PLA has been being the second biopolymer, marketed and sold on a large scale. This material has excellent physical and mechanical properties, making it the best candidate to replace thermoplastic polymers from petrochemical sources (for some applications). The high price has long limited the use of this material to niche or medical applications, while recent innovations in lactic acid fermentation technology have opened up possibilities to produce large volume of PLA. It is important to note that this material needs biodegradation to be started through hydrolysis under certain industrial composting conditions (optimal composting conditions of 65°C and 95% humidity). PLA is produced through the extraction of starch from biomass, transformation of starch into sugar by enzymatic or acid hydrolysis. The sugar is fermented by bacteria. Later, there are two ways to follow to convert lactic acid into a high molecular weight polymer: the first one through lactic acid (the product obtained is polylactide), the second one is direct polymerization through a polycondensation process and production of polylactic acid.
PLA can be compared mainly to PET-A and can be converted on the same production lines (blow-moulding, injection-moulding, extrusion and thermoforming). Higher flow rates grades are also available, which can be easily used in injection moulding applications where PLA can be a valid substitute for polystyrene (PS). This biopolymer is also very suitable for fibre extrusion, as it can validly replace polypropylene (PP). PLA has good mechanical properties compared to standard thermoplastic materials. It has low impact resistance, comparable to non-plasticised PVC. PLA's hardness, stiffness, impact strength and elasticity, important for applications such as beverage containers, are similar to those of PET. PLA oriented film can be folded, has good resistance to torsion, typical properties of paper and aluminium foil, not common in plastic films. These properties, the high flexural modulus and high transparency, make PLA film a material comparable to cellophane film. Today 70% of PLA, as well as starch, is used in the packaging of bread, milk, juices, water, perfumes, detergents, fats and oils. However, polylactic acid is not suitable to contain hot liquids due to its low softening temperature.
Typical applications of PLA (polylactic acid) are:
thermoforming: containers, trays for sweets, glasses, cups and coffee capsules;
blow-moulding: water bottles (without gas), fresh juices and cosmetic bottles;
finally, the versatility of this material is also very interesting for all 3D printing projects.
Its use in other fields is still being tested. This bioplastic is still too expensive in the case of the agricultural application or not yet enough performing for building industry. PLA is used for some automotive interior parts, in computer industry, medicine. PHA and PHB polyhydroxyalkanoates are high quality, renewable polyesters that can be used in a variety of applications, but are unfortunately sold in small quantities on the market due to high production costs. PHB has good thermal properties (melting point 180°C) and can be processed like classic thermoplastics. It can be used for both low and high temperature applications, from -30°C to +120°C. Perishable goods can be packaged in PHB wrappers and treated by steam sterilization. PHB products can be sterilized in an autoclave. However, PHB is quite rigid and brittle, which limits its applications. PHB is water insoluble and quite resistant to hydrolytic degradation. This differentiates it from most of the other currently available bioplastics, which are very sensitive to moisture and water-soluble. PHB has excellent resistance to solvents, greases and oils, good UV resistance, but low resistance to acids and bases. PHB is free of catalysts traces and is toxicologically safe. The monomer and the polymer are natural components and metabolites of human cells; thanks to this characteristic PHB can be used for products that come into contact with skin or food. PHA is completely biodegradable under both anaerobic and aerobic conditions. Without composting conditions they remain "intact" for years.
Cellulosic polymers were born in the second half of the nineteenth century and today their market has narrowed down to niche applications. In fact, following the introduction of synthetic polymer films in the 50s (due to their easy processability, high durability and good mechanical properties), cellulosic polymer films have lost their importance in the market. Cellulosic polymers, with their relatively high price compared to petrochemical polymers, have been relegated to niche applications or relatively low volumes.
Other biodegradable polyesters can potentially be produced from fossil sources: PTT, PBT, PBS, PBAT, PCL. PBS is a biodegradable synthetic aliphatic polyester with properties similar to PET; it has acceptable mechanical properties and can be used in various applications through traditional transformation processes. Main applications include mulch films, packaging films, bags and handbags, disposable hygiene products. PBS is generally mixed with other materials, such as thermoplastic starch or adipate copolymers (PBSA) to make its use more economical.
PBAT: The most important aliphatic-aromatic copolyester is the Ecoflex produced by Basf, a copolymer of terephthalic acid, adipic acid and 1-4 butanediol. The material is sold pure and can then be mixed with other biodegradable polymers (such as starch products), mainly for the production of agricultural films. Its compatibility with PLA, other polyesters and starch products is excellent (according to Basf technical data sheet). According to the company, it is also possible to reduce the film thickness to 10 μ. Its characteristics are similar to those of LDPE and it is transformed on the conventional lines. Films made from Ecoflex are used for compost bags, mulching films, coating or lamination of paper when high moisture resistance and grease resistance are required, oriented films.
