POLYHYDROXYALKANOATES: PLASTIC THE WAY NATURE INTENDED? INDUSTRIAL AND ENERGY POLYHYDROXYALKANOATES: PLASTIC THE WAY NATURE INTENDED? WHITE PAPER EXECUTIVE SUMMARY Plastic accumulation in the natural environment is one of the most visible forms of environmental pollution caused by business. As a result of continual exposure to images of oceans full of plastic, consumers are becoming increasingly concerned about single-use disposable plastic items and plastic packaging. For brands and manufacturers, the search is on for alternatives in a wide range of applications. In particular, the superior to conventional plastics – solutions that bring all of the cost, high temperature performance of PHAs significantly extends marketing and convenience benefits of plastic, without the the addressable number of applications for bioplastics, environmental baggage. beyond those which can be served by the most common bioplastic PLA. Polyhyroxyalkanoates (PHAs) are a class of bio-derived, biodegradable polymers which could fit the bill. PHAs provide With costs now approaching parity with conventional a tunable property set which provides unparalleled potential polymers, overcoming manufacturing challenges is the last for a bioplastic to substitute fossil fuel derived plastics major hurdle preventing wide scale adoption of PHAs. 01 WHITE PAPER POLYHYDROXYALKANOATES: PLASTIC THE WAY NATURE INTENDED? PHAS ARE BIO-BASED, BIODEGRADABLE Bioplastics are bio-based, biodegradable or both (European Bioplastics) PLASTICS, PRODUCED BY FERMENTATION FROM BIO-BASED A RANGE OF FEEDSTOCKS, INCLUDING WASTE. Are bio-based Are biodegradable and bio-based The term bioplastics is an umbrella term which describes: Bioplastics Bioplastics e.g. Bio-based PE e.g. PLA, PET, PTT PHA, PBS, conventional polymers derived all or in part using drop-in, Starch blends bio-based feedstocks, NOT BIODEGRADABLE BIODEGRADABLE polymers which are fossil fuel derived but are biodegradable Conventional plastics Bioplastics nearly all conventional e.g. PBAR, PCL plastics e.g. PBAR, PCL polymers which are both bio-derived and biodegradable. Polyhydroxyalkanoates or PHAs are an emerging class of Are biodegradable bioplastics in the latter category, i.e. they are bio-based and biodegradeable. PHAs are produced by bacterial fermentation using bio-derived feedstocks – including waste – and thus are Figure 1: Types of bioplastics. Reproduced with permission from an alternative to fossil fuel-derived plastics. European Bioplastics https://www.european-bioplastics.org/ Input for plant growth Input for production WASTE OR BIO-BASED FEEDSTOCKS COMPOST ENERGY Fermentation Incineration or anaerobic digestion PHA-ENRICHED Compositing BACTERIA PRODUCTS PHA BIOPLASTIC Reuse Refining Product manufacture Figure 2: PHA lifecycle 02 POLYHYDROXYALKANOATES: PLASTIC THE WAY NATURE INTENDED? WHITE PAPER THERE ARE MANY DIFFERENT PHAS WITH A VERY produced PHAs are limited to using P3HB and one other WIDE RANGE OF PROPERTIES, EXPANDING THE PHA as the co-monomer (the other monomer present in the RANGE OF APPLICATIONS BEYOND THOSE THAT copolymer). CAN BE SERVED BY MORE COMMON BIOPLASTICS. These various PHAs have a wide range of properties which can be tailored to different applications. In general, PHAs are The chemical composition of PHAs can be tuned depending biodegradable, compostable thermoplastics. on the monomer subunits used and in which combinations. PHAs are produced either as homopolymers or copolymers. Because the PHA family contains a wide variety of different Homopolymers consist of one type of PHA throughout polymers which can be co-polymerised and blended, the the entire structure – such as pure P3HB or P4HB (see design space of this material class is very large. Figure 4 and Figure 1). Copolymers on the other hand are made up of two Figure 5 show the most important thermal and mechanical or more different PHAs, randomly distributed throughout the properties of the PHA family with respect to other common structure of the polymer chain. Most common industrially consumer polymers. H C H C O 3 O 3 CH O 3 H O OH P(3HB-co-4HB) H3C m n O CH3 O H PHBHp O CH O PHBO O CH O PHBOd CH 3 3 3 O O OH H H m n O CH3 O O O OH O O OH H m n m n O O OH PHBV H C m n 3 H C Copolymers 3 CH3 H3C CH3 CH3 O CH O O CH3 O O O 3 O H O O H O PHBH PHBD H PHVVB OH H P(3HO-3HH) O O OH O O O O OH m n O O OH m n CH p 3 m n m n Short Chain Length (SCLs) Medium Chain Length (MCLs) INCREASING CHAIN LENGTH CH O H 3 O OH P3HB n O O Homopolymers H OH P4HB n Figure 3: The PHA family POLYMER CODE POLYMER NAME MATERIAL CLASS PROPERTIES P3HB Poly(3-hydroxybutyrate) Semi-crystalline thermoplastic Strong Brittle Small thermal processing window High softening temperature P4HB Poly(4-hydroxybutyrate) Thermoplastic elastomer