We present an experimental and theoretical study of the fragmentation of polymeric materials by impacting polypropylene particles of spherical shape against a hard wall. Experiments reveal a power law mass distribution of fragments with an exponent close to 1.2, which is significantly different from the known exponents of three-dimensional bulk materials. A 3D discrete element model is introduced which reproduces both the large permanent deformation of the polymer during impact, and the novel value of the mass distribution exponent. We demonstrate that the dominance of shear in the crack formation and the plastic response of the material are the key features which give rise to the emergence of the novel universality class of fragmentation phenomena. PACS numbers: 62.20.Mk; 46.50.+a; Fragmentation phenomena are ubiquitous in nature and play a crucial role in numerous industrial processes related to mining and ore processing [1]. A large variety of measurements starting from the breakup of heavy nuclei through the usage of explosives in mining or fragmenting asteroids revealed the existence of a striking universality in fragmentation phenomena [1-10]: fragment mass distributions exhibit a power law decay, independent on the type of energy input (impact, explosion, ...), the relevant length scales or the dominating microscopic interactions involved. Detailed laboratory experiments on the breakup of disordered solids have revealed that mainly the effective dimensionality of the system determines the value of the exponent, according to which universality classes of fragmentation phenomena can be distinguished. Several possible mechanisms have been put forward to understand the emergence of the universal power law behavior. For rapid break-up of heterogeneous bulk solids with a high degree of brittleness, the self-similar branching-merging scenario of propagating unstable cracks governed by tensile stresses can explain the main features of the fragment mass distribution [5,[11][12][13], while for shell systems an additional sequential binary breakup mechanism has to be taken into account [7,8]. It is an important question of broad scientific and technological interest how plasticity, and the emergence of complicated stress states like shear affect the fragmentation process. The fundamental questions of how robust the universality classes are with respect to mechanical properties and whether there exist further universality classes of fragmentation of solids, still remain open.In the present Letter we investigate the fragmentation process of plastic materials by impacting spherical particles made of polypropylene (PP) against a hard wall. Our experiments show that the mass distribution of plastic fragments exhibits a power law behavior with an exponent close to 1.2, which is substantially different from the one of bulk brittle materials in three-dimensions. In order to understand the physical origin of the low exponent, a three-dimensional discrete element model is developed where the sample is discretized in terms of ...

When exposed to a surface fire, the probability of a tree to survive widely varies, depending on its capability to protect the cambium from lethal temperatures above 60 °C. Thereby, the bark, the entirety of all tissues outside the cambium, serves as an insulation layer. In laboratory experiments, the heat production of a surface fire was simulated and the time span Tau₆₀ until the temperature of 60 °C is reached in the inner bark surface was measured. Thereby, Tau₆₀ - as a measure of the fire resistance - was quantitatively determined for seven tree species. In addition, the influence of bark thickness and moisture content on bark heat insulation capacities was examined. Independent of the tree species and bark moisture content a power function correlation between bark thickness and Tau₆₀ was found. Our results also show that fire resistance increases with decreasing bark density. The seven tree species examined can be classified in two groups differing highly significant in their bark structure: (1) tree species with a faintly structured bark, which show a low fire resistance, and (2) tree species with an intensely structured bark, showing a high fire resistance. Furthermore a mathematical model simulating heat conduction was applied to describe the experimental results, and some ideas for a transfer into biomimetic materials are presented

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Hollow microspheres are spherically symmetrical particles consisting of at least two phases. Their sales are continuously increasing because of a large number of well-known and new applications. While most of the current needs for hollow microspheres are met by inorganic byproducts of combustion processes (cenospheres), the fabrication of tailor-made hollow sphere structures by processes like spray-drying as well as dripping, emulsion and suspension techniques is gaining more and more interest. Surface phenomena play an important role as far as formation, properties and stability of hollow microspheres are concerned. Template techniques can be used to yield structures that have not been available so far. Modeling and simulation of the formation processes are useful tools to understand the formation mechanisms and to simplify the scaleup.

Purpose Products made of plastic often appear to have lower environmental impacts than alternatives. However, present life cycle assessments (LCA) do not consider possible risks caused by the emission of plastics into the environment. Following the precautionary principle, we propose characterization factors (CFs) for plastic emissions allowing to calculate impacts of plastic pollution measured in plastic pollution equivalents, based on plastics’ residence time in the environment. Methods and materials The method addresses the definition and quantification of plastic emissions in LCA and estimates their fate in the environment based on their persistence. According to our approach, the fate is mainly influenced by the environmental compartment the plastic is initially emitted to, its redistribution to other compartments, and its degradation speed. The latter depends on the polymer type’s specific surface degradation rate (SSDR), the emission’s shape, and its characteristic length. The SSDRs are derived from an extensive literature review. Since the data quality of the SSDR and redistribution rates varies, an uncertainty assessment is carried out based on the pedigree matrix approach. To quantify the fate factor (FF), we calculate the area below the degradation curve of an emission and call it residence time $${\tau }_{R}$$ τ R . Results and discussion The results of our research include degradation measurements (SSDRs) retrieved from literature, a surface-driven degradation model, redistribution patterns, FFs based on the residence time, and an uncertainty analysis of the suggested FFs. Depending on the applied time horizon, the values of the FFs range from near zero to values greater than 1000 for different polymer types, size classes, shapes, and initial compartments. Based on the comparison of the compartment-specific FFs with the total compartment-weighted FFs, the polymer types can be grouped into six clusters. The proposed FFs can be used as CFs which can be further developed by integrating the probability of the exposure of humans or organisms to the plastic emission (exposure factor) and for the impacts of plastics on species (effect factor). Conclusions The proposed methodology is intended to support (plastic) product designers, for example, regarding materials’ choice, and can serve as a first proxy to estimate potential risks caused by plastic emissions. Besides, the FFs can be used to develop new CFs, which can be linked to one or more existing impact categories, such as human toxicity or ecotoxicity, or new impact categories addressing, for example, potential risks caused by entanglement.