1. Introduction
We can classify the polymers alone by many criteria – listed below are some of them.
Classification by physicochemical properties:
Thermoplasts – materials that become soft when heated, and become hard after a decrease of temperature. E.g. acrylonitrile-butadiene-styrene – ABS, polycarbonate – PC, polyethylene – PE, polyethylene terephthalate – PET, polyvinyl chloride – PVC, poly (methyl methacrylate) – PMMA, polypropylene – PP, polystyrene – PS, extruded polystyrene foam – EPS.
Thermoset (duroplasts) – after being formed they stay hard, they do not become soft with the influence of temperature. E.g. polyepoxide – EP, phenol formaldehyde resins – PF.
Elastomers – materials, which can be stretched and squeezed and are able to reshape back to their original form when the
applied stretching and squeezing force is removed.
Classification by origin:
n Synthetic polymers – originate from chemical synthesis (addition polymerization1, polycondensation2, copolymerization3).
n Natural polymers – produced and degraded in nature e.g. cellulose, proteins, nucleic acids.
n Modified natural polymers – those are natural polymers, chemically changed to receive new functional properties e.g. cellulose acetate, modified protein, modified starch.
Classification by origin of raw materials, which polymers are made of:
n Renewable sources (plant and animal sources).
n Non-renewable/Fossil sources (oil, natural gas, coal).
Classification by usage of polymers:
n Packaging.
n Building and Construction.
n Automotive.
n Electrical and electronic applications.
n Medical.
Classification by susceptibility to microorganism / enzymatic attack:
n Biodegradable (polylactide – PLA, polyhydroxyalkanoates – PHA, regenerated cellulose, starch, linear polyesters).
n Non-biodegradable (polyethylene – PE, polypropylene – PP, polystyrene – PS).
There are, of course, many more types of classifications of polymers available, however it is important to know that in industrial applications polymers alone are often not enough. Most plastics contain other organic or inorganic compounds blended in. Those are called additives and they can provide new properties to plastics.
Therefore: Plastics = Polymer + Additives
The amount of additives ranges from very small percentages for polymers used to wrap foods to more than 50% for certain applications. Such polymers with additives in technical and industrial usage are called plastics.
Some examples of additives include: plasticizers oily compounds that confer improved rheology, fillers that improve overall performance and reduce production costs, stabilizers that inhibit certain chemical reactions such as fire retardants – additives decreasing flammability, antistatic agents, colouring agents, sliding agents and many more.
The world of plastics is immense, given the broad range of different polymers and additives that can be compounded. This in turn gives a wide range of possibilities to transform and process plastics. Most basic techniques in plastics processing are: extrusion, blow extrusion, injection, compaction/compression, pressing, board/slab forming, rolling and calendaring, and die-casting.
2. History of plastics and shift towards sustainability
First plastics were produced in the end of 19th and beginning of 20th century. Celluloid and cellophane were first ones and they were natural source based – biobased. After 2nd World War plastics became very popular. From ’60 till ’90 they have mainly been produced from petrochemical resources. In ’80 plastics production was larger than steel production.
In ’90 environment protection policies and the notion of sustainability became more important on both sociocultural and political scale. New technologies were invented and put into practice such as producing plastics based on renewable resources and production of biodegradable materials.
Research of new materials and their production technologies was and still is closely linked to:
n Knowledge development in environment protection issues –especially with regards to the life cycle thinking of a system – i.e. looking at production, usage and end-of-life processes, material inputs and outputs (the so called – emissions).
n Improving evaluation methods of plastics influence on environment, especially through the use of LCA – Life Cycle Assessment – a tool that takes a cradle to grave approach on a particular product.
n Development of sustainable development policies, which in manufacturing and trading practice mean that environmental, social and economic issues linked to plastics are taken
into account.
Plastics produced with such new technologies and issues in mind are collectively called bioplastics. This term was coined by the European Bioplastics Association and their definition can be seen in a box.
