Susan Selke

Poly(lactic acid) : synthesis, structures, properties, processing, and applications

This book describes the synthesis, properties, and processing methods of poly(lactic acid) (PLA), an important family of degradable plastics. As the need for environmentally-friendly packaging materials increases, consumers and companies are in search for new materials that are largely produced from renewable resources, and are recyclable. To that end, an overall theme of the book is the biodegradability, recycling, and sustainability benefits of PLA. The chapters, from a base of international expert contributors, describe specific processing methods, spectroscopy techniques for PLA analysis, and and applications in medical items, packaging, and environmental use.

Mechanical, Physical, and Barrier Properties of Poly(Lactide) Films

High molecular mass poly(lactide), (PLA), is an attractive polymer family because in addition to being thermoplastic, biodegradable, compostable, and produced from annually renewable resources, it shows mechanical and barrier behavior comparable to synthetic polymers like polystyrene (PS) and polyethylene terephthalate (PET). Furthermore, technology for large-scale fabrication of PLA has been fully developed. However, there is still a need to better understand the properties of PLA as this polymer is adapted to packaging applications, especially for food packaging. In this work, films from two PLA resins were studied by tensile testing; differential scanning calorimetry (DSC); and permeation of carbon dioxide, oxygen, and water vapor. The data from these two PLA film samples are compared to those of PS and PET.

Active Packaging of Fresh Chicken Breast, with Allyl Isothiocyanate (AITC) in Combination with Modified Atmosphere Packaging (MAP) to Control the Growth of Pathogens

Listeria monocytogenes and Salmonella typhimurium are major bacterial pathogens associated with poultry products. Ally isothiocyanate (AITC), a natural antimicrobial compound, is reportedly effective against these pathogenic organisms. A device was designed for the controlled release of AITC with modified atmosphere packaging (MAP), and then evaluated for its ability to control the growth of L. monocytogenes and S. typhimurium on raw chicken breast during refrigerated storage. In order to obtain controlled release during the test period, a glass vial was filled with AITC and triglyceride. It was then sealed using high-density polyethylene film. The release of AITC was controlled by the concentration (mole fraction) of AITC in the triglyceride and by the AITC vapor permeability through the film. The fresh chicken samples were inoculated with one or the other of the pathogens at 10(4) CFU/g, and the packages (with and without AITC-controlled release device) were flushed with ambient air or 30% CO(2)/70% N(2) before sealing, and then stored at 4 degrees C for up to 21 d. The maximum reduction in MAP plus AITC (compared to MAP alone) was 0.77 log CFU/g for L. monocytogenes and 1.3 log CFU/g for S. typhimurium. The color of the chicken breast meat was affected by the concentration of AITC. Overall, a release rate of 0.6 microg/h of AITC was found to not affect the color, whereas at 1.2 microg/h of AITC the surface of the chicken was discolored.

Packaging: Papers for Sacks and Bags

This work examines wood fiber-based paper materials that are widely used throughout the world in packaging applications. Two of the advantages of using wood fiber based paper are in their strength and cost. They are natural, recyclable, biodegradable, and versatile materials backed by a dynamic and innovative paper industry. As a result of their biodegradability, its impact on environment as compared with plastic bags is very friendly. The recommended specification for normal moisture content of paper on a dry weight basis is 5%±2% and the paper materials must be tested at standard conditions of 23±2°C and 50%±2% RH, according to ASTM D 685 and TAPPI standard T402.

Life Cycle Assessment Software: Selection Can Impact Results

When software is used to facilitate life cycle assessments (LCAs), the implicit assumption is that the results obtained are not a function of the choice of software used. LCAs were done in both SimaPro and GaBi for simplified systems of creation and disposal of 1 kilogram each of four basic materials (aluminum, corrugated board, glass, and polyethylene terephthalate) to determine whether there were significant differences in the results. Data files and impact assessment methodologies (Impact 2002, ReCiPe, and TRACI 2) were ostensibly identical (although there were minor variations in the available ReCiPe version between the programs that were investigated). Differences in reported impacts of greater than 20% for at least one of the four materials were found for 9 of the 15 categories in Impact 2002+, 7 of the 18 categories in ReCiPe, and four of the nine categories in TRACI. In some cases, these differences resulted in changes in the relative rankings of the four materials. The causes of the differences for 14 combinations of materials and impact categories were examined by tracing the results back to the life cycle inventory data and the characterization factors in the life cycle impact assessment (LCIA) methods. In all cases examined, a difference in the characterization factors used by the two programs was the cause of the differing results. As a result, when these software programs are used to inform choices, the result can be different conclusions about relative environmental preference that are functions purely of the software implementation of LCIA methods, rather than of the underlying data.

Evaluation of Biodegradation-Promoting Additives for Plastics

Biodegradation-promoting additives for polymers are increasingly being used around the world with the claim that they effectively render commercial polymers biodegradable. However, there is a lot of uncertainty about their effectiveness in degrading polymers in different environments. In this study, we evaluated the effect of biodegradation-promoting additives on the biodegradation of polyethylene (PE) and polyethylene terephthalate (PET). Biodegradation was evaluated in compost, anaerobic digestion, and soil burial environments. None of the five different additives tested significantly increased biodegradation in any of these environments. Thus, no evidence was found that these additives promote and/or enhance biodegradation of PE or PET polymers. So, anaerobic and aerobic biodegradation are not recommended as feasible disposal routes for nonbiodegradable plastics containing any of the five tested biodegradation-promoting additives.

