Joining Bioplastics
Joining Bioplastics Biobased hotmelt adhesives for paper and cardboard packaging By: Birgit Kießler and Martin Zahel Papiertechnische Stiftung (PTS) Dresden, Germany The traditional paper production and processing industry has always been operating in a largely bio-economically manner as it primarily uses the renewable resource of wood and extracted cellulose fibres. Paper is therefore an already comparatively sustainable, value-adding material based on renewable raw materials of low quality. It has long been a shining example of material cascade utilization through multiple recycling. At the same time, the fibre base is also biodegradable in principle. However, a large share of auxiliary materials for the production and converting of paper, such as barrier coatings, coating colour binders, adhesives, retention or wet strength agents consist in many cases of fossil-based polymers. In paper recycling, these materials are largely discharged as rejects, which are often used thermally. In addition to the associated release of fossil CO 2 into the atmosphere, such materials are often characterized by unfavourable biodegradability, which generally means that there is a potential for the formation of microplastics. One important segment in the fast-growing paper packaging market is hotmelt adhesives. Those components are defined as thermally fusible adhesive systems that develop cohesion (internal strength) through cooling. They are 100 % solids and free of solvents. Due to their very good properties and unrivalled price-performance ratio, conventional hotmelt adhesives are currently produced almost exclusively from petrochemical base components. The versatility and good processability of hotmelt adhesives open a wide range of applications inside and outside the paper industry. Each of these applications has a specific requirement profile, which means that there are no universal raw materials or formulations for hotmelt adhesives. However, typical formulations consist of three main components: • polymers – that are responsible for overall strength properties and viscosity • tackifying resins – making the molten state stickier • and wax – controlling the open time and set speed In addition, other minor additives ensure the stability of the hotmelt adhesives and have strength-enhancing properties. Biobased alternatives for tackifying resins and waxes are available in the form of tree resins or tree resin derivatives and vegetable waxes, e.g., from sugar cane. By blending these biobased base components with the typical synthetic copolymer ethylene vinyl acetate (EVA), a biobased content of 50 % can be achieved. A further increase requires the use of a biobased polymer. Together with IPF (Leibniz Institute for Polymer Research, Dresden, Germany) and a large industrial consortium, PTS developed a starch-based hotmelt adhesive within the Glykopack project of the German FNR (Agency for Renewable Resources). The first step was to make a pre-selection of biobased raw materials able to meet and adjust the various properties of a hotmelt. Based on a range of various thermoplastic starch blends and other starch products, such as dextrin, a large selection of formulations with highly different components was produced. The final goal was to find appropriate sustainable/renewable resources capable of serving as substitutes for petroleum-based or synthetically made ingredients. Said first trial formulations were tested for adhesive strength, softening temperature, melting behaviour, degradation, and other properties. In addition, the most promising formulations were subjected to tests on recyclability, migration tendency of toxicologically questionable hotmelt components via the packaging into the foodstuff, processing technology, and ageing in comparison with standard hotmelts. The recipe that proved successful in the end contained a thermoplastic-starch blend, colophony, and castor oil with 85 % biobased content. The achieved adhesive and cohesive strength properties showed to be competitive to conventional products (see diagram) and processability could meet industrial requirements. Cohesive strength Unfortunately, due to the high starch content in the developed formulation decomposition phenomena and insufficient homogenisation with the other hotmelt components were observed. The product showed discolouration and a reduction of viscosity after a longer load period at processing temperature (photo). Nevertheless, high thermostability is an important processing criterion, particularly for common high-temperature storage tank systems. For this purpose, several tests were performed with stabilizers under various conditions for decelerating or preventing such degradation, but without completely convincing success. In order to tackle these obstacles, PTS and IPF just started a new IGF research project (German Federal Ministry for Economic Affairs And Energy – BMWi) called BioGlyk. The aim of the present research project is to ensure the thermostability necessary for the industrial applicability of starch-based hotmelt adhesives. To this end, an investigation of a novel formulation containing starch derivatives like starch esters as base polymers and 36 bioplastics MAGAZINE [03/21] Vol. 16
Joining Bioplastics nanoscale starch particles as an additional reinforcing component is planned. The material concept will be supplemented by an efficient form of manufacturing technology using an extrusion approach. Following this path, a 95 % biobased formulation should be generated. The research is being funded by BMEL and BMWi within the projects FNR 22005515 “Glykopack“ and IGF 21877 BG “BioGlyk.“ www.ptspaper.de pulling force [N] 200,0 180,0 160,0 140,0 120,0 100,0 80,0 60,0 40,0 20,0 0,0 Pulling force pressing time diagram 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,9 2 pressing time [s] Biobased hotmelt 1 Biobased hotmelt 2 Standard hotmelt Composting of diapers Ontex (Aalst, Belgium) and circular economy company Les Alchimistes (Pantin, France) announced their collaboration to test the compostability of diaper pads. “Our goal is to make the separate collection and composting of used, compostable diapers a reality,” said Maïwenn Mollet, director of the Fertile Diapers program at Les Alchimistes. “We are very happy that Ontex and their brand Little Big Change are joining our mission. Ontex has the engineering knowledge and resources to design diapers that can be compostable. Our goal is to create a new circular economy loop with Ontex and other like-minded companies and to compost 500 million diapers by 2030.” Ontex and Les Alchimistes have set up a pilot project at Les Alchimistes’ industrial composting site near Paris with the aim of proving that composting of Ontex diaper pads is possible, and that waste and incineration can be reduced. The project requires cooperation between different partners: from suppliers of materials, diaper manufacturers like Ontex, to waste collection and to composting partners using suitable technology. “Together with partner company gDiapers, which has 17 years of expertise in hybrid compostable diapers, the Ontex Little Big Change brand has developed a new diaper system. The system consists of a reusable outer diaper made of cotton and a disposable diaper pad which is designed to be industrially compostable,” said Annick De Poorter, Executive Vice President R&D, Quality and Sustainability, Ontex. The insert itself is plant-based, does not contain any lotions, perfumes, and has totally chlorine-free FSC ® certified fluff pulp. The pads used in Paris are produced in a certified CO 2 neutral way. The film is made of compostable plastics, such as polylactic acid (PLA) and starch-based film material, as a spokesperson of Ontex explained to bioplastics MAGAZINE. Currently, tests are underway about the compostability of the SAP (superabsorbent pad) use in the diapers. “We are now testing if the diaper pads can be composted on an industrial scale by working together with a test group of 30 families in Paris who subscribe to Ontex’s baby diaper service Little Big Change,” Annick de Poorter continued. The announcement of the industrial-scale composting test with Les Alchimistes follows the news of Ontex’s collaboration with Woosh, a Belgian start-up that is on a mission to recycle diaper waste into raw materials and, in doing so, create a large-scale solution for diaper recycling. Although Woosh takes a different approach to the one adopted by Les Alchimistes (focusing on recycling rather than composting) both projects fit with Ontex’s ambitions and sustainability strategy for 2030 to reduce diaper waste through different technologies. “As a major player in essential personal hygiene, we recognize the need to find alternatives to landfill and incineration for our used products. We are examining ways to reduce CO 2 emissions all through their different life cycle phases. As we ourselves move towards a circular economy business model, it is a natural and logical step to work together with other companies to make our diapers more recyclable or compostable. We support Les Alchimistes’ mission to learn how diapers can be composted and are eager to discover the results of the tests,” says Annick De Poorter. MT www.ontex.com Application News bioplastics MAGAZINE [03/21] Vol. 16 37