To illustrate this distinction European Bioplastics has provided a simple two-axis model that encompasses all plastic types and possible combinations. It can be seen on fig. 1.
As can be seen, plastics have been divided into four characteristics groups. The horizontal axis shows the biodegradability of plastic, whereas the vertical axis shows whether the material is derived from petrochemical raw materials or renewable materials. This gives possibility for four groups:
1. Plastics which are not biodegradable and are made from petrochemical resources – this category encompasses what is known as classical or traditional plastics (although classical petrochemical plastics represent only one group of plastics, they make up in total more than 90% of plastics production worldwide).
2. Biodegradable plastics from renewable resources – plastics which are made from biomass feedstock material and show the property of biodegradation.
3. Biodegradable plastics from fossil resources – plastics which can biodegrade but are produced from fossil resources.
4. Non-biodegradable plastics from renewable resources – plastics produced from biomass but without the biodegradation property.
This guide will discuss all four categories in turn.
3. Classical petrochemical plastics
Classical plastics produced from fossil resources find use in multitude areas of life. Primary property of products made from plastics is their light weight in comparison to other materials. That is because plastics have relatively low density. Moreover plastics show excellent thermo-insulating and electro-insulating properties. Plastics are also resistant to corrosion. Many plastics are transparent, and can therefore have many uses in optical devices.
Plastics can be formed in different shapes, and they can be mixed with other materials. Furthermore their properties can be easily altered and tailored by adding: strengthening fillers, pigments, foaming agents and plasticizers.
Due to plastics universality, they are used in almost every area of life. Most widespread uses include packaging, constructions, transport, electric and electronic industry, agriculture, medicine and sport. The fact that their usage possibilities are virtually unlimited and that their properties could be adapted to any requirements, is an easy answer to a question as to why plastics are the source of innovations in all life areas.
All this is possible thanks to many different types of plastics available on the market.
The big six plastics in the market are:
n Polyethylene (PE).
n Polypropylene (PP).
n Polyvinyl chloride (PVC).
n Polystyrene (solid – PS and expanded/foamed – EPS).
n Polyethylene terephthalate (PET).
n Polyurethane (PUR).
Combined they make up about 80% of demand for plastics in Europe. Top three plastic groups in market are: polyethylene (29%), polypropylene (19%) and polyvinyl chloride (12%). (Source: Plastics Europe – The Facts 2012, [1]) as can be seen from fig. 2.
Other types of plastics with significant demand include:
n Acrylonitrile butadiene styrene (ABS).
n Polycarbonate (PC).
n Polymethyl methacrylate (PMMA).
n Epoxide resins (EP).
n Phenolformaldehyde resins (PF).
n Polytetrafluoroethylene (PTFE).
In 2011 global production of plastics has reached 280 million tons. Production is experiencing a steady increase average of about 9% per year from 1950s. In 2011 plastics production in Europe reached 58 million tons (which in turn makes up a 21% of global production). The biggest worldwide producer (China) reached 23% of global production. In the long term, it is forecasted that 4% growth of consumption per capita is going to take effect. Despite high consumption in Asia and by the new members of EU, the level of consumption in these countries is still much lower than in well developed countries [1].
Fig. 3.-6. compare progress of plastics production. Fig. 3 shows plastics growth rate since 1950 to 2011 on the world and in Europe. Plastic industry has been growing continuously for 50 years. Global production has grown from 1,7 million tons in 1950 to 280 million tons in 2011, while in Europe from 0,35 million tons to 58 million tons. Currently one can observe that the plastic production is rapidly shifting to Asia.
Fig. 4. shows demand of plastic in European countries, with the highest level in Germany, Italy and France.
