Injection Moulding
Injection Moulding Dimensional stability of injection moulded bioplastics During processing plastics, there are different fundamental factors that influence the quality of a component. A key factor for the injection moulding process is the dimensional stability. This describes how much the dimensions of the processed part deviate from the specified dimension after processing. In particular, problems often quickly arise here due to different shrinkage and warpage properties, once a new material, such as a bioplastic, should be used for an existing injection moulded component. At the Institute for Bioplastics and Biocomposites – IfBB, University of Applied Sciences and Arts, Hanover, various bioplastics were therefore investigated in more detail. The following marketable and commercially available materials were examined: material to be substituted, differs strongly in its shrinkage properties, this usually leads to processing problems and requires a corresponding adjustment of the cavity. It is therefore not possible to make the general statement that a slight shrinkage is good and a large shrinkage is bad. As a general rule, if the cavity should not be reconstructed to suit the material, the bioplastic should exhibit similar shrinkage behaviour as the petrochemical material to be substituted. In addition, when processing bioplastics – as well as conventional plastics – widely differing shrinkage properties in and across the direction of flow lead to component distortion. Table 1: Overview of the examined bioplastics for injection moulding applications Material Tmelt [°C] Tmold [°C] Holding pressure [bar] Flow Direction [%] Cross Direction [%] FD/CD Nature Works Ingeo 3052D 200 °C 30 °C 500 bar 0,247 0,315 0,784126984 Nature Works Ingeo 3251D 200 °C 30 °C 500 bar 0,242 0,28 0,864285714 Nature Works Ingeo 6202D 200 °C 30 °C 500 bar 0,258 0,294 0,87755102 Zhejiang Hisun Revode 190 200 °C 30 °C 500 bar 0,265 0,304 0,871710526 Jelu WPC Bio PLA H60-500-14 200 °C 30 °C 500 bar 0,154 0,171 0,900584795 Jelu WPC Bio PE H50-500-20 #DIV/0! FKuR Terralene HD 3505 230 °C 30 °C 500 bar 1,906 1,45 1,314482759 Evonik Vestamid Terra HS16 250 °C 80 °C 500 bar 1,558 1,631 0,955242183 Showa Denko Bionolle 1020MD 200 °C 30 °C 500 bar 0,814 0,839 0,970202622 Metabolix Mirel P1004 180 °C 30 °C 500 bar 0,404 0,64 0,63125 During processing, the bioplastic is melted in the injection moulding machine and injected under high pressure into an injection mold cavity. Once the cooling time is completed, the cooled part is ejected from the cavity. At this point, important aspects that must be observed when changing from a conventional plastic to a bioplastic – this also applies when changing to a different petroleum-based plastic – are the different shrinkage and warpage characteristics of the substituting material. The material shrinkage allows significant statements to be made concerning the compatibility of the selected material with the existing cavity and whether component distortion must be expected. If the The results of this investigations show that most of the investigated bioplastics show an almost isotropic shrinkage and warpage (FD/CD) behavior with a little more shrinkage in CD than in FD and a ranking lower than 1. This is similar to most of the petroleum-based plastics and therefore an important aspect of substitutability. Furthermore, it can be seen that the PLA-based bioplastics show a low shrinkage. This corresponds to a typical behavior of unreinforced amorphous thermoplastics. The other bioplastics have significantly higher processing shrinkages. In the case of Vestamid Terra HS16, the shrinkage is very high but in a magnitude typical for PA. The bioplastic Bionolle 1020MD 14 bioplastics MAGAZINE [03/18] Vol. 13
Injection Moulding By: Marco Neudecker, Nuse Lack, Hans-Josef Endres Institute for Bioplastics and Biocomposites – IfBB University of Applied Sciences and Arts Hanover, Germany Figure 1: Shrinkage and warpage of bioplastics FD/CD Ranking 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 Nature Works Ingeo 3052D Nature Works Ingeo 3251D Nature Works Ingeo 6202D Zhejiang Hisun Revode 190 Jelu WPC Bio PLA H60-500-14 — — — — — — Jelu WPC Bio PE H50-500-20 not measurable due to bad surface — FKUR Terralene HD 3505 — Evonik Vestamid Terra HS16 — Showa Denko Bionolle 1020MD — Metabolix Mirel P1004 — FD/CD Flow Direction (%) Cross Direction (%) also shows increased shrinkage values which are still in the lower usual range of semi-crystalline thermoplastics. Significant anisotropy is exhibited by the Mirel P1004 and the Terralene HD 3505. The shrinkage of Mirel P1004 is characteristic of largely amorphous thermoplastics, which also have a relatively high viscosity. Striking is the high anisotropy, which makes this material prone to distortion. Terralene HD 3505 belongs to semi-crystalline thermoplastics but shows a very high shrinkage value, especially in FD. We STARCH your bioplastics. Made in Austria. The results listed here and many other conclusions relevant to processors could be identified in the processing project funded by the German Federal Ministry of Food and Agriculture. All results are freely accessible and available to anyone interested in two databases: • Material Data Center (www.materialdatacenter.com/bo/) • Project Results Database (http://www.biokunststoffeverarbeiten.de). The project outcome closes important gaps in the knowledge of the processing of bio-synthetic materials. For further questions the competence network of project partners can be contacted (http://verarbeitungsprojekt. ifbb-hannover.de/de/projektkontakte.html). www.ifbb-hannover.de AMITROPLAST ® THERMOPLASTIC STARCH BIOBASED. COMPOSTABLE. SUSTAINABLE. PERFORMING. COST COMPETITIVE. FOR YOU. AMITROPLAST ® allows you to incorporate 50 % or more of thermoplastic starch in your compound for film extrusion and injection moulding. AGRANA.COM bioplastics.starch@agrana.com THE NATURAL UPGRADE bioplastics MAGAZINE [03/18] Vol. 13 15
