Current state and future prospects of sensors for evaluating polymer biodegradability and sensors made from biodegradable polymers: A review

Management of municipal solid waste is a serious problem in the current world. Synthetic plastics have been used for various purposes, and annual production of the plastics in 2001 reached about 15 million tons in Japan, and 177 million tons in the world. However, synthetic plastics with high performance and stability cause serious problems in waste management. To solve the problem of plastic waste, biodegradable plastics have attracted the special attention of the public as the plastics of the 21st century, since they are biologically degradable and environmentally friendly. However, before the use of biodegradable plastics spreads, it is crucial to establish the test methods for their biodegradation in the environment. The Biodegradable Plastics Society1,2 has conducted two field experiments for estimating the degradation of biodegradable plastics in soil at more than 20 locations (including one location in the U.S.) over a period of 3 years. The results showed that all of the tested plastics were degraded in soil. Hoshino3 et al. reported on the influence of weather conditions, and soil properties for the degradation of biodegradable polymers. Nishide4 et al. reported that the degradation of biodegradable polymers occurred under aerobic conditions as compared to anaerobic conditions. Many studies on the degradation behaviour in aquatic and terrestrial environments were reported and several standard test methods were established in 2000 in the world, such as JIS K69505 (ISO 14851) and JIS K69516 (ISO 14852), relevant to aquatic environments and JIS K69537 (ISO 14855) for controlled composting condition, respectively. Especially JIS K6953 based on ISO 14855 is an excellent test-method, which automatically calibrates the evolved carbon dioxide by gas chromatography although it is yet presenting some difficulties. First, the reactor is suitable for large-scale tests and the apparatus is expensive. Second, it costs a great deal to examine specimens to develop biodegradable polymers, compounds and manufactured goods. The focus of this study is to develop the evaluating and screening test method for the biodegradation of plastic materials with a simplified apparatus on a laboratory scale.

In many regions, residential wood heaters are a leading source of harmful air pollution but only satisfy a small portion of local heating demands. In response, standardized laboratory test methods have been developed to characterize and limit wood heater emissions. While these test methods are a key tool for advancing both wood heater technology and environmental regulations, many of the experimental procedures are outdated and provide few actionable insights for improving heater performance. Furthermore, these test methods vary widely around the world and may not adequately capture the performance of wood heaters operating in residences. This study presents a comprehensive review of standardized wood heater test methods to identify fundamental experimental objectives and regulated performance metrics. Using the results of this review, recommendations are provided to make the test methods more accessible and representative of residential performance, while generating actionable data to motivate heater design improvements. This study elucidates the current state of standard test methods, and the developments needed to advance clean wood heater technologies and public policies.

