Mechanical behaviour of biodegradable agricultural films under real field conditions

The mechanical behaviour of various types of biodegradable materials depends on their chemical composition and additives, the processing characteristics and the application conditions. The environmental conditions during storage and usage of these materials strongly influence their mechanical properties and behaviour. Ageing and degradation during the useful lifetime of biodegradable agricultural films causes losses in the mechanical performance of the material, as measured by monitoring the evolution of some of the critical mechanical properties. Such losses may be comparable to the corresponding losses of the conventional polyethylene agricultural films due to ageing, or they may be more drastic. In the present paper, the overall mechanical and ageing/degradation behaviour of experimental specially designed and manufactured low-tunnel and mulching biodegradable films, exposed to full-scale field conditions is analysed. Selected critical mechanical properties of these films manufactured with different grades of Mater-Bi material and additives, different thickness and processing schemes and exposed to real cultivation conditions in four different locations in Europe are investigated in the laboratory and compared against the corresponding behaviour of conventional agricultural films at various stages of their exposure time.     

Influence of typical stabilizers on the aging behavior of EVA foils for photovoltaic applications during artificial UV-weathering

Ethylene vinyl acetate copolymer (EVA) is the most commonly used embedding material in crystalline silicon photovoltaics. It is responsible for fixing module components, electrical isolation and protecting cells against mechanical and environmental stresses. The degradation of EVA during weathering can cause adhesion loss, the so called delamination, and yellowing of the foil, resulting in a drop of module efficiency. In order to improve the long-term stability, several stabilizers including UV-absorber, hindered amine light stabilizer and phosphite are added to the polymer. However, the exact influence of the different stabilizers on failure mechanisms has not yet been identified in detail. Therefore, different EVA foils containing variable additive formulations were exposed to artificial UV-irradiation at 50 °C. As a result, delayed EVA degradation could be observed depending on stabilizers added. On the other hand, some of the tested additives were found to be involved in delamination and yellowing processes.     

Monitoring of the degradation dynamics of agricultural films by IR thermography

The high consumption of plastic materials for use in agriculture is generating serious problems regarding environmental impact. Biodegradable materials are at present the only solution to this type of problems. Research in material science is daily proposing different materials with this requirement for application in various sectors. One of the problems is to analyse the degradation states of the films before their application in order to know the time and the modality of degradation. Here we propose a novel method based on thermography vs time which allows the degradation dynamics of agricultural films to be evaluated.In our experiment we put some biodegradable materials of our interest on soil in an open field. The main characteristic of these materials is that they are originally liquid and they are sprayed on soil and immediately cross-link into a film state. Through an IR thermal camera we monitored the state of the films day by day and analysed the thermal images in order to detect the continuous changing of their physical properties.     

Effects of reprocessing of oxobiodegradable and non-degradable polyethylene on the durability of recycled materials

The use of plastics is steadily increasing in our daily lives, and plastics are the fastest-growing component of the waste stream. Although the efficiency of plastic recycling is increasing, plastics are often seen as a permanent environmental problem because of littering. The introduction of oxobiodegradable polyolefins (OBDs), containing prodegradant additives, is considered to be a way to reduce this problem by enabling the fast degradation of plastics in the environment. The prodegradant additives form radicals that attack the polymer chains, causing chain scissions and generation of low molecular mass oxidation products that can be consumed by microorganisms. There is, however, a concern that the prodegradant additives will present a problem if OBD materials end up in the conventional plastic recycling streams. The present study therefore highlights the impact of mixing OBD materials with conventional polyolefins to evaluate the impact on the remaining service life of the recyclates.The study included the use of two different OBDs, mixed in different proportions (10% and 20%) in a conventional polyethylene. The remaining service life of the mixtures was evaluated by monitoring the reduction in tensile strain after exposure to thermo-oxidative degradation at 70 °C, compared with a pure polyethylene. The impact of stabilizer content in the mixtures was also evaluated together with the effect of mixing partially degraded OBDs into the recyclate.The results show that the incorporation of minor fractions of OBD materials in the existing recycling streams will not create a severe effect on the service life of the recyclates as long as the polymer mixture possesses a reasonable degree of stabilization.     

