Environmental biodegradation of synthetic polymers I. Test methodologies and procedures

Biodegradation of synthetic polymers is an important property that is used in many applications. Evaluation of the extent of biodegradation has used different methods in recent years. For each environmental compartment, different approaches have to be made in order to obtain valuable data on biodegradability.This review describes validated and accepted methods based on standardized biodegradation tests, analytical tests, enzymatic tests or tests of physical properties to evaluate the biodegradability of synthetic polymers for different types of environmental compartments (e.g., soil, compost or aqueous media).Part II of this review will subsequently report on the environmental biodegradation of different groups of synthetic polymers.     

Hydrogel‐coated polyurethane/urea shape memory polymer foams

Shape memory polymers (SMPs) are a class of responsive polymers that have attracted attention in designing biomedical devices because of their potential to improve minimally invasive surgeries. Use of porous SMPs in vascular grafts has been proposed because porosity aids in transfer of fluids through the graft and growth of vascular tissue. However, porosity also allows blood to leak through grafts so preclotting the materials is necessary. Here hydrogels have been synthesized from acrylic acid and N‐hydroxyethyl acrylamide and coated around a porous SMP produced from lactose functionalized polyurea‐urethanes. The biocompatibility of the polymers used to prepare the cross‐linked shape memory material is demonstrated using an in vitro cell assay. As expected, the hydrogel coating enhanced fluid uptake abilities without hindering the shape memory properties. These results indicate that hydrogels can be used in porous SMP materials without inhibiting the shape recovery of the material. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1389–1395     

Processing of aromatic thermosetting copolyesters into foams and bulk parts: characterization and mechanical properties

Fully dense sheets of aromatic thermosetting copolyester (ATSP) have been produced by blending ATSP oligomers, curing the blend to produce foam, grinding the cured material to a powder, followed by sintering of the cured powers via hot press. The resulting product possesses an excellent combination of mechanical strength and high‐temperature performance to help improve part functionality, gain long‐term reliability, and cost savings. Dynamic mechanical analysis of this system featured a glass transition higher than most available performance thermosets and thermoplastic polymers or reversible bonding polymer system described in literature. Compression and tensile properties of the foam and fully dense ATSP structures exceed those of most engineering polymers. Copyright © 2016 John Wiley & Sons, Ltd.     

Bacterial polyhydroxyalkanoates-eco-friendly next generation plastic: Production,biocompatibility, biodegradation,physical properties and applications

ABSTRACT

Polyhydroxyalkanoates (PHAs) are intracellular aliphatic polyesters synthesized as energy reserves, in the form of water-insoluble, nano-sized discrete and optically dense granules in cytoplasm by a diverse bacteria and some archae under conditions of limiting nutrients in the presence of excess carbon source. Bacteria synthesize different PHAs from coenzyme A thioesters of respective hydroxyalkanoic acid, and degrade intracellularly for reuse and extracellularly in natural environments by other microorganisms. In vivo, PHAs exist as amorphous mobile liquid and water-insoluble inclusions but in vitro, exhibit material and mechanical properties, ranging from stiff and brittle crystalline to elastomeric and molding, similar to petrochemical thermoplastics. Further, they are hydrophobic, isotactic, biocompatible and exhibit piezoelectric properties. But as commodity plastics their applications are limited by high production cost, low yield, in vivo degradation, complexity of technology and difficulty of extraction. Therefore, to replace the conventional plastic with PHAs, it is prerequisite to standardize the PHA production systems.     

Evaluation of PFO formation from the biodegradation of a fluorotelomer-based urethane polymer product in aerobic soils

This study is the first to evaluate the rate of formation of perfluorooctanoate (PFO) from the aerobic biodegradation of a fluorotelomer-based urethane polymer and to use this information to assess the global environmental significance of this source. A fluorotelomer-based urethane polymer product test substance was studied in four aerobic soils over two years to determine the rate at which the fluorotelomer side-chains covalently bonded to the polymer backbone were cleaved and subsequently transformed to form the anions of perfluorocarboxylic acids including PFO. Over the two year duration of the experimental study, a polymer biodegradation half-life of 102 years (range: 28-241) was calculated for the urethane polymer based on regression analysis of the rate of PFO formation in four test soils. When this half-life was applied to the estimated total historic production, use and disposal of fluorotelomer-based urethane polymer, the annual potential global generation of PFO was estimated to be less than one tonne per year.     

