Additives/Masterbatches Masterbatches of novel additives for bioplastics Biopolymers – together with polymers from CO 2 and recycled materials – are one of the future pillars of a sustainable chemical and plastics industry. Replacing fossil raw materials such as crude oil, natural gas and coal with renewable carbon will help traditionally fossil carbon-focused industries transition to sustainability [1]. The factor sustainability for biopolymers alone is not sufficient – it has to be accompanied by performance, regulatory and economic attributes. Masterbatching using appropriate plastic additives and smart processing is one approach to achieve this. The Global Bioplastic market As the demand for more environment-friendly and sustainable biopolymers is rising, the market for bioplastics is continuously growing and diversifying. The global bioplastics production capacity is set to increase from around 2.15 million tonnes in 2020 to 2.4 million tonnes in 2024. The bioplastic market is categorized into rigid packaging, flexible packaging, textiles, automotive, agriculture and horticulture, coating and adhesives, consumer goods, and others. Packaging remains the largest field of application for bioplastics with more than 53 % of the total bioplastics market in 2019 [2]. Plastic additives basics An important part of the final properties and aspect of polymers depends on the additives combined with the polymers during processing. To develop bioplastics, any additives must be also more sustainable [2]. The most common additives include fillers, pigments, plasticizers, stabilizers, flame retardants, food contact and medical additives, nucleating agents and colour/ pigments. Additives are generally introduced via concentrated mixtures of pigments and/or additives in carrier resins in normal polymer pellet shape known as masterbatches. Masterbatch added to main resin prior to processing Masterbatches enable additives to be used during plastics manufacturing without the issues of handling small amounts of pure ingredients, including dust, accurate dosing, and the shelf life of active substances. Additives for bioplastics Biopolymers are rarely used on their own to make products. Different additives are generally blended with the virgin bioresin to obtain similar performance properties to conventional plastics. Depending on the application, the end of life plays a major role in the choice of additives for biodegradable bioplastics. The additives can be separated in three categories: • Traditional additives, with no adverse effects on health and environment. • Renewable additives derived from natural sources, which are not necessarily biodegradable. • Renewable and biodegradable additives. They can be used for single-use, short-lived products, or compostable polymers. Renewable and biodegradable additives Scion’s work over the past 15 years has focused on investigating renewable and biodegradable additives that can be added to bioplastics to manufacture products with tailored functionalities. The advantages of using renewable and biodegradable additives include aiding the processability of polymers such as polyhydroxyalkanoates (PHAs), changing mechanical properties of materials, modifying in-use disintegration rates of final products, adding nutrients to soil/ compost upon biodegradation and reducing the amounts of bioplastics used. In addition, side-streams from the agri-food sector can be recycled into useful additives to improve targeted properties of bioplastics prior to eventual composting of the end products. The challenges of renewable and biodegradable additives The heat and moisture sensitivity of many renewable and biodegradable additives, such as natural fibres, make their processability technically challenging. Biobased fillers are much more sensitive than commonly used additives. Processing conditions, such as extruder screw design, filler dispersion, temperature profiles and vacuum/venting position, play a major role in the final properties of the bioplastic. Nevertheless, developing new additives is an opportunity to create totally new value chains using biomass side-streams. A further challenge is transitioning from laboratory and pilot scale to industrial scale processing. When masterbatching is necessary to meet the scale for industrial processes, finding 20 bioplastics MAGAZINE [03/20] Vol. 15
Additives/Masterbatches By: Regis Risani, Florian H.M. Graichen and Dawn A. Smith Scion Rotorua, New Zealand a compounder to process novel biomaterials can be difficult. Often, traditional compounders or masterbatching companies are reluctant to experiment with new materials and unwilling or unable to change extruder screw design and/or introduce/ move vacuum venting to lines that traditionally process pigment or other additives and are optimised for mixing and dispersion of these additives. When a brand owner and a converter are inclined to process material with novel additives but no compounder is willing to optimise their extruders to process these materials; masterbatching at pilot scale extrusion facilities becomes an option. Pilot scale extrusion facilities often offer more flexibility as they are used to optimise a wide array of processes. Masterbatching, as opposed to compounding, is a means to meet the scale needed for industrial processes. Examples of biomass side-streams that present challenges for traditional processors include: • Blood and bone meal; a by-product from the meat processing industry that is rich in nitrogen and phosphorus and can add fertiliser during biodegradation BUT has a very strong smell, especially at slightly elevated temperatures • Grape marc/pomace from wine production; mainly composed of skins and seeds that can aide moisture and microbial ingress into materials as they biodegrade BUT is extremely high in moisture content and needs either predrying or vacuum venting during processing • Wood fibres (not wood particulates) can be used for mechanical improvement of materials without raising density; however, traditional extrusion processes reduce fibre length due to harsh screw designs, and vacuum venting is required to deal with residual moisture in fibres. At Scion, experts have successfully produced masterbatches using the above and other problematic biomasses, enabling further plastics processing in injection moulding and sheet extrusion. Masterbatching to overcome challenges Flexible pilot scale twin screw extruders equipped with vacuum ports and vacuum crammers and the ability to modify and optimise screw designs based on extrusion modelling enable the production of masterbatches with at least 60 wt% biomass. This enables direct addition of biomass fillers during plastics processing/converting. Extruded sheet with 10 % biomass filler Masterbatches may need to be added at addition rates higher than normal colour/additive masterbatches, depending on desired filler concentrations. Converters are accustomed to handling masterbatch addition rates of up to 5 % masterbatch. However, some addition rates for current industrial processes can be up to 40 %. It is important to check the capability of the converter when discussing utilisation of masterbatches at higher addition rates. Biomass-filled bioplastics enabled through masterbatching Along with other organisations worldwide, Scion has focused on specialised extrusion equipment and capability to deliver innovative, renewable materials from laboratory to pilot scale. In the area of new biobased and biodegradable additives originating from biomass side-streams, many sources remain insufficiently exploited. The demand of bioadditives is increasing worldwide. In the context of a circular bioeconomy, using life-cycle methodology to assess the environmental impacts associated with bioplastics made using renewable and biodegradable additives is a green marketing tool. The cradle to cradle cycle mimics the natural system where organism waste becomes valuable nutrients. It is a complex but very powerful business strategy to promote the development of biomass-filled bioplastics. Using biomass feedstock as a new source of additives is a challenging but also terrific way to develop a circular bioeconomy around bioplastics, and masterbatching is a means to enable the utilisation of a wide array of additives. References: [1] https://www.european-bioplastics.org/nova-institute-explores-ways-toachieve-a-renewable-carbon-chemical-industry-in-the-european-union/. [2] https://www.european-bioplastics.org/market/. www.scionresearch.com Extruded sheet with 10 % biomass filler bioplastics MAGAZINE [03/20] Vol. 15 21