Photodegradable plastics: end-of-life design principles

Abstract

Photochemically degradable polymers and plastics are reviewed with an emphasis on the environmental and molecular factors that control the onset of degradation and the rate of degradation. A number of principles are beginning to emerge for the design of viable photochemically degradable plastics. Among the principles discussed are those relating to the effects of chromophores, initiators, antioxidants, temperature, oxygen diffusion into the plastic, polymer crystallinity, tensile and compressive stress, and the absorbed light intensity on the plastic. To obtain a plastic with a controlled lifetime and a specific rate of degradation, many of these parameters can be controlled or adjusted in the design stage of the plastic.     

解决白色污染的技术研究进展

随着经济的发展,废旧塑料大幅增加,所造成的白色污染已经成为了破坏环境的主要因素之一。白色污染主要是由废旧塑料高分子的不可降解性和添加剂的毒害性引起的。目前,各国都在解决白色污染的技术方面进行了大量的研发投入。文章主要综述了可降解塑料的研发和对废旧塑料回收再利用技术的研发两方面的研究进展。     

How will additives shape the future of plastics?

Additives are essential components of plastic formulations providing maintenance and/or modification of polymer properties, performance and long-term use. The extension of polymer properties by additives has played a substantial role in the growth of plastics. At the beginning of the plastics age additives were used mainly to maintain polymer properties and to help plastics to survive heat treatment during transforming processes. The next generation of additives provided extension of service life as well as modification of mechanical and physical properties. These well-established additives - antioxidants, heat stabilizers, light stabilizers and others - cover the requirements of standard plastics and today's mass applications. The more recent developments of high-performance additives address more stringent or new requirements, more severe processing and use conditions and/or environmental concerns, but still with the main target of maintaining plastic properties. The future will introduce more and more new effects and functionalities through additives in plastic applications tailoring the properties of polymers and offering a vast potential of innovation in the plastics area. Recent examples of emerging technologies show that additives will not only modify the polymer itself and add new properties, but can also, when incorporated into the plastic, beneficially impact properties, which are of high value for the user. The paper shows the role of additives used in plastics from the past to the present with the focus on stabilization and performance of additives incorporated during melt processing, and outlines future trends.     

Abiotic and biotic degradation of oxo-biodegradable polyethylenes

Conventional polymeric materials accumulate in the environment due to their low biodegradability. However, an increase in the biodegradation rate of these polymers may be obtained with the addition of pro-degrading substances. This study aimed to evaluate abiotic and biotic degradation of polyethylenes (PEs) using plastic bags of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) formulated with pro-oxidant additives as test materials. These packaging materials were exposed to natural weathering and periodically analyzed with respect to changes in mechanical and structural properties. After a year of exposure, residue samples of the bags were incubated in substrates (compost of urban solid waste, perlite and soil) at 58 °C and at 50% humidity. The biodegradation of the materials was estimated by their mineralization to CO₂. The molar mass of the pro-oxidant-activated PE decreased and oxygen incorporation into the chains increased significantly during natural weathering. These samples showed a mineralization level of 12.4% after three months of incubation with compost. Higher extents of mineralization were obtained for saturated humidity than for natural humidity. The growth of fungi of the genera Aspergillus and Penicillium was observed on PE films containing pro-oxidant additives exposed to natural weathering for one year or longer. Conventional PE films exposed to natural weathering showed small biodegradation.     