Assessment of the properties of poly(L-lactic acid) sheets produced with differing amounts of postconsumer recycled poly(L-lactic acid)

The properties of sheet containing mechanically recycled postconsumer poly(L-lactic acid) bottle flakes blended with virgin poly(L-lactic acid) resin were assessed. Poly(L-lactic acid) bottles were flaked, cleaned, blended with virgin resin and then extruded and thermoformed into trays. The molecular weight, physical, optical, thermal and mechanical properties of the sheet containing 0, 20, 40, 60, 80 and 100 wt.% poly(L-lactic acid) recycled content were evaluated. The best cleaning conditions were found by using a mixed-level fractional factorial design. Cleaning conditions of 15 min, at 85°C, 1 wt.% NaOH and 0.3 wt.% surfactant were adopted for cleaning the poly(L-lactic acid) flakes. Cast-extruded virgin poly(L-lactic acid) sheet had superior mechanical and optical properties than recycled poly(L-lactic acid) sheet. Recycled poly(L-lactic acid) sheets were darker and absorbed more ultraviolet light in the 260 to 285 nm range when 20% or more recycled content was added. At 40% poly(L-lactic acid) recycled content, the sheet had increased blue and red tones and the mechanical properties in the cross-machine direction decreased. At 60% poly(L-lactic acid) recycled content or above, reduction of weight average molecular weight, tensile strength and tensile strength at yield in the machine direction were found. At 80% poly(L-lactic acid) recycled content, the melting temperature and modulus of elasticity in the machine direction decreased. All sheet samples were successfully thermoformed into trays showing the potential to use post-consumer poly(L-lactic acid) flakes in the production of poly(L-lactic acid) containers.

Impact of Nanoclays on the Biodegradation of Poly(Lactic Acid) Nanocomposites

Poly(lactic acid) (PLA), a well-known biodegradable and compostable polymer, was used in this study as a model system to determine if the addition of nanoclays affects its biodegradation in simulated composting conditions and whether the nanoclays impact the microbial population in a compost environment. Three different nanoclays were studied due to their different surface characteristics but similar chemistry: organo-modified montmorillonite (OMMT), Halloysite nanotubes (HNT), and Laponite® RD (LRD). Additionally, the organo-modifier of MMT, methyl, tallow, bis-2-hydroxyethyl, quaternary ammonium (QAC), was studied. PLA and PLA bio-nanocomposite (BNC) films were produced, characterized, and used for biodegradation evaluation with an in-house built direct measurement respirometer (DMR) following the analysis of evolved CO2 approach. A biofilm formation essay and scanning electron microscopy were used to evaluate microbial attachment on the surface of PLA and BNCs. The results obtained from four different biodegradation tests with PLA and its BNCs showed a significantly higher mineralization of the films containing nanoclay in comparison to the pristine PLA during the first three to four weeks of testing, mainly attributed to the reduction in the PLA lag time. The effect of the nanoclays on the initial molecular weight during processing played a crucial role in the evolution of CO2. PLA-LRD5 had the greatest microbial attachment on the surface as confirmed by the biofilm test and the SEM micrographs, while PLA-QAC0.4 had the lowest biofilm formation that may be attributed to the inhibitory effect also found during the biodegradation test when the QAC was tested by itself.

Life cycle inventory data quality issues for bioplastics feedstocks

PurposeBioplastics are a growing field, but with their expansion come unique environmental issues associated with the cultivation and processing of feedstocks. Availability of appropriate, high-quality data is a problem in life cycle assessment (LCA) of biopolymers and other bio-based materials that limits the accuracy and usefulness of study results. It is therefore critical that these data gaps be closed. To determine what data is needed to close these gaps, this study reviews currently available life cycle inventory data for biopolymer feedstocks and assesses the data quality for the selected feedstocks of corn, sugarcane, and soy.MethodsLife cycle inventory databases and relevant publications were searched for appropriate data, and the results collected into a summary table. The quality review was conducted using a pedigree matrix type scoring system which was adapted from the ILCD handbook, and an overall quality score for each dataset was calculated based on the matrix scores.ResultsA total of 287 datasets were collected during the review for a total of 22 different feedstocks. The majority of these datasets are from Europe and the USA, with most of Asia, the Middle East, and Africa having very limited data available.ConclusionsFrom the quality analysis, it was determined that more datasets that capture regional variations in crop cultivation are needed, as well as more data on land use change.

Migration of antioxidants from polylactic acid films: A parameter estimation approach and an overview of the current mass transfer models

Migration studies of chemicals from contact materials have been widely conducted due to their importance in determining the safety and shelf life of a food product in their packages. The US Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA) require this safety assessment for food contact materials. So, migration experiments are theoretically designed and experimentally conducted to obtain data that can be used to assess the kinetics of chemical release. In this work, a parameter estimation approach was used to review and to determine the mass transfer partition and diffusion coefficients governing the migration process of eight antioxidants from poly(lactic acid), PLA, based films into water/ethanol solutions at temperatures between 20 and 50°C. Scaled sensitivity coefficients were calculated to assess simultaneously estimation of a number of mass transfer parameters. An optimal experimental design approach was performed to show the importance of properly designing a migration experiment. Additional parameters also provide better insights on migration of the antioxidants. For example, the partition coefficients could be better estimated using data from the early part of the experiment instead at the end. Experiments could be conducted for shorter periods of time saving time and resources. Diffusion coefficients of the eight antioxidants from PLA films were between 0.2 and 19×10-14m2/s at ~40°C. The use of parameter estimation approach provided additional and useful insights about the migration of antioxidants from PLA films.