From Science & Research
From Science & Research From coffee grounds to plastic Introduction Europe is one of the largest importers of coffee. However, currently industrial utilization of the coffee grounds generated during production is carried out only to a limited extent [1], [2]. Some companies already have recognized the potential of the “coffee ground” residue and have even brought plastic products to the market containing coffee grounds (3D printing filaments, cappuccino cups, yarns, etc. [3] [4] [5]). However, there are no (biobased) plastic compounds containing coffee grounds commercially available on the market, which are suitable for processing methods like injection molding or extrusion blow molding. In a first feasibility study in 2016, the processing as well as the effect of the residues on biobased polymers were analyzed at the IfBB - Institute for Bioplastics and Biocomposites, University of Applied Sciences and Arts Hanover [2]. To save fossil raw materials like crude oil, coffee grounds have been primarily used as a filler to substitute conventional polymers. Furthermore, the residues were used as a colouring agent in different kinds of polymers. In the current project, novel fully biobased composites, especially for applications such as coffee consumer goods, computer accessories and for the office sector are being developed and modified. Used material The additivation of the coffee grounds was carried out in a PLA matrix (injection molding type). Other additives such as an impact modifier (IPM) and wood fibers (NF) were also used to enhance the performance (improved load transmission through fiber reinforcement) and appearance. Coffee Grounds Large differences in the particle size or agglutination of the coffee grounds leads to agglomeration during extrusion, as previous studies show. Therefore, a non-homogenous dosage of the coffee grounds into plastic would hinder an industrial processing [2]. For an optimized process and to control, as well as to determine, material properties (stiffness, strength, crystallization, etc.), the quality control of particle size and distribution of the coffee grounds are decisive. Figure 1: SEM image (magnification: 100X) PLA + Coffee grounds + NF coffee grounds NF 44 bioplastics MAGAZINE [04/18] Vol. 13
From Science & Research By: Daniela Jahn, Sebastian Spierling, Andrea Siebert-Raths IfBB – Institute for Bioplastics and Biocomposites, Hanover University of Applied Sciences and Arts – IfBB Hanover, Germany Experimental Procedure For extrusion processing, a technical co-rotating KraussMaffei twin-screw extruder ZE 34 Basic was used. The matrix and impact modifier were added at the beginning of the extruder in the melting zone. The dosage of coffee grounds and natural fibers was conducted via a side feeder unit. Adapted screw configurations enabled a cautious incorporation without damaging the PLA, the residue or the fibers. Due to specific screw configurations, predrying of the material was not required, i.e. prior opened vacuum degassing extracts the remaining humidity during the process. For production of test specimens via injection moulding, a KraussMaffei KM50-180 AX injection moulding machine was used (tensile test bars type 1A DIN EN ISO 527).To prevent molecular chain degradation by hydrolysis, pellets were dried before processing under 500 ppm) [6]. Subsequently, the microstructures and mechanical and thermal-mechanical properties of the coffee ground compounds were determined. Material Properties To analyze the connection of coffee particles and natural fibers in the PLA, the samples were analyzed by scanning electron microscopy (SEM). Figure 1 shows the coffee particles and natural fibers fully embedded in the PLA matrix. Thus, a good fiber-matrix adhesion, which results in an optimized load transmission of the fibers/coffee particles under mechanical loads, could be realized. As known from the literature, by adding fillers or fibers as a function of the concentration the flowability (MFR) and impact strength is reduced. By implication, the tensile modulus is increased [7]. The situation is similar with the coffee grounds used (Figure 2). Both with coffee grounds and with natural fibers, the impact strengths are reduced, which in turn increased the tensile modulus of elasticity. Due to the addition of particles and fibers, a reduction in the cycle time during the injection molding process was identified for all the materials. This positive effect suggests that the crystallinity (K) of the materials was increased. Figure 2: Thermomechanical properties of coffee grounds compounds Tensile strength 150% PLA Cycle time 100% 50% Tensile modulus PLA + Coffee grounds PLA + 10% NF 0% HDT-B Impact strength PLA + 10% Coffee grounds + 10% NF PLA + 10% Coffee grounds + 10% NF + 8% IPM MFR bioplastics MAGAZINE [04/18] Vol. 13 45