Characterization of polymer soil burial degradation by thermal analysis and mechanical spectroscopy

Polypropylene (PP) and High density polyethylene (HDPE) / Polypropylene (PP) blend with different biodegradable additives (Granular starch/iron oxide mixture, Bioefect 72000 and Mater-Bi AF05H) were selected for degradation experiments. All the samples, processed by injection as seedboxes, have been subjected to an outdoor soil burial test and removed at different periods of time between 0 and 21 months. Their chemical structure and morphology have been analysed. Studies of dynamic-mechanical relaxation spectra of the samples before and after each exposure time have been carried out. The three characteristic relaxation zones α, β and γ, in order of decreasing temperature, have been obtained. It has been observed that due to the degradation process both, the HDPE/PP blend and the PP matrix, become more brittle than the undegraded ones regardless of the additive used. Degradation seems to start from the molecular chains of the amorphous phase or interfacial region. However the analysis of the mechanical behaviour manifested that the crystalline zone is also been affected by the exposure time.     

Effect of several variables in the polymer toys additive migration to saliva

Capacity to migrate of a representative group of polymeric additives, dyes, antioxidants, hindered amine light stabilizers (HALS) or antistatics, from plastic toys to saliva was analyzed to protect children in their habits of sucking and biting. Most of target additives appear no-regulated in toys normative but adverse effects on human health of some of them have been demonstrated and their presence in others commercial articles normative has been included.In order to offer an effective and easy tool to perform these controls, migration tests by dynamic and static contact, followed by a preconcentration step by liquid-liquid extraction (LLE) and ultra performance liquid chromatographic analysis with ultraviolet-visible and evaporative light scattering detections (UPLC-UV/Vis-ELSD) have been optimized to evaluate the migrated amounts of the additives in saliva simulant. The detection limits of the migration methodologies were ranged from 8.68 × 10⁻² to 1.30 × 10⁻³ mg migrated (L simulant)⁻¹.Influence of several variables on this mass transport, as time, temperature and friction, was also analyzed to achieve the most aggressive methodology to protect consumers.Migration of several studied additives, whose presence has been demonstrated in several purchased commercial toys, has been observed.     

Rapid determination of oligomeric hindered amine light stabilizers in polymeric materials

Hindered amine light stabilizers are essential for the stabilization of synthetic polymers, particularly for materials used for outdoor applications. Although up to now a considerable number of studies dealing with the analytics of this class of stabilizers had been published, especially the determination of oligomeric hindered amine light stabilizers is still an analytical challenge. In the current work, a fast and simple liquid chromatographic method for the quantitative determination of oligomeric hindered amine light stabilizers is presented. A key aspect of this method is their completely different retention behavior depending on the pH, enabling a single peak elution approach by a pH gradient run. This allows a quantitation with simple UV detection independent of the actual oligomeric composition. Calibration curves within the concentration range relevant for the analysis of real polymer samples (LOQ = 70 mg/L) were constructed with R ² values above 0.99. Spiked extracts from polyolefin samples showed recovery rates between 97.3 and 102.9% for five different commercial hindered amine light stabilizers. Relative standard deviations were between 2.0 and 3.9%. Furthermore, it was demonstrated that the employed approach can be easily adapted for mass spectrometry detection.     

Natural antioxidants for polypropylene stabilization

A study on the efficiency of bio-based compounds as stabilizers for polypropylene (PP) is reported. A water extract from French maritime pine bark (Pycnogenol^®), a by-product containing polyphenols obtained from wine production, and a carotenoid-containing oleoresin from processing of tomatoes were used. Their stabilizing activity was compared with that of a commercial phenolic antioxidant. Thermogravimetric analysis and Oxidative Induction Time measurements performed on unaged samples, as well as infrared spectroscopy on samples aged at 70 °C, provided evidence for the effectiveness of the natural stabilizers. Mechanical characterization was carried out on aged films and injection moulded samples. Experimental results indicated that particularly grape extract could provide long-term stabilization to PP under conditions of oxidative degradation. Therefore, it could be used as efficient and high value-added additive for polypropylene. Pycnogenol^® also showed antioxidant activity, however the achievement of a more homogeneous dispersion in the polymer matrix could improve the mechanical performance of aged samples.     

