The goal of this post is to present the different types of polymers labeled as “bioplastics”, and their environmental impact.
The subject has been too complex for me to deal in one post, So in this first part I’ll try to clarify the main definitions for materials and processes normally associated with the terms “bioplastics” or “biopolymers “. In a second post I’ll analyze the pros and cons of the main two different types of bioplastics according to their biodegradation mechanism.
Plastic materials are ubiquitous. They are light, flexible, durable have good chemical resistance and are relatively affordable.
However, they present several environmental problems: they depend on oil reserves, contribute to CO2 emissions and their durability and ubiquity makes them a problematic residue.
Currently plastic waste management options are landfill, incineration and recycling/composting (with a previous collection and sorting step). Each of these options comes with its own environmental side-effects (difficulties in sorting, energy expenditure, toxic emissions).
The conspicuity of plastic in the environment and increasing public sensitivity have made this search for plastics with reduced environmental impact evolve into the creation of the so call “bioplastics”.
Packaging is the “poster child “industry of plastic waste, producing large numbers of disposable plastic articles.
Biopolymers, Biodegradeble plastics, Bioplastics…
Plastics are carbon-based polymers (long-chain molecules that repeat their structures over and over) mostly made from petroleum.
The term bioplastic or biopolymer can be used to characterize two types of polymeric materials:
- Those obtained from a renewable source.
- Plastic materials that are completely biodegradable and compostable (according to EN 13432 in Europe ASTM D 6400  and ASTM D 6868  in the US, while. Australia and New Zealand refer to the AS 4736  standard).
However, the lines between bioplastics and biodegradable and compostable plastics may blur because of the different combinations and mixtures between these different materials.
Degradation of a polymer is any physical or chemical change caused by environmental factors, such as light (photodegradation), heat (thermodegradation or oxidative degradation), humidity (hydrolytic degradation) that induces changes in the polymer properties that result in “cuts” of the polymeric chain.
So, what does biodegradable mean?
Biodegradable polymers (let’s call them BDPs) are those that experiment degradation reactions under the action of microorganisms such as fungi or algae under natural conditions occurring in the biosphere and during a short period. CO2, H20 and new biomass result from these reactions in presence of oxygen, and CO2, CH4 (methane) and new biomass, in absence of oxygen (ASTM 6400-99).
A subset of BDPs may also be compostable with specific reference to their biodegradation in a compost system. Here’s an interesting presentation about compostable polymers.
Industrial composting conditions involve (relatively) high temperature (55-60°C), high relative humidity and the presence of oxygen,. According to the EN13432 standard, plastic packaging can only be called compostable if it is demonstrated that:
- The packaging material and its relevant organic components (>1% weight) are naturally biodegradable.
- Disintegration of the packaging material takes place in a composting process for organic waste within a certain time.
- The packaging material has no negative effect on the composting process.
- The quality of the compost is not negatively influenced by the packaging material.
Home composting involve milder conditions (mainly lower temperature), since there is a much smaller amount of compostable material.
Vinçotte is a Belgian accredited inspection and certification organisation has its own test standard for the certification of home compostable materials. An EN standard is currently being developed (De Wilde et al., 2016)
So we after reviewing what is a biopolymer and what is degradable and compostable, let’s check the different types of Bioplastics.
Types of Bioplastics
According to the first part of the definition in Section 2, that is to say, polymers obtained from a renewable source, let’s call them bio- based, and can be classified in:
Polymers obtained directly from natural sources. These are natural polymers easily available, extracted from animals or plants. Some examples are polysaccharides (starch, cellulose) and proteins (casein, gluten).
Polymers obtained by chemical synthesis from renewable biological monomers. The best example is PLA , polylactic acid obtained from monomers existing in lactic acid.
Polymers obtained form micoorganisms or genetically modified bacteria: Mainly Polyhydroxyalkanoates PHAs.
According to the second part of the definition (biodegradable polymers) we can differentiate:
- Biodegradable bioplastics: starch based, PLA, PHAs (more later).
- Biodegradable fossil-based polymers: The main example is polycaprolactone, degraded by the action of different types of bacteria (more here)
And finally, we should talk about this type of non bio-based polymers:
- Polymers degradable thanks to the incorporation of additives (organic or oxo type)
There are several reasons for mixing different biodegradable polymers: reduce manufacturing costs, increase efficiency, adapt the degradation speed to the existing ambient conditions, achieve different combinations of the properties form the different materials- Synthetic biodegradable polymers tend to complement each other’s properties ,as well as those of PLA starch and the organic materials.
A couple of graphics to summarize all this:
Source: European Bioplastics
This is all for now, come back in June for the second part of the post.
May 2018, Bruno Rey- The Packaging Blog-