Injection moulding Both
Injection moulding Both tests measured the force (compressive load) to break/bend a cutlery, and how much distance is compressed before the cutlery failed. The area under the curve of force vs. distance provided the toughness (energy absorbed at break) of each cutlery based on design and material performance. Cutlery made using Natur-Tec BF3002HT resin, was benchmarked against standard PS and PP cutlery sold in the market, for performance metrics such as mechanical strength, hot water resistance and warpage. The PS cutlery benchmarked was similar in weight and length as the Natur-Tec cutlery, whereas the PP cutlery was slightly smaller and lower in weight. Rigidity Performance Data: Figures 2(a) and (b) show results obtained from the Rigidity test. Figure 2(a) shows that both PS and PLA are rigid and stronger materials at room temperature and need a higher force to break/ deform as compared to the PP cutlery. Figure 2(a) also shows that PS is more brittle and breaks sooner, as compared to the PP or Natur-Tec cutlery. It is noteworthy that Natur-Tec’s modified Ingeo PLA cutlery did not break and withstood more of the applied force before deforming (about 2 kg force). PP cutlery also did not break but it deformed when the applied force was only) 0.5 kg. This is evident in figure 2(b), where toughness or total energy absorbed to break was compared. Natur-Tec cutlery exhibits higher toughness as compared to both PS and PP cutlery. Performance in Hot Water: Figure 3(a) and (b) show results obtained from a Hot Water test where force to deform a cutlery was measured at two temperatures: 80 °C and 90 °C. Any changes in shape after the force was applied were also noted. The PS cutlery was the most rigid cutlery at the lower temperature as shown in figure 3(a). At higher temperatures of 90°C, closer to the T g of PS, the PS cutlery begins to soften and consequently the force to deform it dropped significantly – figure 3(b). Also PS cutlery deformed after being compressed in hot water as shown in picture, while Natur-Tec’s (and the PP) cutlery retained its shape as they were still flexible. Warpage in Post-Annealing: Warpage of the cutlery during the post-annealing step tends to be a major issue that affects overall yield and therefore the per-piece cost. As a result, warpage of the molded cutlery was studied as a function of masterbatch amount used in Natur- Tec’s 2-part resin system. Warpage for the spoon was measured as changes in the length of the handle, and the width of the spoon bowl. The annealing conditions used were maintained the same for all parts in a convection oven. Figure 4 shows change in width of spoon-bowl. It was found that as the percentage of highly filled masterbatch was increased, the warpage of the cutlery decreased. Warpage plateaued out at approximately 2 % at a masterbatch loading level of 50 %. The crystallinity of all the cutlery samples tested was 40 – 50 %. Summary PLA is a semi-crystalline polymer with T g of 55 °C and therefore behaves as a glassy polymer at room temperature like PS, At However at use temperatures above 55 °C, PLA cutlery will deform and will not be usable. Developing crystallinity in PLA allows use of PLA upto 90 °C because the crystalline domains hold the structure together and prevent deformation. Crystallized PLA cutlery tends to be flexible like PP cutlery at higher Figure 2: (a) Stiffness comparison of spoon made with PS, PP and Natur-Tec’s modified Ingeo PLA; (b) Toughness comparison of spoon made with PS, PP and Natur-Tec’s modified Ingeo PLA Maximum compressive load, kg 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.0 (a) PS Natur-Tec modified Ingeo PP 0.2 0.4 0.6 0.8 1.0 1.2 Normalized distance at break Energy at break, N-mm 600 500 400 300 200 100 0 (b) PS PP Natur-Tec modified Ingeo Figure 3: Hot water performance of spoon made with PS, PP and Natur-Tec’s modified Ingeo PLA (a) at 80 °C and (b) at 90 °C Maximum compressive load, kg 16,000 14,000 12,000 1,000 800 600 400 200 0 (a) PS PP Natur-Tec modified Ingeo Maximum compressive load, kg 16,000 14,000 12,000 1,000 800 600 400 200 0 (b) PS PP Natur-Tec modified Ingeo PS PLA 18 bioplastics MAGAZINE [03/16] Vol. 11
temperatures. Crystallization can be carried out in two ways: (1) as in-mold annealing where part is crystallized in a heated mold at 100 – 130°C and (2) as post-annealing where part is molded with a cold mold and then crystallized in a second step in an oven. Cutlery made with Natur-Tec’s modified Ingeo PLA compound has better toughness than PS cutlery of the same weight. Warpage, in post-annealed cutlery, is significantly reduced as the masterbatch is increased from 15 % to 50 %. The 2-part Natur-Tec resin solution helps retain molecular weight, and provides better mechanical performance as compared to a traditional filled-PLA compound. Acknowledgements We would like to acknowledge the strong support of NatureWorks Llc, in particular, Nicole Whiteman for her technical expertise and guidance on Ingeo PLA PLA materials. References [1] “Processing And Properties Optimization Of Dynamic Injection-Molded PP”, Wu Hongwu Zhong Lei Qu Jinping National Engineering Research Center of Novel Equipment for Polymer Processing South China University of Technology, Guangzhou 510640, China, ANTEC 2005, pp 884 – 888. [2] “High Heat Performance Ingeo for Foodservice Ware”, Nicole Whiteman, NatureWorks Llc., Innovation Takes Root Conference 2014. [3] “The Importance of Melt & Mold Temperature”, Michael Sepe from Michael P. Sepe LLC, Plastics Technology, December 2011. [4] “Impact Of Crystallization On Performance Properties And Biodegradability Of Poly(Lactic Acid)”, Shawn Shi & Ramani Narayan, Michigan State University, East Lansing MI, ANTEC 2013 Ohio. [5] “Effects Of Annealing Time And Temperature On The Crystallinity And Dynamic Mechanical Behavior Of Injection Molded Polylactic Acid (PLA)”, Yottha Srithep, Paul Nealey and Lih-Sheng Turng, University of Wisconsin– Madison, Madison, WI, Polymer Engineering & Science, Volume 53, Issue 3, pages 580–588, March 2013. [6] Military Spec: http://everyspec.com/COMML_ITEM_DESC/A-A-03000_A-A- 03999/A-A-3109_41836/ Think Sustainable M·VERA ® – biodegradable bioplastic With our M·VERA® range of biodegradable plastics (certified to EN 13432), we provide you with customized solutions for your application: • Film Such as shopping bags, biowaste bags or agricultural films • Injection moulding Such as coffee capsules, cutlery, toys and others • Color, carbon black and additive masterbatches Our team of highly experienced plastic specialists is pleased to help you – contact us! Figure 4: Warpage of spoon as measured by decrease in width of spoon-cup for cutlery made with different levels of masterbatch blended with virgin Ingeo PLA 12.0 % Shrink in width of spoon 10.0 8.0 6.0 4.0 2.0 0.0 0 10 20 30 40 50 60 % Highly-filled masterbatch in Natur-Tec‘s modified compound BIO-FED Branch of AKRO-PLASTIC GmbH BioCampus Cologne · Nattermannallee 1 50829 Cologne · Germany Phone: +49 221 88 8894-00 Fax: +49 221 88 8894-99 info@bio-fed.com www.bio-fed.com bioplastics MAGAZINE [03/16] Vol. 11 19
