Effect of the Injection Moulding Processing Conditions on Biopolymers Final Properties

This research work intended to study the effect of the main injection moulding parameters in the final properties of biopolymers mouldings. An experimental procedure was carried out in which four biopolymers containing different composition percentages of poly-lactic acid (PLA) and plasticized starch (PLS) were compared with polypropylene (PP). For each material the effect of the processing conditions (mould temperature, injection temperature and holding pressure) on the final properties was discussed and the possibility of using biopolymers as a substitute of PP in household utility products was evaluated. Introduction The environmental pollution problems caused by the use of synthetic polymers based on petrochemicals, has given an extensive space and an attracted interest to the development of environmental friendly polymeric materials [1-6]. Plasticized starch (PLS) emerged as a potentially useful material for biodegradable plastics because of its natural abundance and low cost, being corn, wheat, potato and rice the main sources of starch [7]. PLS offers an interesting alternative for synthetic polymers where long-term durability is not a requirement and rapid degradation is an advantage [8-10]. For some applications, these materials have limited mechanical properties, but an increase of tensile strength can be achieved by compounding them with other biodegradable products [6,11-13]. Polylactide Acid (PLA) is one of the elected biodegradable products for this purpose, since it has good mechanical properties, easy processability and excellent degradability. So, currently, PLA is regarded as one of the most promising biodegradable polymers and is expected to substitute some of the non-biodegradable engineering plastics. However, its high cost limits its application [6,12,14]. One of the most used technologies for processing synthetic petrochemicals based polymers is injection moulding. It provides high quality polymeric parts and, if a large production is intended, it makes them available at a quite reduced cost. The aim of this paper is to study the effect of the injection moulding processing conditions on the final properties of biopolymers mouldings. To achieve this goal, an experimental protocol was set-up. Four different biopolymers were processed, with different injection conditions as regards mould temperature, injection temperature and holding pressure, and the obtained mouldings were tested. The performed tests allowed to analyse the sensitivity of the mechanical properties of each material to each of the processing parameter, and to compare the behaviour between the materials. This work was developed with the cooperation of an SME company (FAPIL, S.A.). Its core business is currently centred in the production of a wide range of household cleaning utilities, like mops, buckets and brushes, made essentially of polypropylene (PP). The intention to launch new domestic products with a disposable nature, together with an increasing environmental consciousness introduced the need of understanding the behavior of biopolymers and get familiar with their processing conditions. Experimental Approach Materials. Based on a preliminary set of material requirements, ranging from the expected lifetime and normal working temperature to the need of resistance to contact with water and domestic cleaning fluids, biopolymers suppliers provided, as suitable for the application, four commercially available materials. The provided biopolymers, from three different suppliers, have a different mix contend of PLA and PLS, and shown in Table 1, and all were used in the injection moulding experimental tests. To establish a baseline for comparison purposes, Table 1 also presents the company most frequently used petrochemical based polymer. Supplier Material Code Melt Flow Index Melting Point Density Composition Total Petrochemicals PP 9020 PP 25 [g] /10 [min] 230oC / 2.16 kg 165 [oC] 0.905 [g/cm] 100% PP Biotec Bioplast GS 2189 90/10 20-40 [g] /10 [min] 190 oC / 2.16 kg 130 [oC] 1.2-1.4 [g/cm] ≈ 90% PLA ≈ 10% PLS Cabopol Biomind R006 80/20 20-40 [g] /10 [min] 190 oC / 2.16 kg 130 [oC] 1.2-1.3 [g/cm] ≈ 80% PLA ≈ 20% PLS Rodenburg Biopolymers Solanyl 35F 40/60 ~13 [g] /10 [min] 190 oC / 2.16 kg 140-145 [oC] 1.26-1.3 [g/cm] ≈ 40% PLA ≈ 60% PLS Cabopol Biomind C004 10/90 15-30 [g] /10 [min] 100 oC / 2.16 kg 90 [oC] 1.15-1.25 [g/cm] ≈ 10% PLA ≈ 90% PLS Table 1 – Material Specifications Processing. For each parametric combination (parameter setting), 20 specimens where produced. To avoid the effect of the stabilization period of the injection process, the first 10 were rejected and only the further 10 specimens were collected for evaluation. The injection parameter setting (based on materials suppliers’ information and literature review) can be seen in Table 2. Test variables Materials PP 90/10 80/20 40/60 10/90 Mold temperature [oC] 30 50 20 40 20 40 20 40 20 Injection temperature [oC] 210 230 250 140 160 140 160 150 170 100 120 Set Holding Pressure [bar] 16 25 30 48 30 48 30 48 30 48 Table 2 – Injection parameters setting Mechanical tests and Specimens. The evaluation of the mechanical properties was made based on tensile, flexural, impact and shrinkage tests. Table 3 and Figure 1 present the standards followed for testing procedures, when available, the measuring points for shrinkage evaluation and the geometry of the injected specimens. Test Standard Specimen Tensile NP-1198 (1976) Flexural ASTM D790 – 03