Evaluation of Polylactic Acid (PLA)

Transcription

1 Evaluation of Polylactic Acid (PLA) This document provides information obtained from research into polylactic acid (PLA) as a substitute material for various other plastics used as disposable cup lids. First the background of PLA and its synthesis is explained, followed by a summary of material comparison data to other plastics and finally, an evaluation on the feasibility of using composting facilities in Ireland to decompose PLA. Background PLA is a biodegradable aliphatic polyester that is an equivalent to many modern thermoplastics. PLA is produced from lactic acid, an organic compound which can be derived from various extraction and fermentation processes of 100% natural and renewable resources such as corn starch and sugarcane. Lactic acid can also be directly synthesised through various chemical processes, however lactic acid for PLA is nearly always derived from extraction and fermentation [1]. There are two main routes by which PLA can be synthesised in modern times: lactic acid itself is directly condensed at high temperatures to form a new mixture, which is then converted to PLA by catalysis, or else the lactic acid can first be converted to a small polymer known as lactide before further conversion to PLA. Most of the world s PLA in current times is produced through the formation and upgrading of lactide [1]. Physical Properties PLA is designed to be a renewable alternative to other plastics such as polyethylene (PE) and polyethylene terephthalate (PET). In order to evaluate PLA as an alternative to these plastics, research was conducted into its various mechanical and material characteristics. A study carried out in 2004 by ASTM International, an international standards organisation, evaluated the performance of PLA against existing plastics as various forms of food packaging/containers. PET and polystyrene (PS) were selected as benchmark materials, which are extensively used to package fresh food and disposable containers/lids. It was found that treatment of PLA, PET and PS with weak and strong acids for seven days did not affect their structural integrity. In terms of impact resistance, PET was most resistant followed by PLA and PS. The study concluded that proprieties of PLA relevant to packaging applications are rather similar to PET and PS, suggesting a wide range of uses for PLA in the industry [2]. From this

2 research, it was decided by the team that many of the biodegradable takeaway cup lids would be ideal candidates from a functionality perspective. Composting of PLA The team was aware that for PLA to be a viable alternative to other plastics, it must be easily composted, and the facilities to carry out this process must exist within Ireland s waste processing industry. This evaluation required research into two distinct areas: the technical process behind PLA composting, and the composting industry in Ireland. Technical Aspects Initial research through google searches leaves details on the composting of PLA rather vague. Many people in the public express concerns and difficulties when attempting to compost PLA at home with their usual municipal wastes; this is evident through numerous blog posts, forum discussion and website articles. Research in academic literature provides much more definitive answers to the simple question: what conditions are necessary for effective PLA composting?. Two very interesting scientific studies that explored this question were found by team. These are summarised as follows: 1) A study carried out in 2001 by Ghorpade et al. [3] examined the composting of extruded PLA sheets with pre-composted yard/garden waste in a laboratory scale setting. The term precomposted refers to wastes which had previously been composted for 7 months (i.e. a typical ongoing compost heap). Different amounts of PLA were added to set amounts of precomposted yard/garden wastes and the decomposition of the PLA was evaluated based on simple observation and the measurement of released carbon dioxide and the mixture s ph. They concluded that the maximum amount of PLA that should be added to the pre-composted waste should not exceed 30% of the mixture s final weight. Higher amounts of PLA inhibited composting due to overconcentration of components that inhibited microbial growth and chemical hydrolysis [3]. 2) The degradation of PLA in both Costa Rican soil and laboratory composting rows was evaluated by Ho et. al [4]. At the time of writing, 1999, Costa Rica had used 200 metric tons of PE ropes each year for banana production; with these ropes being discarded into fields leaving a large accumulation of plastic in the environment. The basis of this research was to examine

3 the degradation of PLA in Costa Rican soil to determine whether or not PLA could be used as an alternative plastic in the banana industry. PLA films were added to soil in Costa Rican fields similar to those where PE was being discarded. The same type of PLA films were also added to two laboratory composting rows in Iowa State University; these rows maintained a temperature of 55-60C and a humidity rating of 50-70% throughout the study. It was found that the PLA required 2 weeks to begin physical disintegration in the laboratory, after 3 weeks the PLA was visibly disintegrated. In the Costa Rican fields, it was found that the degradation of PLA did not impact the overall soil ph; this was important as there were initial concerns of negative impact on soil. Furthermore, degradation rates for some PLA polymers were comparable to the laboratory composting tests. Overall, due to fluctuations in weather conditions it was estimated that it would take approximately 6 months for PLA to visible degraded in unmaintained soil [4]. These studies show that it is indeed possible to easily compost PLA under the correct conditions. However as could be seen in the Costa Rican soil experiment, less controlled conditions can lead to much longer degradation times; this was similar to what was found through personal accounts of composting difficulties from various blogs/forums/website articles. It was concluded by the team that while effective composting of PLA is indeed possible, it would require an industrial/professional facility to be confidently processed, thus evaluation of the Irish commercial composting industry was required. Composting in Ireland The most authoritative and recent statistics on commercial composting and anaerobic digestion facilities in Ireland were published by the Environmental Protection Agency (EPA) in May 2016, based on major studies carried out throughout Three documents were published: a main summary [5], a classification/breakdown of composted materials [6] and a list of industrial composting facilities within Ireland [7]. It was found that in 2015, the amount of waste accepted to these facilities was approximately 300 kilotons (kt); this was an increase of 11% from studies carried out in There were 36 different commercial facilities listed, whose capacities varied between 60 and 96,000 tons per annum [6] ; approximately two thirds of these facilities carried out major composting activity while the others specialised in anaerobic digestion. Composting however was the predominant method of material treatment, accounting for the processing >80% of all accepted material [5].