14 - Standard test methods and their need to evolve

Introduction Cycle life test methods for batteries used in electric vehicles (EVs) have been proposed by several organizations, e.g., the International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC), and the Society of Automotive Engineers (SAE). In China, national industry standards (QC/T) including standards covering the test procedure for evaluating cycle life of batteries used in EVs have been established. However, there are few published results concerning evaluations of battery life using these standard test methods, and their adequacy remains uncertain. In this study, three types of cycle life tests were applied to high-capacity lithium-ion cells at 45°C. The degradation phenomena caused by each test method were evaluated, and their features and issues were considered. Experimental A commercial 40Ah class lithium-ion cell composed of a LiFePO4cathode and a graphite anode was used in this study. The cycle life of the cell was evaluated by three types of standard test methods, IEC62660-1 [1] and two types of QC/T (constant current and dynamic current profile, denoted as QC/T-1 and QC/T-2, respectively) at 45°C. The IEC 62660-1 cycle life test has two power-controlled dynamic discharge profiles: dynamic discharge profiles A and B shown in Figs. 1(a) and 1(b), respectively. In these profiles, the cell energy (Wh (at 25°C)) × 3 (1/h) was used as the maximum power. After fully charging at 1/3C in constant current-constant voltage (CC–CV) mode, the cell was discharged following the dynamic discharge profile A until the discharge capacity reached 50% ± 5% of the initial value. After the dynamic discharge profile B was applied once, the dynamic discharge profile A was reapplied until the discharge capacity reached 80% of the initial value. Then, the cell was discharged at 1/3C to the lower voltage limit. These procedures were repeated for 28 days. The cell performance, capacity (1/3 C), and internal resistance (DC) were periodically measured at 25°C. In QC/T-1, the cell was discharged at a constant current of 1 C to the lower voltage limit after fully charging. The cell performance was evaluated every 100 cycles. The procedure for QC/T-2 was somewhat more complex. The cell was discharged following the dynamic current profile (Fig. 2) until the state of charge (SOC) reached 20% and then charged at 1/3C in CC-CV mode to the upper voltage limit. This procedure was repeated four times; the expended time was defined as x h. Then, the cell was stored for 24 − x h at 100% SOC. The value of x depends on cell specifications; in this study, x was approximately 4 h. The entire procedure described above was repeated. The cell performance was evaluated at monthly intervals following IEC standards. Results and discussion The cycle life test was conducted for approximately 6 months, and the capacity retention results for three types of standard cycle life tests were compared. Three cells were evaluated by all three standard methods; average results are shown in Fig. 3. Cumulative discharge capacity was used as the horizontal axis to compare the results obtained from different cycle conditions. An equivalent cycle number, which was defined as the ratio of cumulative discharge capacity to the initial capacity, was added to the second horizontal axis to indicate cycle number. Rapid capacity decay was observed for QC/T-1 compared to IEC 62660-1 and QC/T-2. Similar results were obtained for internal resistance. Even though the maximum value of the C-rate in QC/T-1 is lower than other methods, the average was highest (Table 1). A high C-rate condition is thought to induce increased cell temperature and deformation of the crystal structure of electrode active materials. These phenomena can cause rapid degradation in QC/T-1. From the perspective of SOC, QC/T-2 has longer duration under high SOC conditions; however, capacity decay in QC/T-2 was not severe compared to other methods. The cathode potential of the cell used in this study is lower than other types of cathode materials, e.g., spinel-type lithium manganate or layered transition metal oxides. The low cathode potential is thought to weaken the impact on degradation under high SOC conditions. Other types of lithium-ion batteries have also been evaluated, and the results will be reported at the conference.

Construction aggregates are essential structural components in road structures, whether in unbound form or combined with cement or bitumen. Specifications and test methods for aggregates are standardised, but current standards are limited concerning the maximal aggregate size for which they apply. This paper deals with standard specifications and test methods for large-size road construction aggregates, reviewing a new Norwegian national standard for large-size aggregates. The standard test methods and their validity and applicability for use on large-size aggregates for road construction are evaluated. The differentiation between requirements regarding the rock material (single rocks) and the aggregate product is specifically discussed, as is the specific challenges related to the use of all-in aggregates. Current standards for construction aggregates do not cover all challenges related to description and quality assessment of construction aggregates. Quality assessment is particularly challenging for large-size aggregates, and this topic needs a better description by international standards. Field methods and digital image processing are introduced as solutions for some of the practical challenges related to sampling for large-size aggregates. The new Norwegian standard could be the first step towards a European standard for large-size aggregates.

Comparison of standard test methods for non-lubricated sliding wear

Acoustical properties of nonwoven fabrics are measured using several different test methods. These important test methods measure physical, mechanical and acoustic properties, which are important for the evaluation, characterization and differentiation of nonwoven fabrics for acoustical applications. Even the basic physical properties of nonwovens play a very important role in acoustics. Physical, mechanical and acoustical properties of nonwoven fabrics are measured using several standards that are defined in ASTM, ISO, ANSI and SAE test standards. Some other measurement techniques that are not included in any standard test methods can also be found in literature. In this chapter, important standard or nonstandard test methods related to acoustical properties of nonwoven fabrics are explained and described. Important physical properties of nonwoven fabrics for acoustical applications are areal density (mass), volumetric density, porosity, particle size distribution, tortuosity and thickness. Density parameters are the most important parameters for the differentiation of the nonwoven fabrics. Porosity also plays a major role in acoustical properties because each pore in the fabric becomes an absorptive material for the sound waves during sound wave–nonwoven fabric interaction. Mechanical parameters that are related to acoustical properties of nonwoven fabric are tensile properties and Young’s modulus. Acoustical absorption properties of nonwoven fabrics are determined using sound absorption coefficient, sound transmission loss, noise reduction coefficient, sound impedance and airflow resistivity parameters. These parameters could be measured using many different test methods. These methods are explained and related ASTM, ISO, ANSI and SAE test standards are discussed in this chapter. Especially impedance tubes and reverberation rooms are used for most of the acoustical test methods discussed in this chapter.