Strong Flexible Ductile High melt viscosity P(3HB-co-4HB) Poly(3-hydroxybutyrate-co-4- Semi-crystalline thermoplastic/ Strong hydroxybutyrate) thermoplastic elastomer Tough Large thermal processing window Ductile PHBV Poly(3-hydroxyalkanoate-3- Semi-crystalline thermoplastic Strong hydroxyvalerate) Brittle Large thermal processing window High softening temperature PBHH Poly(3-hydroxybutyrate- Semi-crystalline thermoplastic Flexible hexanoate) Ductile Easy to process Low softening and melting temperature Table 1: Summary of properties of some common PHAs 03 WHITE PAPER POLYHYDROXYALKANOATES: PLASTIC THE WAY NATURE INTENDED? Acrylonitrile-Butiadene-Styrene – ABS 3.5 High Density Poly(ethylene) – HDPE PLA Low Density Poly(ethylene) – LDPE Poly(amide) 6 – PA6 PVC Poly(carbonate) – PC 3 PET Poly(ethylene terephthalate) – PET PS Poly(ethylene terephthalate) Glycol Modidified – PETG Poly(hydroxyalkanoates) – PHAs 2.5 PMMA Poly(lactic acid) – PLA ) ABS Poly(methylmethacrylate) – PMMA a PC Poly(propylene) – PP Poly(styrene) – PS PETG 2 Poly(vynil chloride) – PVC Thermoplastic Starch – TPS PHAs PP 1.5 TENSILE MODULUS (GP HDPE 1 PA6 TPS Stiff 0.5 Flexible LDPE 0 40 60 80 100 120 140 160 MAXIMUM OPERATING TEMPERATURE (˚C) Figure 4: The PHA thermomechanical design space for stiffness (tensile modulus) against maximum operating temperature. Other oil based (orange) and bio based (blue) thermoplastic design spaces have been included for comparison Acrylonitrile-Butiadene-Styrene – ABS High Density Poly(ethylene) – HDPE HDPE 1000 Low Density Poly(ethylene) – LDPE Poly(amide) 6 – PA6 Poly(carbonate) – PC Poly(ethylene terephthalate) – PET Poly(ethylene terephthalate) Glycol Modidified – PETG LDPE Poly(hydroxyalkanoates) – PHAs Poly(lactic acid) – PLA Poly(methylmethacrylate) – PMMA 100 PETG Poly(propylene) – PP PC Poly(styrene) – PS PVC PET Poly(vynil chloride) – PVC PP PA6 Thermoplastic Starch – TPS PHAs TPS ABS ELONGATION AT BREAK (%) AT ELONGATION Ductile 10 Brittle PLA PMMA PS 1 0 20 40 60 80 TENSILE STRENGTH (MPa) Figure 5: The PHA mechanical design space for elongation at break against tensile strength. Other oil based (orange) and bio based (blue) thermoplastic design spaces have been included for comparison 04 POLYHYDROXYALKANOATES: PLASTIC THE WAY NATURE INTENDED? WHITE PAPER PHAS COULD SUBSTITUTE CONVENTIONAL cannot be made from compostable plastics. In fact, as we PLASTICS IN A WIDE RANGE OF APPLICATIONS. illustrate in Figure 7, compostable plastics can be suitable for manufacturing products with a range of life expectancies END OF LIFE CONSIDERATIONS ARE AN from disposable to products designed to last for a significant IMPORTANT FACTOR IN DETERMINING WHICH number of years such as automotive components and toys. APPLICATIONS ARE SUITABLE. PHA manufacturers are developing a diverse range of end markets, including environmental services, automotive, electronics and energy. The versatility of PHAs lends them to a wide range of potential market applications. The main markets where End-of-life considerations are important when considering PHAs have already achieved some degree of penetration are which applications are suitable for designing with PHA. packaging, food service, agriculture and medical products. PHA products can either be designed to enter the natural PHAs are penetrating in both low value, high volume markets environment (e.g. mulching films ploughed back into the (such as compost bin liners) as well as low volume, high soil) or to be treated in industrial composting facilities. Care value markets (such as absorbable surgical film). Figure 6 must be taken not to contaminate existing recycling systems illustrates a number of the current and future applications for conventional polymers; for this reason PHAs would not be of PHAs. A common misconception is that durable products suitable replacements for PET water bottles. CURRENT FUTURE Refuse sacks, compost bin liners, carrier bags, PACKAGING gift bags, shrink wrap Bottles, laminate foils Disposable gloves, disposable aprons, liners for FOOD SERVICE Food containers and utensils coffee cups, foam packaging Mulching film, plant pots AGRICULTURE Slow release of fertilizers, etc. into soil Microencapsulation, slow release drug formulations, Absorbable sutures, absorbable mesh, absorbable MEDICAL cartilage engineering, stents, wound dressings, bone plates, surgical film, composite mesh high performance filters, syringes, gowns, gloves Phone case, furniture CONSUMER PRODUCTS Sanitary goods, wipes, textiles, toys, cosmetics (microbeads), interior design Plastic additives CHEMICALS Adhesives, paints, coatings, fine chemicals ENVIRONMENTAL SERVICES Oil slick remediation, denitrification (water treatment) AUTOMOTIVE Automotive parts ELECTRONICS Pressure sensors for