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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Directory of Open Access Journals eXPRESS Polymer Letters Vol.8, No.11 (2014) 791–808 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2014.82 Polyhydroxyalkanoate (PHA): Review of synthesis, characteristics, processing and potential applications in packaging E. Bugnicourt1, P. Cinelli2, A. Lazzeri2, V. Alvarez3* 1Innovació i Recerca Industrial i Sostenible (IRIS), Parc Mediterrani de la Tecnologia Avda. Carl Friedrich Gauss No. 11, 08860 Castelldefels (Barcelona), Spain 2UdR Consortium INSTM - Department of Civil and Industrial Engineering, University of Pisa, Largo Lucio Lazzarino 1, 56126 Pisa, Italy 3INTEMA, Composite Materials Group (CoMP), Engineering Faculty, National University of Mar del Plata, Juan B. Justo 4302 (B7608FDQ) Mar del Plata, Argentina Received 5 February 2014; accepted in revised form 4 June 2014 Abstract. Polyhydroxyalkanoates (PHAs) are gaining increasing attention in the biodegradable polymer market due to their promising properties such as high biodegradability in different environments, not just in composting plants, and pro- cessing versatility. Indeed among biopolymers, these biogenic polyesters represent a potential sustainable replacement for fossil fuel-based thermoplastics. Most commercially available PHAs are obtained with pure microbial cultures grown on renewable feedstocks (i.e. glucose) under sterile conditions but recent research studies focus on the use of wastes as growth media. PHA can be extracted from the bacteria cell and then formulated and processed by extrusion for production of rigid and flexible plastic suitable not just for the most assessed medical applications but also considered for applications includ- ing packaging, moulded goods, paper coatings, non-woven fabrics, adhesives, films and performance additives. The present paper reviews the different classes of PHAs, their main properties, processing aspects, commercially available ones, as well as limitations and related improvements being researched, with specific focus on potential applications of PHAs in packag- ing. Keywords: biodegradable polymers, biopolymers, polyhydroxyalkanoates (PHAs), polyhydroxybutyrate 1. Introduction and an increasing range of applications that bio Biopolymers or organic plastics are a form of plas- plastic produced from them can fulfil. The possible tics derived from renewable biomass sources such sources range from different types biomass (Fig- as vegetable oil, starch, proteins etc, unlike fossil- ure 1) including proteins (from animal and vegetal fuel plastics which are derived from petroleum. sources which are gaining interest due to their high Biopolymers provide the dual advantages of con- functionality and excellent properties) [1] lipids and servation of fossil resources and reduction in CO2 polysaccharides (e.g. starch and cellulose based emissions, which make them an important innova- biopolymers). tion of sustainable development. Others include bio-based polymers obtained from In recent years more and more biopolymers have bio-derived monomers, e.g. from corn, which are been studied by researchers revealing a large range of then polymerized through standard routes. This is possible sources from which they can be obtained the case for biopolyesters such as polylactic acid *Corresponding author, e-mail: [email protected] © BME-PT 791 Bugnicourt et al. – eXPRESS Polymer Letters Vol.8, No.11 (2014) 791–808 Main classes of biobased and biodegradable polymers From From From biomass microorganisms biotechnology PHA Polyactides Protein Lipids Polysaccharide PHB POlyacticacid Gelatin/Collagen Triglycerides Starch Casein Crosslinked triglycerides Cellulose Whey Rape seed oil carboxymethylcellulose Albumen Soy bean oil Chitosan hyaluronic acid Feathermeal Alginate Zein Soy Gluten meal Peanets Figure 1. Different classes of polymers which are biobased and biodegradable (therefore not including biodegradable plas- tics from petrochemical resources and non biodegradable partly or fully biosourced plastics) (PLA), until recently the most widely available the academic level and have not yet penetrated the biopolymer on the market, and set to be out ranked industry [2]. by bio-based polyethylene therephtalate (PET) or While polymers synthesized by (micro) algae are in polyethylene (PE), among others, also obtained via their infancy, once they are moved into commer- a similar synthesis route. In contrast, polyhydrox- cialization they are likely to find applications in a yalkanoates (PHAs) are biogenic polyesters that wide range of industries. Other possible routes for can be naturally accumulated in microbial cultures. the use of algae derived monomers for subsequently Among this latter