Tensile, impact, and creep properties of materials are evaluated using standard test methods following ISO, ASTM, and other international testing standards. These testing methods use large specimens and are material-intensive. Three innovative small specimen testing methods, namely impression creep (IC), small punch creep (SPC), and ball indentation (BI), are discussed that can be used to determine the mechanical properties of materials. IC is used to study the creep deformation behaviour of materials. SPC is used to evaluate creep deformation and fracture properties of materials. Tensile and hardness properties and fracture toughness can be evaluated using BI method. Unlike in conventional testing methods, all these small specimen testing methods involve complex stresses which are also heterogeneous. Therefore, there is a certain amount of empiricism while characterizing mechanical properties using these methods. However, being material non-intensive, these methods have applications and advantages over conventional methods namely in material development, material performance evaluation, and characterization of mechanical properties of weld joints. This paper presents a comprehensive review of the recent advances in IC, SPC, and BI testing techniques and discusses their relative advantages and limitations.

The development of highly innovative techniques and technologies to enhance performance and technical sustainability of materials used in the field of cultural heritage conservation is providing conservators with innovative nanocomposites materials, including protective coatings, by merging the performances of engineered nanoparticles (NPs) with conventional chemicals. However, the human health and environmental risks that may potentially arise from these new materials are still largely unknown, requiring an adequate assessment and management along their entire life cycle. Concerns could emerge due to the leaching of the material containing NPs or of the NPs alone, especially during their use (exposure of the treated object to, e.g., heavy or acid rain) and disposal (when the wasted product is processed in, e.g., waste water treatment plants). To date, no standard leaching test methods have been specifically developed for nano-enabled products, with the consequent lack of data on the NPs potential exposure also in the field of cultural heritage. Therefore, an extensive review over the last 10 years by querying to the Scopus database “nanoparticles”, “leaching” and “coatings” has been herein reported to clearly highlight (i) the standard test methods used or adapted to estimate the NPs leaching from nano-based coatings; (ii) the available studies in which the NPs leaching from nano-based coatings was estimated without following any specific standard test method; (iii) the works focusing on other nanocomposite materials performances than leaching, in which standard test methods were applied, potentially useful to indirectly estimate NPs leaching. All the information gathered by this bibliographic search have been used to identify the most promising leaching tests for NPs estimation to be applied in the field of cultural heritage, especially for both large, e.g., building façades, and small, e.g., bronze works of art, surface areas from which the leaching of nano-based materials could be significant in terms of human health and ecological risks, based also on the (eco)toxicity of the leachate. The derived information can thus ultimately support effective risk management of innovative nano-enabled products, including the implementation of Safe by Design approaches.

Upcycling of ligno-cellulosic nutshells waste biomass in biodegradable plastic-based biocomposites uses - a comprehensive review

The growing awareness of the environmental impacts caused by conventional plastic waste has driven the development of more environmentally friendly alternative materials, one of which is biodegradable polymers. This study aims to explore the potential of biodegradable polymers as sustainable and eco-friendly packaging materials. Biodegradable polymers have the ability to decompose naturally through microbial activity under specific environmental conditions, thereby reducing the accumulation of persistent plastic waste. This study presents a literature review of various types of biodegradable polymers, such as polylactic acid (PLA), polyhydroxyalkanoates (PHA), thermoplastic starch (TPS), and polybutylene succinate (PBS), as well as their applications in the packaging industry. Additionally, the study discusses the challenges faced in implementing biodegradable polymers, including relatively high production costs, limitations in mechanical and thermal properties, and specific degradation conditions. Nevertheless, with ongoing technological advancements and increasing consumer awareness of environmental issues, the use of biodegradable polymers in packaging shows promising prospects. This study concludes that biodegradable polymers represent a potential solution to reduce the environmental impact of conventional plastic use, although further research is required to enhance their performance and production efficiency.

Energy release from a substance with relatively low oxygen compatibility is a situation which could result in the ignition and combustion of more oxygen-compatible materials such as the structural metals used in gaseous oxygen systems. At the present time there are no standard ASTM test methods for testing metals ignition and combustion in gaseous oxygen over the range of pressures and purities required for the broad range of oxygen applications which may be encountered. Within recent years, there nas been an increase in the number of metals ignition-combustion studies which have been conducted at pressures in excess of 3.55 MPa. The studies have been conducted under both flowing and static conditions with different promoter systems. Some of the approaches might form the basis for standard ASTM test methods in metals ignition-combustion in gaseous oxygen. Discussion regarding the influence of various test variables which could affect selection of a standard test method does appear in the literature. This paper discusses experimental results obtained with caroon steel and AISI 316L stainless steel using three different apparatus for characterizing metal-oxygen ignition-combustion tendencies. One test method used a 100 mm diameter static chamber with hydrocarbon and wire promoter. The second test method was similar but the chamber was 8 times larger in volume. In contrast to these approaches the third method was a dynamic or flow tester in which tne gas mixtures were continuously flowed past the test specimen. The oxygen purities of the gas mixtures varied from 40 to 99.998% oxygen. Test data and methods were compared.

