Repolymerization effect

Table 5.3, extracted from the European Patent application repolymerization [28], shows the beneficial effects of titanates on most properties of ABS, PC, PP, and PS thermoplastics. As an additional example. Figure 5.6 shows the repolymerization effect of 0.2% LICA 12 on a 50/50 blend of LDPE and PP after six thermal cycles through a twin-screw extruder. The melt index of the control blend without titanate climbs from 17 to 38, while the value for the blend with titanate is only 24 this indicates a significant decrease in chain-scission due to the titanate. 

Table 5.3 Repolymerization effect of various neoalkoxy titanates and zirconates on the mechanical properties of unfilled ABS, PC, PP, and PS thermoplastics.

The caprolactam obtained must meet die specifications of permanganate number, volatile bases, hazen color, UV transmittance, solidification point, and turbidity in order to be used for repolymerization alone or in combination witii virgin CL.5 Reported CL purification methods include recrystallization, solvent extraction, and fractional distillation. One solvent extraction technique involves membrane solvent extraction. Ion exchange resins have been shown to be effective in the purification of aqueous caprolactam solutions. In one such process,... 

In view of the possibility of random free-radical scission of some covalent bonds, despite a great deal of dissipation of energy in the same sample, this repolymerization may be the likely interpretation, as the effect could result from recombination (or rather free-radical condensation) in the compressed material. 

Heterogeneous tar reactions on the surfaces of (partially) reacted biomass, char particles etc. The same types of reactions as in the homogeneous case (cracking, oxidation, repolymerization) may occur but the surfaces may have a catalytic effect on the reactions. 

At the high molecular weight end the theoretical curve lies below the experimental one. The present theory does not consider chain transfer and repolymerization ( 5) which must occur to some degree. For small amounts of chain transfer, the effect of repoly-merizatlon is to generate a high molecular weight tail on the initial distribution, which can be seen here. 

Recently, another role for ABA-cytoskeleton interactions was discovered in guard cells of Vida faba leaves [150]. ABA specifically disrupted the MTs in guard cells but not in other epidermal cells. This effect resulted in the closure of stomata. When MTs repolymerized, the stomata reopened. Interestingly, no other plant hormone could elicit such a response in the guard cells. Actually, a role for MTs in the stomata closure-opening mechanism had been proposed earlier on the grounds that the MT-disrupter, colchicine, inhibited stomatal opening in Tradescantia leaves [151]. 

Some new technology is being developed by which mixed plastics may be depolymerized at high temperatures into monomers that pan be easily separated and repolymerized. Pyrolysis is also effected on commingled plastics, as well as on thermosets, wherein the product consists of a fuel, that will be used for energy. In summary, the concept of tertiary recycling may be practical for some polymers while also effective for better recycling of mixed plastics or thermosets. 

For safe disposal of the products without any adverse effects to the environment, such as recycling and subsequent repolymerization, recycling to olefinic feedstock by pyrolysis, continued burial in landfill sites, incineration, and use of environmentally degradable polymers... 

Minor amounts of thermally stable neoalkoxy titanate and zirconate additives may provide a means for postreactor, in situ metallocene-like repolymerization catalysis of a filled or unfilled polymer during the plasticization phase. This may result in the creation of metallocene-like (titanocene or zirconocene) behavior associated with effects such as increased composite strain to failure resulting in increased impact toughness or enhanced polymer foamabUity. Other effects to be discussed below with specific examples are related to enhanced processability, reduced polymer chain scission, shortened polymer recrystallization time, and compatibilization of dissimilar polymers. 

Repolymerization is a patented [28] concept by the author to explain new and novel rheology and stress/strain effects in thermoplastics and thermosets obtained with... 

Ma et al. ascribed a dual role to the catalyst, with the acid sites converting the depolymerized intermediates into desirable and more stable products while the catalyst surface prevents repolymerization and coke formation (Scheme 10) [305], A high catalyst-to-substrate ratio was shown to increase the liquid product yield. They also studied the effect of the Si/Al ratio and the acidity of the catalyst. Decreasing the silica-to-alumina ratio and thus increasing the amount of acid sites of ZSM-5 increased the production of aromatics. ZSM-5 with an intermediate siUca-to-alumina ratio showed the highest phenols production (14 wt% of the Uquid product). This was in line with the results of Li et al. [303]. 

The force which propels secretory granules along the microtubules is less clear. It is known that the micro tubular system exists in at least two states the fully polymerized form represented by intact microtubules, and the disintegrated form represented by a pool of depolymer-ized globular proteins (tubulin) in the cytoplasm. In order for microtubules to function properly, a dynamic state of equilibrium must exist between the fully-formed tubules and the tubule constituent pool. Thus, colchicine and other antimitotic agents bind to specific sites on the microtubular subunits. It has been proposed that they exert their effect by inactivating the free subunits and thereby shift the equilibrium between the associated and dissociated states of the microtubules so that eventually no intact microtubules remain and secretion is inhibited. Similarly, stabilization of microtubules in the polymerized form with D2O also inhibits cellular secretion of insulin. From this, one can hypothesize that if the secretory vesicles were somehow attached to the microtubules, possibly by way of microfilaments, a constant cycle of depolymerization near the cell periphery, with a repolymerization at the central area of the cell, would advance the secretory vesicle from the cell center to the cell web. In addition, if tubulin actually contains an actin-like contractile protein, then this contractile property may well contribute to the intracellular movement of secretory materials. 

Staroszczyk, H., Fiedorowicz, M., Janas, P. Tomasik, P. (2007). Effect of the red and green linearly polarized Ught upon polysaccharide depolymerization-repolymerization in starch granules. Polimery, 52(11 12), 63-70. 

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