Fig. 5. shows plastic consumption in Europe in 2010–2011. Consumption has risen from 46,4 million tons in 2010 to 47 million tons in 2011. In 2010 the biggest branch was packaging with 39% in all consumption, followed by: constructions (20,6%), automotive (7,5%), electrical and electronic (5,6%). Other smaller branches are: sport, recreation, agriculture and machine production. In 2011 the biggest branch was also packaging (39,4%), a slight increase from the year before. Second biggest branch in 2011 was constructions (20,5%), automotive (8,3%), followed by electric and electrical industry (5,4%). Other smaller branches were: sport, health and safety, entertainment and relaxation, agriculture, machines industry, households appliances and furniture industry.
Fig. 6. shows plastic consumption with specified polymer type and branch.
Additional information about the classical plastics industry can be found on the website of Plastics Europe Association: http://www.plasticseurope.org/plastics-industry/market-and-economics.aspx
4. Biodegradable plastics
When searching for a definition of biodegradable plastics one can find few contradictory definitions. The easiest and the most accurate explanation of biodegradable plastics says that biodegradable plastics are susceptible to biodegradation. Biodegradation process is based on the fact that microorganisms available in the environment, i.e. bacteria, fungi and algae recognize biodegradable plastics as a source of nutrients and consume and digest it (artificial additives are NOT needed). Biodegradation includes different parallel or subsequent abiotic and biotic steps and MUST include the step of biological mineralization. The first step of biodegradation is fragmentation which is followed by mineralization. Mineralization is conversion of the organic carbon into the inorganic carbon. Fig. 7. describes the difference between degradation and biodegradation.
As we can see biodegradation is complete microbial assimilation of the fragmented material as a food source by the microorganisms. To be completely accurate we have to say that the term biodegradability does not give any specific answer about the process, it only says that the complete assimilation of the organic carbon occurs. If we take the infinitive timeframe everything is biodegradable. More accurate term is compostability, meaning biodegradation in the composting environment and in the timeframe of a composting cycle.
As we said before biodegradation can occur in an aerobic or in an anaerobic environment. Products of the biodegradation under aerobic conditions are carbon dioxide, water and biomass and the products of anaerobic biodegradation are methane, water and biomass, which is simplified described in the fig. 8.
Among the different biodegradation processes, composting is an organic recycling procedure, a manner of controlled organic waste treatment carried out under aerobic conditions (presence of oxygen) where the organic material is converted by naturally occurring microorganisms. Compostability is complete assimilation of biodegradable plastics within 180 days in a composting environment. During industrial composting the temperature in the composting heap can reach temperatures up to 70°C. Composting is done in moist conditions. Compostable plastics are defined by a series of national and international standards e. g. EN 13432, ASTM D6400 and other.
The susceptibility of a polymer or a plastic material to biodegradation depends exclusively on the chemical structure of the polymer. For this reason, whether the polymer is made of renewable resources (biomass) or non-renewable (fossil) resources is irrelevant to biodegradability. What matters is the final structure. Biodegradable polymers can therefore be made of renewable or non-renewable resources.
4.1. Biodegradable plastics from renewable resources
Knowledge development in environmental protection, sustainability and depletion of world fossil resources influenced scientists to find alternative energy sources. One of the trends involved research of biodegradable polymers from renewable resources. Those plastics could replace ordinary petrochemical plastics, and have similar properties.
First small manufacture production of biodegradable plastics from renewable resources started in 1995. Nowadays its usage and range of adaptations is much wider. In 2009 global biodegradable plastics production amounted to 226 thousand tons. In 2011 it reached for about 486 thousand tons [2] (doubling of the production in two years).
Main types of biodegradable polymers produced from renewable resources (including those produced by chemical synthesis of bio-based monomers and those made by microorganisms or modified bacteria) are the following:
n Poly(lactic acid) (PLA).
n Thermoplastic starch (TPS), starch mixed with aliphatic polyesters and co-polyesters; starch esters, starch mixed with natural materials.
n Polyesters with microbiological origin – poly (hydroxyalkanoates); PHAs, including copolymers of butyric acid, valeric acid and
hexanoic acid PHBV, PHBH.
n Cellulose esters, regenerated cellulose.
n Wood and other natural materials.