Shock absorption properties of synthetic sports surfaces: A review

Repeated impact loading during running is a risk factor in the etiology of overuse injuries. Shock absorption can reflect the degree of force attenuation when the heel lands first during movement. This study summarizes the major achievements in the existing literature regarding shock absorption from the engineering perspective and then suggests directions for further investigation. Studies have explained the influencing factors related to shock absorption from the synthetic sports surface itself. Some special measurement methods that can be used to assess vertical and horizontal shock absorption simultaneously are discussed. Numerical simulations related to shock absorption are reviewed, including how to acquire a constitutive model of the sports surface and simulate the manner of loading. Future work should aim to build “player movement‐surface structure and material‐player performance” relationship systems, with more accurate measurements of shock absorption properties in the vertical and horizontal directions and numerical models that can truly reflect actual movements. Solving these problems can strengthen the theoretical and practical understanding of the relationship between synthetic sports surfaces and injury, and athletes can develop more expert performance with fewer injuries.     

The analysis of synthetic organic materials—A review

Synthetic organic materials consist of polymers, low-molecular-weight additives, and fillers. The review deals with the characterization of the polymer portion in the solid state by inelastic interactions with X-rays and by mass spectrometry (MS). Field desorption MS, secondary ion MS, fast atom bombardment MS, and plasma desorption MS have been used in a molar mass range up to 50000 g/mol. Electrospray or laser desorption MS enable samples of even higher molar mass to be investigated.     

An overview of synthetic modification of nitrile group in polymers and applications

The physicochemical properties of polymers are mainly dependent on the nature of polymer backbone and/or pendant groups linked to the main chain. Therefore, synthetic modification of these functional groups via post functionalization is an important approach for obtaining novel polymeric systems with improved properties and targeted applications. In this context, the synthetic modifications of nitrile group in polymers into various useful functionalities have received considerable attention and several interesting applications of the resulting polymers have been identified. The majority of the studies are based on Polyacrylonitrile (PAN), and some isolated examples of nitrile functionalization in copolymers such as Poly (Styrene-co-Acrylonitrile) (SAN), Poly (Acrylonitrile-co-Butadiene-co-Styrene (ABS) and Nitrile Rubber (NBR) are available. These synthetic modifications are mainly accomplished by the reactions such as Nucleophilic addition, cycloaddition, reduction, and hydrolysis using various reagents. These studies describing the post-polymerization modifications of nitrile group in polymers reported during the last three decades are covered in this review.     

Metal foams: A survey

The current state-of-the-art in the development of cellular metal foams is reviewed, with focus on their fabrication, mechanical/thermal/acoustic properties, and potential applications as lightweight panels, energy absorbers, heat exchangers, and acoustic liners. Foam property charts with scaling relations are presented, allowing scoping and selection through the use of material indices.     

软质聚氨酯泡沫塑料用无卤阻燃剂的研究

本文以羟基苯氧膦丙烯酸(CEPP)和三聚氰胺(MA)为原料合成了一种含磷、氮无卤阻燃剂(CMA),采用FT-IR表征了阻燃剂的化学结构,并将该阻燃剂用于软质聚氨酯泡沫(FPUF)的阻燃。用扫描电镜(SEM)研究了阻燃剂的加入对FPUF的形态的影响,通过LO I和垂直燃烧(Cal.117A)测试研究了该阻燃剂对FPUF的阻燃效果。结果表明,CMA可以有效提高FPUF的阻燃性:当CMA的添加量为10%时,FPUF即可通过Cal.117A测试,其LO I值也从17.3提高到23.0;随阻燃剂添加量的增加,FPUF的阻燃性能也逐渐提高。TG测试结果表明CMA的加入对FPUF的热稳定性没有多大影响。     

A new biaxial compression fixture for polymeric foams

This article presents a new biaxial compression test fixture designed for polymeric foam materials. The main advantage of the new fixture is that it is designed for uniaxial testing machines, therefore the biaxial compression measurement does not require a multiaxial test system. The geometries of the fixture and the test specimen, respectively, ensure equibiaxial loading conditions. In order to demonstrate the performance of this new device, equibiaxial measurements of a polymeric foam material are presented. The particular material under consideration is a closed-cell polyethylene foam. In addition, the relation between uniaxial compression tests and equibiaxial compression tests are presented.     