4 Regarding the classification of accepted materials, municipal wastes (such as food waste, waste and plant material) were the most abundant, accounting for 65% of all waste treated; furthermore, a vast majority of these wastes came from residential and commercial organic/brown bins. Sludges from waste water treatment plants and wastes from beverage production were other dominant sources, representing 15% and 8% of the total accepted waste respectively [5],[6]. These statistics are summarised in Figure 1, a chart taken from the EPA s main summary. Figure 1: Classification of waste materials (total weight approx. 300kt) accepted for treatment in commercial composting and anaerobic digestion facilities in Ireland during 2015 (Taken from the EPA s main summary [5] ). Overall, the composting industry in Ireland is growing and is quite diverse; however, there was still not much indication on the acceptance or role of PLA in these processes. The material classification document provided by the EPA did not specifically mention bioplastics or related materials, the only classification which seemed linked to our research was termed Packaging, which represented 317 tons of waste material. The team decided to research these classifications further, which lead to the discovery of another document published by the EPA in 2015, a guidebook to all of their official waste classifications [8]. From this document, it was found that the classification of Packaging was used to described nearly all kinds of packaging including paper, cardboard, plastic, metals, textiles and composites. There was no further breakdown in these descriptions and no reporting on exactly which of these contributed to packaging processed by the composting facilities. Following this, the team decided the best course of action would be to research guidelines put forward by waste collection businesses on what materials are accepted for composting from the customer s (both residential and businesses) organic/brown bin. The team reviewed documentation

5 from four major waste collection companies in Ireland: Panda Waste Management [9], Mr.Binman [10], Clean Ireland Recycling [11] and AES [12]. Upon review, it was found that all four companies did not want any plastics to be added to their bin, requesting mainly food waste, paper, carboard and plant materials [10],[11],[12],[13]. Furthermore, BrownBin.ie, a website launched by the Composting & Anaerobic Digestion Association of Ireland and the Department of Environment, Community & Local Government also states not to place any kinds of plastic materials in organic/brown bins; making no mentions of bioplastics [13]. All of this information lead the team to decide that PLA would likely not be accepted by these facilities and thus end up in landfill, which eliminated it as a replacement material. Conclusions Review of PLA showed that it was a very promising alternative material with a wide array of applications. Many companies have already taken to manufacturing PLA as an alternative material for disposable coffee cup lids. However, investigation of the technical aspects of PLA composting showed that while it is indeed compostable to various international standards, it requires very specific conditions to be efficiently degraded (times of 3-4 weeks were achievable in very controlled studies, whereas this spanned to months in less controlled efforts). Finally, investigation of the composting industry in Ireland revealed that in 2015, approximately 317 kilotons of material was processed by composting and anaerobic digestion plants; 300 tons of which were classified as packaging. Further investigation however revealed that this did not include bioplastics and 4 major waste collection companies did not accept any plastic for their residential and business collection services and guidelines set out by national associations/departments also highlighted that these should not be added. Due to all of this information, it was decided that PLA would not be a viable alternative material for our concept.

6 LIST OF REFERENCES 1.Drumright, R., Gruber, P. & Henton, D. Polylactic Acid Technology. Advanced Materials 12, (2000). 2.Auras, R., Singh, S. & Singh, J. Performance Evaluation of PLA against Existing PET and PS Containers. Journal of Testing and Evaluation 34, (2006). 3.Ghorpade, V. Laboratory composting of extruded poly(lactic acid) sheets. Bioresource Technology 76, (2001). 4.Ho, K., Pometto III, A., Gadea-Rivas, A., Briceño, J. & Rojas, A. Journal of Polymers and the Environment 7, (1999). 5.Composting and Anaerobic Digestion in Ireland in (2016). at < df> 6.Waste types accepted in (2016). at < 7.Facilities surveyed for 2015 data including site capacity information. (2016). at < d_maximumannualintake_2015.xlsx> 8.EPA Waste Classification. (2015). at < 5_Web.pdf> 9.What can I put in my bin?. Panda.ie (2017). at < 10.Mr.Binman General Guide on Compostable Waste. (2017). at < 11.Clean Ireland Recycling : Skip Hire and Waste Collection Services. Cleanireland.ie (2017). at < 12.Organic Waste - What Goes in My Bin?. AES (2017). at < 13.Welcome to Brownbin.ie Brownbin.ie. Brownbin.ie (2017). at <