Thermal imaging cameras are rapidly becoming integral equipment for first responders for use in structure fires and other emergencies. Currently, there are no standardized performance metrics or test methods available to the users and manufacturers of these instruments. The Building and Fire Research Laboratory at the National Institute of Standards and Technology is developing performance evaluation techniques that combine aspects of conventional metrics such as the contrast transfer function (CTF), the minimum resolvable temperature difference (MRTD), and noise equivalent temperature difference (NETD) with test methods that accommodate the special conditions in which first responders use these instruments. First responders typically use thermal imagers when their vision is obscured due to the presence of smoke, dust, fog, and/or the lack of visible light, and in cases when the ambient temperature is uncomfortably hot. Testing has shown that image contrast, as measured using a CTF calculation, suffers when a target is viewed through obscuring media. A proposed method of replacing the trained observer required for the conventional MRTD test method with a CTF calculation is presented. A performance metric that combines thermal resolution with target temperature and sensitivity mode shifts is also being investigated. Results of this work will support the establishment of standardized performance metrics and test methods for thermal imaging cameras that are meaningful to the first responders that use them.

With the thrombogenic tendency and permanent implant nature of metallic stents, synthetic polymers have been proposed as candidate materials for stents and local drug delivery designs. We investigated the biocompatibility of several synthetic polymers after experimental placement in the coronary artery. Five different biodegradable polymers (polyglycolic acid/polylactic acid [PGLA], polycaprolactone [PCL], polyhydroxybutyrate valerate [PHBV], polyorthoester [POE], and polyethyleneoxide/polybutylene terephthalate [PEO/ PBTP]) and three nonbiodegradable polymers (polyurethane [PUR], silicone [SIL], and polyethylene terephthalate [PETP]) were tested as strips deployed longitudinally across 90 degrees of the circumferential surface of coil wire stents. Appropriately sized polymer-loaded stents were implanted in porcine coronary arteries of 2.5- to 3.0-mm diameter. Four weeks after implantation, stent patency was assessed by angiography followed by microscopic examination of the coronary arteries. The biodegradable PCL, PHBV, and POE and the nonbiodegradable PUR and SIL evoked extensive inflammatory responses and fibrocellular proliferation (thickness of tissue response: 0.79 +/- 0.22, 1.12 +/- 0.01, 2.36 +/- 0.60, 1.24 +/- 0.36, and 1.43 +/- 0.15 mm, respectively). Less but still severe responses were observed for the biodegradable PGLA and PEO/PBTP (0.46 +/- 0.18 and 0.61 +/- 0.23 mm, respectively) and for the nonbiodegradable PETP (0.46 +/- 0.11 mm). An array of both biodegradable and nonbiodegradable polymers has been demonstrated to induce a marked inflammatory reaction within the coronary artery with subsequent neointimal thickening, which was not expected on the basis of in vitro tests. The observed tissue response may be attributable to a combination of parent polymer compound, biodegradation products, and possibly implant geometry.

The stability of polymers against environmental factors, chemicals, microorganisms, and hydrolysis has challenged society with the accumulation of plastic waste and its management worldwide. Large amounts of plastic litter accumulate in the environment and disintegrate into microplastics (small pieces less than 5 mm in size), a topic of real concern especially for products and applications where the plastics are used for a short time before becoming waste, and where they are difficult to recover after use and remain in the environment. Whether biodegradable polymers can be one of the solutions to the problem of plastic waste is a question very often raised in this context. Although the use of biodegradable polymers appears to be highly promising based on recent and past studies, several aspects need to be considered further regarding environmental sustainability, acceptability, and degradability in the complex natural environment. Intensive efforts need to be invested in developing new environmentally biodegradable polymers and smart mechanisms of degradation after use in the environment. The present viewpoint article discusses the present scenario of the environmental acceptability of biodegradable polymers and the opportunities and challenges they offer regarding solving the problem of microplastics and their impact on the environment.