Biodegradable Polycaprolactone as a Mechanical Property Enhancer for Bioplastics

Abstract

This master thesis paper deals with the theory and development of bioplastic blends with polycaprolactone (PCL) as a mechanical property enhancer. Polylactic acid (PLA) was blended with PCL in concentrations ranging from 5 to 35%, the blends were prepared through melt extrusion in a co-rotating twin-screw extruder with the aim of improving the tensile and impact properties compared to pure PLA. The extruded blends were molded into test specimens by compression and injection molding followed by mechanical testing. The testing included tensile, impact, softening temperature, melt flow rate and rheology. The degradation during extrusion was also examined through gel permeation chromatography (GPC), and it was found that no significant degradation took place during processing.
Two different grades of PCL were used; one of high molecular weight (Capa™6800) and one of lower molecular weight (Capa™6500). The Capa™6500 compounds showed a significant toughening effect at a concentration of 35% while the Capa™6800 only showed a toughening effect at elevated temperatures. Both Capa™ grades give a big increase in strain at break compared to the pure PLA. The morphology of the materials is not known but is most likely the source of the difference in properties between the two compounds and further tests and analysis would be helpful in deciphering the behavior of these blends. PCL was not found to have an obvious detrimental effect on the softening temperature at the tested component ratios, but this needs to be confirmed by further testing of PCL blends.

Abstract (Swedish)

Detta examensarbete behandlar teorin kring samt utvecklingen av biologiskt nedbrytbara polymerblandningar med polykaprolakton (PCL) som en av komponenterna. PLA (Polylactic acid, en mjölksyrapolymer) blandades med PCL i koncentrationen 5 till 35% och blandningarna framställes genom extrudering i en dubbelskruvsextruder i syfte att förbättra drag- och slagegenskaper jämfört med ren PLA. De extruderade blandningarna formades till provbitar genom pressning och formsprutning, följt av mekanisk testning. Testningen innefattade dragprovning, slagprovning, mätning av mjukningstemperatur, smältindex och reologi. Nedbrytningen under extrudering undersöktes också genom gelpermeationskromatografi (GPC), och resultaten från denna visade att ingen signifikant nedbrytning ägde rum under bearbetningen. Två olika kvaliteter av PCL användes; en av hög molekylvikt (Capa™6800) och ett med lägre molekylvikt (Capa™6500). Blandningarna med Capa™6500 visade en signifikant ökning i seghet vid en koncentration av 35% medan Capa™6800 endast gav en seghetseffekt vid förhöjda temperaturer. Båda Capa™-kvalitéerna ger en stor ökning av brottöjning jämfört med den rena PLA. Morfologin av materialen är inte känd men är troligen orsaken till skillnaden i egenskaper mellan de två föreningarna, ytterligare tester och analyser behövs för att reda ut källan till beteendet hos dessa polymerblandningar. Det kunde konstateras att PCL inte hade någon tydlig negativ effekt på mjukningstemperatur vid de testade förhållandena, men på grund av mycket små skillnader i mjukningstemperatur hos de ingående komponenterna måste detta bekräftas av ytterligare tester.

Popular Abstract

In 2014 the consumption of plastics reached 300 million tons only in Europe and about 7% of these materials was recycled. Only a very small fraction are made from renewable plastics and an even smaller part is biodegradable, this means that huge amounts of non-biodegradable plastic waste ends up in our environment, whether it is as litter in nature, in landfills or as carbon dioxide from energy recovery plants. One big problem with these non-degradable plastics is that sooner or later they will end up in the oceans where they will partly decompose into microscopic fragments and follow the sea currents and thus accumulate in big “islands” of plastic sludge that can cause harm to the ecosystems and aquatic wildlife. Introducing renewable and biodegradable plastics could be a solution to this problem. Biodegradable plastics will decompose in the presence of microbes that are naturally occurring in the environment, but there are still some obstacles in introducing these plastics to the market. The mechanical properties are often a challenge and to make these materials a viable option, their performance has to be comparable with that of the conventional plastics. PLA (Polylactic acid) is a fully renewable and biodegradable material that has some mechanical property limitations; it is brittle and breaks even from small deformations. One way of enhancing the properties of plastic materials is to mix (blend) it with a plastic that have more desirable properties. This method is commonly known as polymer blending and is widely used to improve materials and tailor-make materials to suit different applications. For PLA it would thus be desirable to blend with a substance with good ductility and
toughness without compromising the biodegradability of the material, and polycaprolactone (PCL) meets these requirements.

By blending PLA with PCL the aim is to get the best properties from both materials and create a product with superior performance than the components in their pure form. The PCL is non-renewable and also the more expensive component in the blend, hence, the amount of PCL that is added to the PLA should not exceed 35%.

In this master thesis the effects of the blending of these plastics is tested and evaluated, and the results are promising. The PCL seems to be highly compatible with the PLA, which means a good mixing is easily
achieved with great improvements in the mechanical properties as a result. Some of the biggest performance limitations for PLA were improved (e.g. elongation at break and impact toughness). Some additional work needs to be done to verify and explain the origin of these results, but with studies like this one, plastics manufacturers like Perstorp can create arguments for expanding the use of bioplastics to large volume markets such as the food packaging industry, which hopefully can contribute to a more sustainable society.

• author: Rydén, Emelie
• supervisor: Matilda Larsson; Linda Zellner; Dzina Kleshchanok
• organization: Centre for Analysis and Synthesis
• course: KTE720 20151
• year: 2016
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: biodegradable, extrusion bioplastics, polymer blend, polycaprolactone, PCL, polylactic acid, polymer, PLA, biocompatible, mechanical properties, polymerteknologi, polymer technology
• language: English
• id: 8520637
• date added to LUP: 2016-02-01 16:53:28
• date last changed: 2016-02-01 16:53:28