Determination of polymer additives using analytical pyrolysis

When analyzing a polymeric material using pyrolysis-GC, the majority of the peaks seen are degradation products from the polymer matrix, but there may be specific compounds present resulting from the presence of antioxidants, plasticisers, stabilizers, flame retardants and other additives. Some of these compounds may be volatile or semi-volatile and appear as intact molecules, while others are larger and only appear as fragments after the pyrolysis. In understanding the pyrolysis of the complete system, it is important to understand the behavior of such additives under the thermal conditions used to analyze the polymer matrix.This paper presents data for several polymer additives, showing their contribution to the analytical results when studying typical polymers using Py-GC/MS. Specific types of additives include phenolic antioxidants, hindered amine light stabilizers, phthalates and phosphites.It was determined that for some additives, especially when analyzing simple polymers, co-analysis of the polymer and additive was feasible. For other, more complex formulas, a multi-step approach permitted a thermal separation of compound families and simplified the analysis. For some additives, especially in the parts-per-million range, pyrolysis with selected or extracted ion mass spectrometry was the most informative.     

Stabilization beyond the year 2000

A variety of chemical reactions lead to the oxidative deterioration of polymers upon processing and during end-use of plastic articles. To inhibit the autoxidation cycle, stabilizers interfering at the various steps of the degradation are needed. Complex stabilizer systems which are able to suppress oxidative degradation have been developed recently. Special emphasis is given to radical scavenging, including alkyl radicals. UV absorbers with inherent photostability have led to an enhanced stability of polymers, such as engineering thermoplastics.     

Synthesis, structural study and hydrolytic degradation of copolymer based on glycolic acid and bis-2-hydroxyethyl terephthalate

The current demand for environmentally degradable copolymers has initiated the use of novel degradable copolyesters. One of them is a copolyester based on poly(ethylene terephthalate-co-glycolic acid) (PET-GLA). The copolymer was synthesized by the melt reaction of bis-2-hydroxyethyl terephthalate (BHET) with glycolic acid (GLA) oligomers in the presence of Sb₂O₃ as a catalyst.Hydrolytic degradation of the copolymer was carried out in two buffered solutions at 45 °C: degradation was studied by incubating samples in powder form, in a concentrated solution from 30 to 150 days.The copolymer before and after degradation was characterized by means of different analytical techniques. ¹H and ¹³C NMR spectroscopy was used to confirm the incorporation of glycolide units in PET chains and to observe the structure and decomposition of the novel polyester. The thermal properties and morphology before and during the degradation were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis for determining melting points as well as melting and decomposition temperatures of investigated copolyester.     

Mn2Al-LDH- and Co2Al-LDH-stearate as photodegradants for LDPE film

The layered double hydroxides (LDH) Mn₂Al-LDH-stearate and Co₂Al-LDH-stearate were prepared by a surfactant-assisted intercalation of the corresponding precursor LDH-CO₃ forms. These compounds were evaluated as potential photodegradant additives in low density polyethylene films with a thickness of ca. 40 μm. They were incorporated into blown polyethylene films via a 10% masterbatch. The films were subjected to accelerated ageing in a QUV weatherometer. The machine was fitted with A320 lamps and operated on a dry cycle at 63 °C and an irradiance of 0.67 W/m². It was found that 100 h of QUV exposure was sufficient to cause mechanical embrittlement of films containing as little as 0.1% of either active additive.     