单宁聚氨酯土壤微生物降解研究

采用凝胶渗透色谱仪(GPC)、傅立叶变换红外光谱仪(FT-IR)和电子扫描显微镜(SEM)等实验手段,考察了单宁聚氨酯(WT-PU)在土壤微生物降解前后的化学结构与微观形态的变化,而作为比较用的模型化合物(TMP-PU)在同样的条件下几乎没有变化。结果表明单宁一这交联点在PU整体中以无规降解的方式优先降解,在整个降解过程中,不仅伴随着PU硬段的氢键减弱,软段的氢键也同样有相当的减弱。     

Towards novel super‐elastic foams based on isoperene rubber: Preparation and characterization

A novel and conventional closed cell polyisoprene rubber (IR) foams were produced by a single step limited‐expansion and two step unlimited‐expansion foaming process, respectively. The effect of 3 to 12 part per hundred rubber (phr) of azodicarbonamide (ADC) foaming agent on their structure and properties of developed novel foams were studied. In developed novel foams, the density was strangely independent of ADC content; however, the cell sizes conversely related to ADC content and it decreased by 60% (555‐330 μm) and the internal cell pressure build up from 1 to 3.7 atm, which was related to pressure‐free foaming method. The both reasons of compressed gas trapped inside cells and constant density not only caused unique enhancement in novel foams mechanical properties as hardness and modulus but also improved their dynamic properties as hysteresis and elasticity. Results of conventional IR foams showed that, their foam density as well as dynamic and mechanical properties sharply decreased with increasing ADC content from 3 to 12 phr. For clear expression, in samples with 12 phr of ADC, novel developed foams have more foam density (180%), more hardness (240%), more modulus (290%), and smaller cell size (75%) than conventional foams. Finally, novel developed foams were super‐elastic material with no hysteresis and no plastic deformation while conventional foams had 40% hysteresis and 10% plastic deformation under the same compression conditions.     

In situ preparation of cross‐linked polystyrene/poly(methyl methacrylate) blend foams with a bimodal cellular structure

In situ preparation of a cross‐linked poly(methyl methacrylate) (PMMA) and polystyrene (PS) blend and its foaming were investigated for creating a bimodal cellular structure in the foam. Methyl methacrylate (MMA) monomer was dissolved in PS under supercritical CO₂ at a temperature of 60 °C and a pressure of 8 MPa, and the polymerization of MMA was conducted at 100 °C and 8 MPa CO₂, with a cross‐linking agent in PS. The blend was successively foamed by depressurizing the CO₂. CO₂ played the roles of plasticizing the PS and enhancing the monomer dispersion in PS during the sorption process and as a physical blowing agent in the foaming process. The cross‐linking agent was used for controlling the elasticity of polymerized PMMA domains and differentiating their elasticity from that of the PS matrix. The difference in elasticity delayed the bubble nucleation in the PMMA domains from that in the PS and made the cell size bimodal distribution, in which the smaller cells ranging from 10 to 30 µm in diameter were located in the wall of large cells of 200–400 µm in diameter. The effects of the initial MMA content, the concentration of cross‐linking agent, and the depressurization rate on the bimodal cell structure and bulk foam density were investigated. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigation on properties of aqueous foams stabilized by aliphatic alcohols and polypropylene glycol

Foams stabilized by nonionic surfactants are usually moderately stable due to high drainage rate and intense bubble coalescence and coarsening. This study aimed to investigate comparatively the foam properties of aliphatic alcohols (methyl isobutyl carbinol (MIBC) and 2-octanol) and polypropylene glycol (PPG400). Experiments were conducted using the FoamScan method at various surfactant concentrations and gas flow rates where the foam volume, liquid content of foam and foam half-life were determined. The results showed that both foamability and foam stability of surfactant solution increased with increasing gas flow rate and surfactant concentration for all tested surfactants. PPG400 was an unusually strong surfactant having the largest surface activity compared with MIBC and 2-octanol, which exhibited the maximum foaming performance and foam stability at all tested gas flow rates and concentrations. The present study suggested that foam properties depended primarily on the type of surfactant and its concentration and secondarily on the gas flow rate. In addition, properties of interface are closely related to that of foam, which is a significant point if one wants to produce foams for specific applications.     

