Plastics pyramid

Over the past decade, researchers and citizen advocates have developed several tools to assist in decision making about plastics selection. The plastics pyramid (Fig. 5.1] developed by Thorpe and Van der Naalde in 1998 was an early attempt to visually display the life cycle hazards of different plastics to assist in materials selection. This ranking focused on the toxicity of the material, considering production hazards, use of harmful additives, hazards in use, and disposal hazards. In this pyramid, bio-based polymers form the bottom of the pyramid, indicating they are most preferable, as they are made from renewable resources, and theoretically are biodegradable and compostable (Rosalia et al., 2012]. 

Figure 5.1 The plastics pyramid. Reproduced with permission from Rosalia et al. (2012).

Since the Plastics Pyramid (Fig. 5.1) was developed, bio-based plastics are much further along in their commercial development These materials need to be evaluated carefully for sustainability. Later on the Plastic Spectrum (Table 5.1) and Plastics Scorecard were also made in order to rate different types of plastics based on their life cycle impacts and hazards to human health and environment... 

The product ETFE was first marketed in 1970 by the DuPont company under the name Tefzel . According to DIN 7728, ETFE or E/l FE is the international abbreviation for ethylene-tetra-fluorine-ethylene. Figure 6.24 shows the plastic pyramid containing a few weU-known thermoplastics. The pyramid classifies thermoplastics depending on their temperature resistance and costs. ETFE is among the high-performance thermoplastics. 

FIGURE 8.4 Plastic pyramid originally proposed in 1998 by Van der Naald and Thorpe. 

Fig. 19.1 The plastics pyramid according to thermal literature data of common polymers preferred materials for HT-PEM applications are in the upper right region TPI thermoplastic polyimide, PES polyether sulfone, P P)SU poly(phenylene)sulfone, PE E)K polyether(ether) ketone, LCP liquid crystal polymer, e.g., Vectra, PPS polyphenylene sulfide, PTEE polytetrafluoroethylene.

Typical thermoplastic polymers as binders in HT-PEM bipolar plates are polyphenylensulfide (PPS), polyetheretherketone (PEEK), and derivatives of polyphenylsulfone (PSU). Looking at the plastics pyramid (Fig. 19.1), all of these polymers are in the upper right region of high temperature stability and semi-crystallinity. These polymers safely resist the acid and oxygen contact and provide heat deflection temperature far above the operating point of a high temperature PEM fuel cell. 

The plastics pyramid (Fig. 2.8) is a widely accepted mode of graphically presenting the differences between three major subgroups of thermoplastic materials ... 

FIGURE 2.8 Plastics pyramid including worldwide consumption figures... 

Knoop developed an accepted method of measuring abrasive hardness using a diamond indenter of pyramidal shape and forcing it into the material to be evaluated with a fixed, often 100-g, load. The depth of penetration is then determined from the length and width of the indentation produced. Unlike WoodeU s method, Knoop values are static and primarily measure resistance to plastic flow and surface deformation. Variables such as load, temperature, and environment, which affect determination of hardness by the Knoop procedure, have been examined in detail (9). 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

Even in the case of spinal cord injury where application of anti-Nogo antibodies results in regeneration of the cut axons, an additional important element for functional recovery is enhanced fiber growth from the unlesioned fibers, i.e. compensatory plasticity, as discussed above. After high corticospinal tract injury in the rat at the level of the medullary pyramid and treatment with anti-Nogo antibodies, rubrospinal pathways were shown to sprout into deafferented areas of the spinal cord, resulting in high levels of functional recovery, i.e. a functional switch in the remodeled pathway [42]. 

Han JS, Bird GC, Neugebauer V (2004) Enhanced group 111 mGluR-mediated inhibition of pain-related synaptic plasticity in the amygdala. Neuropharmacology 46 918-926 Hansel C, Artola A, Singer W (1996) Different threshold levels of postsynaptic [Ca2-h](i) have to be reached to induce LTP and LTD in neocortical pyramidal cells. J Physiol Paris... 

Davis FI, Squire LR (1984) Protein synthesis and memory a review. Psychol Bull 96 518-559 Deisseroth K, Heist EK, Tsien RW (1998) Translocation of calmodulin to the nucleus supports CREB phosphorylation in hippocampal neurons. Nature 392 198-202 Dinerman J, Dawson TM, Schell MJ, Snowman A, Synder SH (1994) Endothelial nitric oxide synthase localized to hippocampal pyramidal cells implications for synaptic plasticity. Proc Natl Acad Sci U S A 91 4214-4218... 

Lawn et al. (1975, 1978), and Lawn and Marshall (1978) distinguish two types of indenter whose action on the tested surface differs significantly (1) a blunt indenter (e.g., a hard ball) distinguished by an ideal elastic contact, so that the crack initiation is controlled by previously present defects (usually on the sample surface), and (2) a sharp indenter (e.g., a cone or pyramid) distinguished by partially plastic contact, so that the original defects start to grow as the result of the indentation process itself. In practice, the contact situations can therefore be seen as intermediate between the two cases. Within this area all typical indenters used for hardness measurement are contained. 

Comprehensive investigations into brittleness of some crystals determined with a Vickers pyramid led Ikornikova and Khrenova (1951) to establish that crystals of mosaic structure with traces of plastic deformation are more brittle than similar crystals of homogeneous structure. Moreover it has been found (Glazov and Vigdorovich, 1969) that as the mean square displacement of the lattice structural components diminishes, in other words, as the mobility of these components diminishes with propagation of elastic waves, the ultimate effect is increased material brittleness. 

During static hardness tests with plastic materials by observation of the changes in depth of penetration by a ball or pyramid taking place in time at a constant load, two stages of deformation of material are distinguishable ... 

Fig. 6.4.5. Impressions of Vickers pyramid on MgO monocrystal. Cracks around impression made at 973 K indicate growing brittleness of the material. On exceeding 1373 K, impressions exhibit plasticity. (After Tabor, 1965)...

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