Fig. 6. Various degrees
Fig. 6. Various degrees of transparency of the panels and their thermal stability (HDT-B), depending on the formulation and production parameters of the material during the post-mould treatment should be considered during the mould design. The aim was to get a good HDT-B and a high degree of transparency. The yellowness index of the PLA was neutralized with an optical brightener for polylactide. Depending on the dosage of additives, the bioplastic compound consists of 92.5 % by wt. of renewable raw materials Outlook The necessary longer cycle time of 180 to 240 seconds, instead of about 20-30 seconds, reduces production capacity per day. This leads to a high cost per piece. This aspect leads to the conclusion that this PLA compound could be mainly used in the higher priced design sector. The further goal is to minimize the cycle time for each halfshell and to improve the transparency. www.itke.uni-stuttgart.de www.nimbus-group.com test compound processing and curing HDT-B [°C] t1 PLA (without additives) CT 25°C; cooling time regular 51,7 t2 PLA + nucleating agent CT 25°C; cooling time regular 51,9 CT 25°C; cooling time regular 45,6 CT 100°C; cooling time 3min 64,9 CT 100°C; cooling time 4min 65,3 PLA + TPP (8wt%) CT 25°C; cooling time regular; 73,5 t3 + nucleating agent (4wt%) temper 5min at 100°C + brightener CT 25°C; cooling time regular; 97,3 temper 180min at 100°C CT 100°C; cooling time 4min; 112,5 temper 480min at 100°C PLA + TPP (7wt%) CT 100°C; cooling time 3min 59,7 t4 + nucleating agent (3wt%) + brightener CT 100°C; cooling time 4min 79,9 cavitiy temperature (CT) parameter HDT-B: ramp: 120.00 °C/h start temperature: 26°C preheat time: 300s workload: 0.450 MPa Fig.5. HDT-B subject to processing method and curing 40 bioplastics MAGAZINE [02/12] Vol. 7
Additives By Michael Wagner Deifel Buntfarbenfabrik Schweinfurt, Germany Colour-differences of conventional HDPE to PLA, PLA blend and PBS, that were each pigmented with the same yellow, red, green and blue masterbatch, with the first column showing the natural colour of each plastic. In this colouring test the maximum pigment level allowed (regarding the heavy-metal content as per EN 13432), was used in order to show the optimum colouring effect. HDPE PLA Colorants for bioplastics PLA-Blend PBS Today many biobased and/or biodegradable/compostable plastics are required to be coloured. In order to fulfil, for instance, the compostability standards (such as EN 13432 or ASTM D6400), some specific technical know-how is essential with regard to pigment composition and the quantity required for a specific task. Whereas dispersing agents or other processing aids could be chosen on a natural basis (e.g. wax, oil, etc.), for pigments and other dyestuffs it is quite different: bio-based and biodegradable colorants of herbal origin (e.g. indigo) do not withstand the high processing temperature of thermo(bio-) plastics, hence no ecological alternatives for conventional colorants are available. Therefore a certain percentage of non-biodegradable components has to be tolerated: for instance according to EN 13432 a maximum of five different alien (i.e. non-biodegradable) components is allowed, with each not exceeding one percent in the end-product. Of course, besides quantity, the quality of colorants is also of decisive importance. Only pigments and other dyes, which are recommended for the colouring of bioplastics, should be used. A decisive restriction is, for instance, the heavy-metal content, which excludes a large number of colorants and limits both the possibilities of combination among themselves (affecting various colour-shades, created by pigment mixtures), and their percentage as an addition to the desired bioplastic (affecting the intensity of a colour). A potential negative influence on compostability, which may be caused by an unpredictable reaction between single components, will not be seen before the certification tests. This is one of the reasons why testing of the end-product is essential. However, a specific and safe previous choice of working materials (in this case the colorants) is reasonable and may be more likely ensure a successful certification to the norms mentioned above. Considering this, the company Deifel GmbH & Co. KG in Schweinfurt, Germany, has tested various bio-plastics and cooperated with appropriate test laboratories. Even faced with the stringent requirements in the standards, good prospects for colorants suitable for bio-compostable plastics have been developed. With the product line Dei ® Bio, the colorant producer Deifel designed colour batches, which are matched exactly to this special purpose. The pigment formulation and the masterbatch producer will competently and consultatively assist all customers in the plastics processing business, enabling them to realize their individual goals when it comes to product colour – whether bio-based or biodegradable/compostable. Besides prescriptive limits regarding heavy metal content, the basic and natural colour of a certain bioplastic plays a major role that has to be considered. The same colorant may look quite different within various plastics (see photo). Therefore, when choosing a suitable bioplastic, not only technical requirements, but also the limits of possible colours should be in focus. The transparent appearance of natural PLA allows a high degree of freedom when considering colours. However, if there are any technical requirements (e.g. shock-resistance achieved by using a PLA blend) it is usually necessary to compromise on the coloration, because of the restrictions outlined above. The colour applications laboratory at Deifel is engaged in this subject and can usually help with the choice of the appropriate type of bio-plastic. For most biodegradable/ compostable plastics (e.g. PLA, PBS, PHA, …) pigment powder or masterbatch pellets can be used for colouring. www.deifel-masterbatch.de bioplastics MAGAZINE [02/12] Vol. 7 41