Degradable plastic films for agricultural applications in Taiwan

Tainan District Agricultural Improvement Station began in February 1991 to evaluate the feasibility of using degradable plastic films for horticultural crops production. Products from China, Korea, Israel, Germany, U.S.A. and Taiwan were used for comparison. Results are summarized as follows: Macro-and micro-environmental changes in different seasons affected the degradation time of the tested degradable plastic films. The silver/black bio/photo-degradable PE films containing 20% starch from USI Far East Corporation degraded after 56, 83, 38, and 33 days when they were mulched in fall(October, 1991), winter(December, 1991), spring(April, 1992) and summer (August, 1992), respectively. The more starch incorporated, the faster the films degraded. No difference was observed in size, weight, yield, total soluble solids and heavy metal contents of the fruits of cantaloupe and watermelon grown on the beds mulched with various kinds of degradable PE films or traditional PE film. No difference was observed in yield as well as the heavy metal (Fe, Pb, Ni, Cu, Cd and Cr) contents in the edible part of the crops of cabbage mustard and head lettuce that were grown in the soil without or incorporated with debris of degradable PE films in 6 consecutive years. The same results were also obtained in another trial on cantaloupe and paddy rice for 4 consecutive years. Various amounts(0, 4, 8, 16, 32 and 64g) of used degradable PE films were seperately mixed with field soil. The mixed soil were used to grow paddy rice in clay pots. No difference was observed in plant height, length and weight of the spike, 1,000-seed weight and the kernel per spike among the treatments at harvesting. Six pieces (each 10cm□10cm) of Bioplastics, Bioflex and Green choice biodegradable films were buried in a 8-inch clay pot. Then head lettuce were planted in the pots. No difference was observed in head weight and qualities(vitamin C. total soluble solids and crude fiber)either among the treatments or the control. The weight losses for Bioflex, Bioplastics and Green choice were 58.4%,47.9% and 11.3%, respectively after 40 days.     

Effect of natural antioxidants on the stability of polypropylene films

A preliminary study on the efficiency of agri-food industry wastes as stabilizers for polypropylene (PP) films is reported. Several analytical techniques were employed to evaluate the stabilization effectiveness of the additives. DSC and CL analysis performed on unaged samples confirmed the antioxidant activity of natural additives, and provided the following order of efficiency: red grape seeds > white grape seeds > tomato extracts. The films were also artificially aged at 70 °C, and FTIR spectroscopy confirmed the stabilization trend obtained from the unaged films. Kinetic analysis of TG data alongside tensile tests indicated that the tomato extract is a good thermal and processing stabilizer, but it is sensitive to oxidation. In contrast, grape seeds provide long-term stabilization to PP under conditions of oxidative degradation. Our results show that tomato and wine processing by-products have good potential to be exploited as a low-cost source of value-added phytochemicals.     

Fabrication of flexible AgNW/cellulose hybrid film with heat preservation and antibacterial properties for agriculture application

In the view of sustainable development and environmental protection, degradable agricultural films with on-demand thermal insulation properties have attracted growing research interest in the last few decades due to the deteriorating environment and extreme climate on the growth and existence of crops. Here, a general strategy has been developed to fabricate degradable silver nanowires modified cellulose (AgNW/cellulose) hybrid film with controllable thermal insulation and antibacterial properties by using plant cellulose and AgNWs as building blocks, PVA and PEG as film forming solvent, as well as their agriculture application. The results show that the AgNWs are evenly dispersed in the three-dimensional grid of cellulose, that they form a film that can withstand a certain tensile force and have good thermal stability. Due to the excellent electrical conductivity, the AgNW/cellulose hybrid films can provide excellent Joule heating, generating rapid thermal response and uniform electrical heating at a low supply voltage of 3 V. In the antibacterial tests against Escherichia coli and Staphylococcus aureus, the AgNW/cellulose hybrid films exhibited large diameters of inhibition zones, revealing the high antibacterial activity. Additionally, the AgNW/cellulose hybrid films showed highly stretchable behavior by delivering a breaking strain of 1.5% with a tensile stress of 0.45 MPa owing to the cross-linked structures of cellulose and AgNWs. Based on the above properties, this study not only provides a potential strategy for the fabrication of flexible and biodegradable agricultural films but also may provide new insights for agricultural thermal management.