The future viability of bioplastic production using transgenic crops: veracity, perception and marketability

Content

Introduction

1. Veracity and Reality

1.1 Background information on petroplastics and biodegradable plastics

1.2 Origin of biodegradable plastics

1.3 Biodegradability of bioplastics

1.4 Beginning of bioplastic production

1.5 The worldwide packaging problem and the composting solution

1.6 Biosafety concern by transgenic plants - necessity of growth control / physical

isolation

1.7 Future expectations on bioplastic

2. Perception and Insight

2.1 Evolution and accumulation of bioplastic in natural and recombinant bacteria

2.2 Biosynthetic pathway of bioplastic in plants

2.3 Bioplastic production in plants

2.4 Plants used for bioplastic production

2.5 Substrate sources for bioplastic production

2.6 Chemical and physical properties of petro- and biodegradable plastics

2.7 Genetic containment systems

3. Marketing

3.1 Definitions of market success

3.2 Creation of new markets by bioplastics

3.3 Market & job potential of bioplastic by means of economic value

3.4 Problems with introduction of crops into the Third World

3.5 Suitable crops for marketability

3.6 Strategy and key factors for production of cheap plastic

3.7 Limitations for bulk production of bioplastics

3.8 Production costs: plants v. bacteria

3.9 Economic competitiveness: PHA v. PVC

Conclusion

References

The future viability of bioplastic production using transgenic crops:

veracity, perception and marketability

Introduction

In the second part of the last century, plastics experienced a huge surge in demand which surpassed the total production volume of steel by far. Plastic turned into the material of industrial progress and modern consumption and displaced, to some extent, traditional materials like steel, aluminium, paper and glass.

Today’s consumers are informed about environmental problems in which waste management did not reach a corporate consensus in public yet. The public wants to see eco- friendly, recyclable or degradable materials, and the abundance of plastic waste seems to be a major problem area.

With the development of degradable plastics, a group of materials was created with regard to disposal for the first time. For economic reasons the use of degradable plastics is still negligible, but has huge potential, as these plastics are suitable for waste management to close circular flow, save oil reserves, stabilize CO 2 emission and offer consumers an environmentally friendly option.

1. Veracity and Reality

1.1 Background information on petroplastics and biodegradable plastics

Petroplastics can be divided into three categories: thermoplasts, duroplasts and high- performance plastics. Moldable thermoplasts are responsible for 70% of the worldwide plastic consumption represented by polyvinylchloride (PVC), polystyrene (PS) and polyethylene (PE). These thermoplasts demonstrate the highest substitution potential for bioplastics. Duroplasts are irreversible, non-moldable plastics, which are represented by polyurethane and epoxyresins. High-performance plastics like polyamide or polyethylene terephthalate are made of a combination of different polymers (Stöckli). A pre-requisite for modern retailing is the hydrophobic and inert character of thermoplasts. During manufacture and post-consumer

disposal, petroplastics seem to be eco-friendlier materials than biologically based polymers as they can be incinerated with heat recovery or mechanically recycled to utilize the energy content of the plastics. Petroplastics used in agricultural products have long been bioassimililated by combined peroxidation and biodegradation. Most contain transition metal prooxidants with the peroxidation products being biodegradable (Scott).

Scheme 1: Chemical structure of PHA produced in bacteria.

R-group varies from methyl (C1) to tridecyl (C13).

(Garcia, 1999)

Poly-hydroxyalcanoate (PHA) (Scheme 1), the most used representative for biodegradable plastics, is a non-toxic, biocompatible thermoplastic, produced from renewable resources. It shows a high degree of polymerisation, high crystallinity, optical-, isotactic- and piezoelectric activity and is insoluble in water. These properties make them highly competitive with non-biodegradable petroplastics (Poirier, Stöckli, Steinbüchel and Füchstenbusch). PHA synthesis from bacterial stock levelled the price to 16US$ per kilo which allowed application only in niches (Stöckli). Nowadays, production is either based directly (in plants) or indirectly (in bacteria) on photosynthetically produced precursors, at prices which are becoming competitive with those of petroplastics (Withold).

1.2 Origin of biodegradable plastics

The evolution of PHA goes back to microorganisms producing PHA under nutrient limiting conditions and an excess of carbon as storage material (visible as mobile, amorphous, lipid granules) (Barnard and Sander, Sudesh et al., Poirier). Up to now PHA was detected in over one hundred bacteria species of which Alcaligenes eutrophus and Pseudomonas oleovorans can accumulate up to 50% PHA in dry weight (Stöckli). Nature has evolved several different pathways for PHA formation, each suited to the ecological niche of the PHA-

producing microorganism (Reddy et al.). These days, depending on the carbon source and bacteria phylum, polymers with different properties are obtained for industrial use (Stöckli).