category, obtained via so called synthesizing PLA are also being investigated and bio-refineries, algae serve as an excellent pathway composites including algae derived natural fibres in for plastic production owing to their numerous their formulations are now commercially available. advantages such as high yield and the ability to Bioplastics are generating increasing interest, for grow in a range of environments. Algae biopoly- industries and their market is rising as a result of mers mainly evolved as a by-product of algae bio- technological advances and cost reductions. The fuel production, where companies were exploring advantages of bioplastics over traditional plastics alternative sources of revenue in addition to those are unprecedented, provided that they are used in obtained from the biofuels. Moreover the use of situations in which they enable improved function- algae opens up the possibility of utilizing carbon, ality and generate extra benefits. Biopolymers, from neutralizing greenhouse gas emissions from facto- which bioplastics are produced, are generally more ries or power plants. Algae based plastics have been sustainable materials than their petrochemical-based a recent trend in the era of bioplastics compared to counterparts, and, as previously mentioned, they traditional methods of utilizing feedstock, such as can be produced from a wide range of renewable starch from corn and potatoes, in polymers produc- resources including more and more wastes and non- tion, and plastic formulations. food competing sources as opposed to early bio - Various processes for the cultivation of algae and polymers which diverted full corn fields for the pro- production of biopolymers exist. Fundamentally, duction of starch as raw material for polymers pro- they comprise two stages: a first stage, in which duction, that coupled with the production of ethanol. algae growth is initiated and a second stage where The practical side of the use of biopolymers is related the biopolymer accumulation is promoted. Although to the economic advantage for industries and munic- increasing research on the use of microalgae for ipalities. These consist of the saving of raw materi- such production, e.g. PHA, most studies are still at als and the reduction in costs when the products are 792 Bugnicourt et al. – eXPRESS Polymer Letters Vol.8, No.11 (2014) 791–808 finally discarded. Renewable biologically degrad- barrier properties, PHAs offer great potential for able products also contribute to a sustainable econ- packaging applications. Their properties, capacities omy. This means that the agricultural sector obtains for deriving a range of compounds with variable the possibility to get a rising percentage of its addi- behaviour, processability, as well as the state of aca- tional turnover from non-food products. After the demic developments and current shortcomings, com- disposal of the products, the recovered materials mercially available products and applications are can be taken back by the agriculture as certificate reviewed hereafter. quality-compost with economical (and ecological) advantages. 2. Polyhydroxyalkanoate polymers Packaging is the biggest polymer processing indus- Due to their previously discussed benefits, interest try with the food sector being its principal customer. in biodegradable polymers produced from renewable Despite environmental problems, the European resources has increased significantly in recent years. polymer packaging market is increasing in the order Polyhydroxyalkanoate polymers are naturally pro- of millions of tons per year. In the wake of future duced by bacteria in general cultivated on agricul- laws in relation to reducing the weight and volume tural raw materials. They can be processed to make of these products, cheap and biodegradable poly- a variety of useful products, where their biodegrad- meric products are receiving growing attention in ability and naturalness are quite beneficial in partic- this market [3]. The materials used for this applica- ular for application in single use packaging and tion often have short service time, so they end up agriculture. mostly in landfills and stay there for over 100 years Poly(3-hydroxybutyrate) (PHB), Figure 2a, is a ([4–8]). When products, such as bags and bottles, homo polymer of 3-hydroxybutyrate and is the most are discarded, it is not possible in several cases, to widespread and best characterized member of the collect them, and can end up clogging sewers and polyhydroxy-alkanoate family. Other members of drains, and polluting streets, beaches and scenery, family are displayed in Figures 2b and 2c. having a very costly impact on waste management. Poly-3-hydroxybutyrate (PHB) is a linear polyester Plastic pollution is
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