There are many different biodegradable plastics on the market. Those which deserve most attention are: polylactides – PLAs, polymer-starch composites, polyhydroxyalkanoates (PHAs) and new generation cellulose films. They have good overall properties comparable with traditional plastics, their production capabilities are increasing substantially and prices are comparable to the prices of conventional plastics. Fig. 9. shows examples of biodegradable plastics.
Polylactic Acid – PLA
PLA – polylactide – aliphatic polyester produced by poly-condensation of lactic acid (produced from corn starch by bacterial fermentation method). PLA can be used to produce [3]:
n Flexible packaging (biaxial oriented films, multilayer films with sealable layer).
n Extruded durable and thermoformed film.
n Injection moulded packaging.
n Laminated paper extrusion.
Polymer-starch compositions
A significant progress is also observed in the field of polymer-starch composition. Those compositions are used for thermoformed flexible and durable films. They are used for trays, containers, foamed fillers in transport packaging, durable packaging formed by injection moulding, and coating of paper and cardboard.
Polyhydroxyalkanoates (PHA)
PHAs are a large family of copolymers with properties ranging from hard solids to soft materials, depending on composition. PHAs can be blended with other biodegradable polymers to form biodegradable blends. PHAs can be processed into blown films, calendered sheets, injection molded items, they can be foamed and used for paper coating.
New generation of cellulose films
New generation of compostable cellulose films are also becoming more and more widespread. Most important properties of these materials are:
n Excellent optic properties.
n High barrier for oxygen and aromas.
n Adjustable barrier for water vapour.
n Thermo-resistance, fat-resistance, chemical-resistance.
n Natural antistatic properties.
4.2. Biodegradable plastics from fossil resources
With regards to the origin of building blocks of biodegradable plastics one can distinguish two major groups:
n Polymers produced from renewable resources – those were described above.
n Polyesters made from fossil resources.
The difference between those materials lies only in the origin of the feedstock material. As they are both biodegradable, it may be possible to compost them – offering an alternative end-of-life option.
However it is important to note that the origin classification is just theoretical because many producers use polymers mixtures – i. e. mixtures of biodegradable polymers which originate from both renewable and fossil resources.
Examples of biodegradable polymers originating from fossil resources are the following:
n Synthetic aliphatic polyesters – polycaprolactone (PCL), polybutylene succinate (PBS).
n Synthetic aliphatic-aromatic copolymers such as polyethylene terephthalate/succinate (PETS).
n Poly (vinyl alcohol) (PVOH) a biodegradable water-soluble polymer.
4.3. Oxo-degradable plastics
One of the materials very often being aggressively promoted as biodegradable are oxo-degradable plastics. Those materials are available on the market and often improperly labelled as environment friendly biodegradable materials.
To produce oxo-degradable plastics the producers add specific degradable additives to the conventional non-biodegradable plastics. Those materials then fragment into small pieces and become undetectable in the environment with the naked eye. But this only proves the first step of degradation, the second necessary step for materials being called biodegradable, MINERALIZATION, is not proven. More information on the oxo-degradable plastics ban be found on the following webpages:
n The Society of the Plastics Industry, Bioplastics Council – Position paper on degradable additives (http://goo.gl/MoqGJ).
n European Bioplastics – Position paper on British standard for oxo-degradable plastics (http://goo.gl/GJXJO).
n European Bioplastics – Position
paper on Oxo degradable plastics (http://goo.gl/RvPgi).
n European Bioplastics – Position paper European Bioplastice on the study Life Cycle assessment of oxo-biodegradable, compostable and conventional bags (http://goo.gl/tpwyN).