1.3 Biodegradability of bioplastics

The ASTM (American Society for Testing and Materials) standard D-5488-94d defines biodegradability as “Capable of undergoing decomposition into CO 2 , methane, water, inorganic compounds, or biomass in which the predominant mechanism is the enzymatic action of microorganisms, that can be measured by standard tests, in a specific period of time, reflecting available disposal conditions” (Demicheli). In fact, PHA is degraded upon exposure to soil, compost, or marine sediment, even at 60°C and 55% moisture level (Johnstone). An experiment by Flechter showed that 85% PHA was degraded under normal conditions in seven weeks and fully disintegrated in aquatic environment (Lake Lugano / Switzerland) within 254 days at 6°C (Flechter).

Degradation of PHA results in CO 2 and water under aerobic conditions and CO 2 and methane under anaerobic conditions, respectively (Scott). Biodegradability of PHB, an offspring of PHA, also depends on PHB depolymerase within microorganisms, exposed surface area, molecular weight, nature of monomer units, moisture, temperature and pH (Boopathy).

Scott states that PHA would not be really suitable for modern technological use as it would not be biodegradable within a realistic time scale due to antioxidants. Ideally, it should remain stable during manufacture and usage and should then start to break down rapidly after discard with conversion to biomass in an acceptable time (Scott).

1.4 Beginning of bioplastic production

The development and industrial production of PHB was initiated by Imperial Chemical Industries in 1975 in response to high oil prices. They produced and marketed Biopol ® in large amounts made by Alcaligenes eutrophus in 1982. Nowadays, R&D on PHA is focussed more on technical economical problems. Researchers are looking for cheaper energy sources (i.e. media from cheap waste products), quality enhancement and improvement in purity of PHA by synthetic enzymes (blending with other polymers to

improve their mechanical and chemical properties). Bacteria breeding is targeted to make them produce more PHA in shorter time. Lastly, the production process is reformed by an industrial transformation by means of scale effects and rationalisation in the production process (Stöckli).

1.5 The worldwide packaging problem and the composting solution

Due to the exponential growth of the human population and changes in their consumer behaviour and living conditions, an accumulation of non-degradable waste material cannot be prevented (Riesmeier et al.). With an average petroplastic production of 30 million tonnes in Europe per year, from which less than 0.1% is based on biodegradable material, rubbish already starts to affect the potential survival of many species (Margetts et al., Luengo et al.).

To solve the packaging problem composting techniques were tried to be optimised. Composting of biodegradable plastic would only considered to be a viable alternative if high quality compost is produced. Therefore, composting has evolved in the direction of an ‘in- vessel’ technique, a small reactor, shielded from its surroundings. Here, moisture, temperature, pH, aeration and retention time can be controlled and regulated (de Wilde and Boelens).

According to de Wilde and Boelens, compost can be divided into ‘Biowaste’ and ‘Biowaste Plus’. The inclusion of bioplastics into biowaste results in ‘Biowaste-Plus’. Acceptance criteria for compostable plastics is set up by biodegradation, disintegration and non-effectiveness on compost quality. Biodegradation or mineralisation is defined by the conversion of bioplastic to CO 2 , water and microbial constituents. In this way, hydro- biodegradable polymers fragmentize and mineralise and thus increase the fertilizer value of the compost (Scott, de Wilde and Boelens). Disintegration deals with the compatibility of composting municipal waste and its complete physical disintegration at the end of an industrial composting cycle. Levels of contaminants in the final compost have to fall below standard limits to obtain satisfactory compost quality. Latter can be tested by ecotoxicity tests which are done via the cress and summer barley germination- and growth test (guidelines available from Bundesgütegemeinschaft in Germany), earthworm acute toxicity test and the

aquatic toxicity test with Daphia pulex (OECD guidelines). These tests ensure the compost to be free of health hazards (de Wilde and Boelens).

1.6 Biosafety concern by transgenic plants and necessity of growth control / physical isolation

Dramatic incidents caused by the companies StarLink and ProdiGene regarding ‘pharm crop’ seed dispersal around a test field rose awareness of transgenic crops in public and the Food and Drug Administration (FDA). Scientists recognized that the spread of transgenes (i.e. PHA genes) through seed dispersal by animal or human activities or by natural pollination with transgenic pollen could severely interfere with human health. Although it seemed extremely unlikely that industrial or pharmaceutical products from crops increase plant fitness or damage the population structure of insects or other animals, no plants would be used for food or feed as experimental hosts as the risk of contaminating the food chain would be too high (Mascia and Flavell).

USDA (US Department of Agriculture) made clear that industrial and pharmaceutical

products must be grown under very strictly controlled conditions to avoid the genetic and mechanical mixing of material carrying the industrial trait into conventional breeding material by stray pollen. APHIS (Animal and Plant Health Inspection Service) even alleged that alphalpa and canola were inappropriate hosts as they would be bee-pollinated, showed multiple-year seed dormancy, and were sexually compatible with weed species of the field site (Mascia and Flavell).

1.7 Future expectations on bioplastic

In the short and medium terms, biopolymers will primarily be employed in areas in which biodegradability is of immediate consequence (medicine (osteosynthetic materials in the stimulation of bone growth, bone plates, sutures, blood vessel replacements), farming, packaging material (packaging film, garbage sacks, shopping bags) and disposable items (razors, feminine hygiene products, diapers, cosmetic containers, shampoo bottles and cups))