Common to liquids, solids and substances in between the former two is that if a stress is applied to them, they will strain. Stress may be visualized by placing a small amount of fluid between two parallel plates. When one plate slides over the other, forces act on the fluid dependent upon the rate of the plate movement. This causes a shear stress on the liquid. Recall laminar flow of fluids through a tubular vessel. Strain is the response to the stress. If solids are elastic, they deform and return to their original shape. Since fluids are not elastic and, hence, viscous, their deformation is irreversible.

Introduction to rheology

Biodegradation of bioplastics in natural environments.

The fundamentals of coating tribology are presented in a generalised holistic approach to friction and wear mechanisms of coated surfaces in dry sliding contacts. This is based on a classification of the tribological contact process into macromechanical, micromechanical, tribochemical contact mechanisms and material transfer. The tribological contact process is dominated by the macromechanical mechanisms, which have been systematically analysed by using four main parameters: the coating-to-substrate hardness relationship, the film thickness, the surface roughnesses and the debris in the contact. The description covers both soft and hard coatings with thicknesses typically in the range 0.1–50 μm, where the interaction between the coating and the substrate is essential to the tribological behaviour. The concept is supported by experimental observations. The important influence of thin tribo- and transfer layers formed during the sliding action is shown. Optimal surface design both regarding friction and wear can be achieved by new multilayer techniques giving reduced stresses, improved adhesion to substrate, more flexible coatings and harder and smoother surfaces. The differences in contact mechanisms in dry, water- and oil lubricated contacts with coated surfaces is illustrated by experimental results from diamond-like coatings sliding against a steel ball. The mechanisms of the formation of dry transfer- and tribolayers and lubricated boundary and reaction films are discussed.

Tribology of thin coatings

Effect of thermo-mechanical cycles on the physico-chemical properties of poly(lactic acid)

The problems linked to plastic wastes have led to the development of biodegradable plastics. More specifically, biodegradable bioplastics are the polymers that are mineralized into carbon dioxide, methane, water, inorganic compounds, or biomass through the enzymatic action of specific microorganisms. They could, therefore, be a suitable and environmentally friendly substitute to conventional petrochemical plastics. The physico-chemical structure of the biopolymers, the environmental conditions, as well as the microbial populations to which the bioplastics are exposed to are the most influential factors to biodegradation. This process can occur in both natural and industrial environments, in aerobic and anaerobic conditions, with the latter being the least researched. The examined aerobic environments include compost, soil, and some aquatic environments, whereas the anaerobic environments include anaerobic digestion plants and a few aquatic habitats. This review investigates both the extent and the biodegradation rates under different environments and explores the state-of-the-art knowledge of the environmental and biological factors involved in biodegradation. Moreover, the review demonstrates the need for more research on the long-term fate of bioplastics under natural and industrial (engineered) environments. However, bioplastics cannot be considered a panacea when dealing with the elimination of plastic pollution.

Biodegradation of Wasted Bioplastics in Natural and Industrial Environments: A Review

Influence of the recycled material percentage on the rheological behaviour of HDPE for injection moulding process.

Method for generation of rheological model to characterize non-conventional injection molding by means of spiral mold

The influence of environmental conditions on the dimensional stability of components injected with PA6 and PA66

The influence of the painting process on a biocompostable waste is studied. Disintegration degree (D %) of a 100% biocompostable plastic made from potato almidon is calculated for both painted and non -painted samples. Solid matrix is also characterized by means of a laboratory scaled composting process following UNE-EN norms [2, 3]. It can be concluded that painting has a negative influence on biocomposting process decreasing 4.48% disintegration degree. Average D% for painted samples is 84.56 %, and 89.04 for nonpainted ones. Regarding to solid matrix, dry mass after composting is double (91.12 %) as before process (43.63 %) for painted samples and 91 % and 45.41 % after and before composting for non-painted samples. Volatile solids are reduced 5.17 % after composting for painted samples, and 8.78 % for nonpainted. Organic nitrogen is reduced 0.34 % and 0.16% for painted and non-painted samples respectively. The negative effect of painting is mainly due to the barrier effect of the paint that prevents microorganisms from converting organic components of the biopolymer into water, CO 2 and compost.

Study of the Biodisintegration on a Painted Bioplastic Material Waste

Reducing energy consumption is an important issue for green manufacturing. In this paper, the specific energy consumption (SEC) of the injection molding process is analyzed. Results showed significant variations depending on the injected thermoplastic material and the type of injection molding machine (IMM) suggesting that IMM selection has a high relevance for the efficiency, cost and environmental impact of the process. The manufacturing of 36 plastic parts has been characterized by measuring the electricity consumption and obtaining the environmental impact, being this consumption its most important factor. A descending tendency for both is observed when high throughputs are obtained because the size of the IMM is more optimized. Conversely, the savings obtained by the all-electric IMMs are significant. This research could help engineers to properly select an IMM by taking into account the part weight, material and environmental criteria. Also, this study will be useful for life cycle assessment (LCA) practitioners. Real consumption data is presented, providing details about the materials, and relationships with the IMM that was used. The high variability suggests that if the injection molding process is relevant in a LCA study, its consumption must be analyzed in depth, preferably by measuring real consumptions in the factory.

Influence of material and injection molding machine’s selection on the electricity consumption and environmental impact of the injection molding process: An experimental approach

Isabel Clavería

Papers

Influence of the recycled material percentage on the rheological behaviour of HDPE for injection moulding process.

Method for generation of rheological model to characterize non-conventional injection molding by means of spiral mold

The influence of environmental conditions on the dimensional stability of components injected with PA6 and PA66

Study of the Biodisintegration on a Painted Bioplastic Material Waste

Influence of material and injection molding machine’s selection on the electricity consumption and environmental impact of the injection molding process: An experimental approach