Crosslink effect

Crosslinked xanthan gums have also been used to reduce the permeability of thief zones. Trivalent chromium and aluminum have been used as crosslinkers (223,224). While crosslinker effectiveness is reduced at high salinity, Cr(III) has been used in the field at... 

The coagent functionality of this compound helps to improve the crosslinking effect, and is comparable with DCP. Moreover, the multifunctional peroxides investigated provide by-products after their decomposition, but without an unpleasant smell, unlike DCP. Comparative physical properties of the PP/EPDM TPVs... 

These relationships show that (i) if the copolymer approach is considered as a correct model, this means that the Fox-Loshaek relationship is only valid at low crosslink densities (as effectively found experimentally) (ii) The Fox-Loshaek constant is an increasing function of Tgi, e.g., of the chain stiffness, as effectively found. KFl varies from 6-10 K kg mol-1 for fully aliphatic to 50-60 K kg mol-1 for highly aromatic systems. Thus, it appears that both chain stiffness and crosslinking effects cannot be considered independent. The effect of crosslinking, represented for instance by (Tg—Tgi) in the Fox-Loshaek equation, is an increasing function of the chain stiffness. This dependence is taken into account in the approach based on the theory of conformational entropy (Di Marzio, 1964) and leads to... 

It was initially stated that Cf are Cf were universal constants (Cf 17 Cf 50 K), but Cf can vary between 2 and 50 and Cf between 14 and 250 K (Mark, 1996). Epoxy values have been found in the low part of these intervals Cf 10, Cf 40 15 K (Gerard et al., 1991), whereas unsaturated polyester values can be relatively high Cf/Cf = 15-55 = 73-267 K (Shibayama and Suzuki, 1965). There is, to our knowledge, no synthetic study on the ideality and crosslinking effects on Cfand Cf. The time-temperature equivalence principles will be examined in detail in Chapter 11, which is devoted to elasticity and viscoelasticity. 

In the glass transition region, both structural scales play a significant role and their effects cannot be dissociated. The crosslinking effect (macro-molecular scale) on Tg, is an increasing function of the chain stiffness, which is under the dependence of molecular scale factors (essentially aromaticity). 

Exclusively mechanically interlocked linear polymer blends, typically, are not thermodynamically phase stable. Given sufficient thermal energy (Tuse>Tg), molecular motion will cause disentanglement of the chains and demixing to occur. To avoid phase separation, crosslinking of one or both components results in the formation of a semi-IPN or full-IPN, respectively. Crosslinking effectively slows or stops polymer molecular diffusion and halts the phase decomposition process. 

R. Leboda, B. Charmas, S. Chodorowski, J. Skubiszewska-Zifba, and V. M. Gun ko, Carbon-Mineral Adsorbents Prepared from Spent Palygorskite - Crosslinking Effect, Microporous and Mesoporous Materials, in press. 

Each carbonized material is characterized by the size and distribution of the pores. We have found it convenient to distinguish between large pores (> 2000 A) and smaller ones with sizes down to 50 A. Furthermore, the pore size depends on the chemical composition of the material. The smallest pores are due to the crosslinking effects of some heteroatoms (such as oxygen and sulfur) or to the effect of defects such as tetrahedral bonds, etc., which reduce BSU mobility during the soft stage. As the... 

The 12 investigations compiled here deal mostly with functional investigations in the food area. Three chapters discuss soy proteins, relating the effects of heat, specific solvents, and enzyme activity on structure and functional properties. Single chapters are concerned with the proteins of wheat, milk, and yeast, respectively, as well as specific crosslinking effects and, enzyme-carrier interactions. Other chapters contrast general functional properties of different proteins. 

In this work we used polystyrene-based ionomers.-Since there is no crystallinity in this type of ionomer, only the effect of ionic interactions has been observed. Eisenberg et al. reported that for styrene-methacrylic acid ionomers, the position of the high inflection point in the stress relaxation master curve could be approximately predicted from the classical theory of rubber elasticity, assuming that each ion pah-acts as a crosslink up to ca. 6 mol %. Above 6 mol %, the deviation of data points from the calculated curve is very large. For sulfonated polystyrene ionomers, the inflection point in stress relaxation master curves and the rubbery plateau region in dynamic mechanical data seemed to follow the classical rubber theory at low ion content. Therefore, it is generally concluded that polystyrene-based ionomers with low ion content show a crosslinking effect due to multiplet formation. More... 

The blends (PET plus core-shell elastomers) were compounded using a co-rotating twin screw extruder. The contains of particules ranged from 7 to 21 % in mass. Test bars were injection moulded in a second step. In order to produce compound of different levels of crystallisation, the mould wall temperature was varied. Truly amorphous mouldings could not be obtained. However, for mould temperature of 5°C only a small amount (less than 8 %) of crystalline phase was observed. These mouldings will be considered as amorphous, since their continuous phase is amorphous. Conversely, a wall temperature of 145°C made it possible to reach the maximum level of crystallisation (approximately 30 % in mass). Finally, no evidence for a significant crosslinking effect due to reactive nodules was found. 

Topological effect caused by topological constraints introduced by crosslinks on the properties. This effect is referred to simply as the "crosslinking effect" by many authors. 

Diffusion in Semicrystalline Polymers. The extension of the simple two phase model to include the diffusion coefficient in semicrystalline polymers requires some refinements. Given the tensorial character of the diffusion processes, one must first consider the spatial organization of the dispersed impermeable phase. Second, one might, also, expect that the "crosslinking" effect from tie molecules between crystallites and other chains merely anchored to the crystal would reduce the mobility of the amorphous phase. Both issues have been the focus of numerous investigations (19-29). 

When a sample of elastomer is stretched, it becomes anisotropic in that the network chains tend to orient themselves more in the direction of stretch than in the lateral directions. The more ordered chains favor the formation of crystallites. These crystallites will tie together a number of neighboring network chains, thereby exerting an additional crosslinking effect. This increase in the degree of crosslinking will in turn cause a rise in the elastic stress. The reason that these crystallites in fact act as crosslinks is attributable... 

Each of these repeating units is connected on two places via the crosslinks with the other molecule chains. The Tg-value of this system can considered to be the sum of the Tg-value of a linear polymer with the above given repeating unit and a crosslinking effect. The Tg-value contribution can be calculated using the modified cohesion energy method with the n i 4 0Ecoh. values from Table 7.1 ... 

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