4.4. Plastics from renewable resources
So far the guide has listed bioplastics which demonstrate the property of biodegradation. The second group of bioplastics which gains more and more popularity and publicity are non-biodegradable plastic materials which are produced by using renewable feedstock material, as opposed to the fossil fuels. Those materials are identical in their properties with traditional plastic materials from fossil resources.
Great example of such bioplastics is the so called green polyethylene – where ethylene is polymerized from ethanol, which is produced by fermentation of organic material. There are several varieties of „green” ethylene being produced – of both high and low density (HDPE, LDPE). Fig. 10. shows the manufacturing process utilised.
Another example of renewable resources usage are PET bottles – called Plant Bottle. Those bottles are composed of PET, produced from terephthalic acid (70% of mass) and ethylene glycol (30% of mass). Terephthalic acid comes from oil, whereas glycol is produced from ethanol (deriving from fermentation of vegetable feedstock). Such bottles can be easily recycled, and they can be collected with other (classical) PET bottles. This partially bio-based PET saves global fossil resources and also reduces CO2 emissions. Plant Bottle is 20% biobased (20% of the carbon present in the material comes from renewable resources) and 30% bio-massed (30% of the mass of the material comes from renewable resources) and a simple scheme on figure 11. shows how the Plant Bottle is made.
Currently developments are made to introduce 100% biomass [6] PET bottle. 100% Bio-PET bottles will be made of organic materials such as: grass, bark and corn which are not used in food producing processes. In future also agricultural by-products (like potato peelings) and other bio-waste will be used. To make 100% biomass bottle it is necessary to produce terephthalic acid from renewable resources. There are some chemical pathways to produce terephthalic acid from p-xylene but at the moment no 100% PET is jet present at the market.
Alternative to such fully bio-based PET, very much interest is currently addressed to polyethylenefuranoate (PEF), a polyester totally bio-based for the same applications as PET but with even better properties for food packaging.
Furthermore as a consequence of fast technological progress some petrochemical polymers in the near future could be manufactured from renewable resources.
5. Bioplastics manufacturing capabilities
In 2011 global bioplastics producing ability amounted to about 1,161 million tons. It is much less than global classic plastics production (265 million tons) but forecast for 2016 shows that bioplastics production will reach almost 6 million tons per year. Fig. 12. shows these data with biodegradable and non-biodegradable plastics separately.
Fig. 13. on the other hand presents bioplastics production capability in 2011 and forecast for 2016 for different regions. In 2011 the biggest production ability was in Asia (34,6%), South America (32,8%), Europe (18,5%) and North America (13,7%). In 2016 forecast shows that the largest production will occur in both Asia (46,3%) and South America (45,1%), followed by Europe (4,9%) and North America (3,5%).
Fig. 14. presents bioplastics production capacity by type and fig. 15. shows the same forecast for 2016. The most crucial and noticeable difference lies in the prediction of BIO-PET usage.
European Bioplastics has predicted (fig. 16.) that in 2016 more than 80% of bioplastics market share by type will be taken by the production BIO-PET. This prediction is based on the press releases of several industry leaders in beverage production, stating their intention to exchange traditional PET bottles into their bioplastic equivalent (BIO-PET and PEF).
References
[1] PLASTICS EUROPE – The Facts 2012:
http://www.plasticseurope.org/cust/documentrequest.aspx?DocID=54693
[2] European Bioplastics: http://en.european-bioplastics.org/
[3] Widdecke H, Otten A., Bio-Plastics Processing Parameter and Technical Characterisation. A Worldwide Overview, IFR, 2006/2007.
[4] Morschbacker A., Biobased PE – A Renewable Plastic Family, Braskem S. A., European Bioplastics Conference Handbook, 21-22, Paris, November 2007.
[5] Cees van Dongen, Dvorak R., Kosior E., Design Guide for PET Bottle Recyclability, UNESDA&EFBW, 2011.
[6] Word’s First 100% Plant-Bassed PET Bottle, „Bioplastics Magazine” No. 2/2011, p. 25.
