According AIMPLAS, Spain consumed 5 million tons of plastic annually, of which only manage to recycle 700,000 tonnes, the rest goes to landfill. The solution: biodegradable plastics.
Pascual Bolufer, Sarrià Chemical Institute
Let's start with the problem: it is to transform the polymer into CO2, water and some biomass. It is understood as biodegradable feature of some chemicals can be used as substrates by microorganisms (bacteria, fungi and algae), which used to produce energy and create other molecules such as amino acids, new fabrics and new organisms.
ISO (International Standard Organization) defines biodegradable plastics such as polymers that are degraded by microbial action.
Biodegradation can be used in the removal of certain pollutants, urban organic wastes, and semi-flexible plastic, paper, oil, etc.. But in landfills, which contain heavy metals or extreme pH, the plastic will not degrade. In these cases treatment is required prior to stop dumping at acceptable conditions for the bacteria, which performed its function at an acceptable speed.
The aging and degradation may be pursued by anaerobic or aerobic.
The combined action of ultraviolet radiation (photodegradable), heat and atmospheric oxygen, destroys the chemical bonds of biopolymers. Are slow processes. The polymer eventually fragment into smaller chains.
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The destruction of common materials require different periods of time: while a banana skin needs 2-10 days (depending on season), a milk carton (Tetra Pack) requires 5 years and a glass bottle takes 4,000 years. While the plastic bag disappears within 10-20 years, the soil and subsoil preserved traces of this degradation for several decades.
How they react to heat? Evil intra and intermolecular bonds, which ensure the cohesion of bioplastic, are easily broken when the temperature rises. In the amorphous plastic, low temperature, the chains will not travel far, are intertwined, and intermolecular forces involved in bringing cohesion to the system. Above a temperature called the glass transition, the chains move more freely because the intermolecular forces have disappeared. Because of this, you get a soft plastic that increases its fluidity as the temperature rises. In fact, the material behaves like a plate of spaghetti: hot slide over each other, but cold are intertwined, like a ball of wool.
The glass transition temperature varies greatly from one plastic to another. Depends primarily on the length of the strings: if you are long, the chains are intertwined and the glass transition temperature is high.
The thermosetting plastic is very different from bioplastic. Polymers are infusible and insoluble because the chains form a three-dimensional lattice space, intertwined with strong covalent bonds. The mobility of their chains and degrees of freedom for rotation on the links is practically zero. Temperature is well supported, some examples are vulcanized rubber, bakelite, silicones, etc..
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Degradable plastic.
Plastic produced by microbes
The bioplastic is a natural polymer derived from starch, cellulose, soybean oil, corn, etc.. and is produced by a living organism and biodegradable nature.
Its origins date back to 1926, when scientists at the Institut Pasteur, Paris, managed to produce polyester from the bacterium Bacillus megaterium.
In 2004, the NEC (Japan) developed a plant-based plastic polylactic acid (PLA), in turn derived from corn, or from fermentation of agricultural by-products rich in starch that have high resistance to fire. It does not require toxic chemicals such as halogens or phosphorus derivatives. The PLA is degraded by enzymes of microorganisms in the soil.
In 2005, Fujitsu introduced the manufacture of bioplastics in notebook computers and in 2006 published DVD Blu-ray format made from bioplastic.
To create a bioplastic scientists seek chemical structures that allow the material degradation by microorganisms. A well known example is the PHA (polyhydroxyalkanoate), a polymer double ecological base originated from a renewable resource and is biodegradable.
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The PHA is used to make plastic forks and films for packaging because it is resistant to heat, grease and oil.
Bioplastics can also be obtained from cellulose, vegetable oil and even milk casein.
The new generation bioplastics retain their physical and chemical properties along the life cycle of the manufactured product, but once deposited or mechanized composting conditions, will biodegrade in the same way that organic waste. The intrinsic chemical instability of these biopolymers contribute to sustainable development because they are produced from renewable resources.
The production of bioplastics is still very limited because it can not compete with the prices of petroleum-derived plastic.
Degradable plastic
Because bioplastics are high-priced, have appeared biodestructibles that are derived from petroleum, mixed with starch. Soil microbes degrade starch but is the synthetic polymer.
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Additives to degrade the synthetic polymer
Bioplastics are very environmentally friendly, but can not replace traditional polymers such broad applications as food and beverage packaging and disposables to hospitals, which is required for the property of inert plastic that ensures hygiene and avoids pollution and the spread of disease.
In the hospital disposable material can not be permitted container contamination with microorganisms, which then would go to content.
Therefore remains the use of synthetic polymer, but based degradable additives.
Worldwide there are at least two companies supplying these additives that ensure degradation: ECM Biofilms are with their ECM Masterbatch pellets (Ohio Corporation) and the British Symphony Environmental Corporate (d2w products).
When extruding polyethylene or polypropylene is added an additive, patented a colloid, which represents only 1% of plastic. The additive breaks down the carbon-carbon bonds, to lower molecular weight. In turn, diminishes the strength of plastic and other qualities.
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The additive also serves to degrade recycled resins. Part of a stabilizer additive to ensure a reasonably long life cycle for each specific application. For example, a plastic bag should have a lifespan of about 18 months before losing its strength, however, a bag of bread requires a lifetime of only a few weeks.
You can choose the life of several months to 5 years. All properties of the polymer remain unchanged during its lifetime: strength, transparency, printing and barrier.
The additive does not need a biologically active environment to start degrading the flexible plastic (landfill). It is enough to be outdoors, there is light or not, and makes the plastic in only water, carbon dioxide and a small amount of inert biomass. It does not produce methane. The bottle of mineral water or the awning of a greenhouse spray anti degrade and return to nature.
The costs are tolerable. ECM Biofilms additives required microbes, Symphony (d2w) no.
The Environment Minister can rest assured half: the plastics degrade, but mostly not come from renewable resources, but the cracking of petroleum byproducts.
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