Stimuli-responsive liquid foams: From design to applications

Stimuli-responsive liquid foams and bubbles are systems for which the stability, structure, shape, and movement can be controlled by the application of stimuli. The foam stability can be modified by a stimulus which can change solution condition (pH, temperature, and ionic strength) or with the application of an external field (light and magnetic). Different foam stabilizers have been described in the literature to design these responsive foams systems ranging from surfactants, peptides, polymers, soft polymer particles, surfactants self-assembly, crystalline particles, emulsion droplets, and solid particles. This review aims to cover the recent advances of the design of stimuli-responsive liquid foams and their applications. Responsive liquid foams are attractive in textile coloring process, biomedical application, washing, and material recovery processes.     

Oxidation and biodegradation of polyethylene films containing pro-oxidant additives: Synergistic effects of sunlight exposure, thermal aging and fungal biodegradation

Synergistic effects of sunlight exposure, thermal aging and fungal biodegradation on the oxidation and biodegradation of linear low density poly(ethylene) PE-LLD films containing pro-oxidant were examined. To achieve oxidation and degradation, films were first exposed to the sunlight for 93 days during the summer months followed by their incubation with fungal strains previously isolated from the soil based on the ability to grow on the oxidized PE-LLD as a sole carbon source. Some films were also thermally aged at temperatures ranging between 45°C and 65 °C, either before or after fungal degradation. Films with pro-oxidant additives exhibited a higher level of oxidation as revealed by increase in their carbonyl index (COi). In addition to increase in the COi, films showed a slight increase in crystallinity and melting temperature (T_m), considerably lower onset degradation temperatures, and a concomitant increase in the % weight of the residues. The level of oxidation observed in thermally aged films was directly proportional to the aging temperature. The PE-LLD films with pro-oxidant exposed to sunlight followed by thermal aging showed even higher rate and extent of oxidation when subsequently subjected to fungal biodegradation. The higher oxidation rate also correlated well with the CO₂ production in the fungal biodegradation tests. Similar films oxidized and aged but not exposed to fungal biodegradation showed much less degradation. Microscopic examination showed a profuse growth and colonization of fungal mycelia on the oxidized films by one strain, while another spore-producing strain grew around the film edges. Data presented here suggest that abiotic oxidation of polymer's carbon backbone produced metabolites which supported metabolic activities in fungal cells leading to further biotically-mediated polymer degradation. Thus, a combined impact of abiotic and biotic factors promoted the oxidation/biodegradation of PE-LLD films containing pro-oxidants.     

Non-isothermal degradation kinetics of MMA-St copolymer and EPS lost foams

Methylmethacrylate-styrene (MMA-St) random copolymer was synthesized by suspension copolymerization. The thermal degradation of MMA-St copolymer and EPS lost foams was studied by non-isothermal thermal gravimetric analysis under nitrogen purge. Thermal decomposition behavior of MMA-St copolymer lost foam was examined and compared with EPS. It was found that EPS foam starts to decompose at higher temperatures than MMA-St copolymer foam in all heating rates. The apparent activation energy was calculated by the Flynn-Wall-Ozawa method. It has been concluded that the model fitting methods unable to reveal the complexity of the pyrolysis process and the model-free methods can be suggested as a reliable way of determining the kinetic parameters.     

Measurement of pressure distribution in the Plateau borders of fresh and aged foams

In the interpretation of foam ageing processes it is important to know the laws of fluid motion in the Plateau borders. In foams, the rate of fluid motion is determined, in principle, by the fluid viscosity, the static and dynamic surface tension, the shape of the capillaries and the pressure distribution. An attempt is made to investigate the role of these parameters experimentally. As a first step, the pressure and the pressure distribution were measured in the Plateau borders by liquid-filled manometers kept in contact with the Plateau borders through a porous plate. The pressure is always negative, and the pressure vs. time curves show maxima at the point of the start of draining. Draining starts when pressure difference drops to zero at the bottom of the foam container. After a sufficiently long time the pressure becomes equal to the hydrostatic pressure at the given level, i. e. _p=–gh, where is the density of the liquid andh is the height of the foam column measured from the bottom of the container.