Modulus changes additives/ particles

Stretching a polymer sample tends to orient chain segments and thereby facilitate crystallization. The incorporation of different polymer chains into small patches of crystallinity is equivalent to additional crosslinking and changes the modulus accordingly. Likewise, the presence of finely subdivided solid particles, such as carbon black in rubber, reinforces the polymer in a way that imitates the effect of crystallites. Spontaneous crystal formation and reinforcement... 

To illustrate how the effect of the adsorption on the modulus of the filled gel may be modelled we consider the interaction of the same HEUR polymer as described above but in this case filled with poly(ethylmetha-crylate) latex particles. In this case the particle surface is not so hydrophobic but adsorption of the poly (ethylene oxide) backbone is possible. Note that if a terminal hydrophobe of a chain is detached from a micellar cluster and is adsorbed onto the surface, there is no net change in the number of network links and hence the only change in modulus would be due to the volume fraction of the filler. It is only if the backbone is adsorbed that an increase in the number density of network links is produced. As the particles are relatively large compared to the chain dimensions, each adsorption site leads to one additional link. The situation is shown schematically in Figure 2.13. If the number density of additional network links is JVL, we may now write the relative modulus Gr — G/Gf as... 

Ways to increase membrane durability have been examined by various researchers across the country. Maurtiz et al. examined the use of metal-oxide metal particles to increase the properties of the membrane. A titanium isopropoxide (Figure 11.4) addition to Nation membranes generates quasi-network particles this improves membrane modulus and dimensional stability [17], In addition, the titanium matrix reduces fuel crossover and minimizes chemical degradation. Table 11.2 shows the increase in modulus along with stress and strain and stress changes after the addition of the titanium matrix [17], With a 20% load of the titanium matrix, performance criteria remain comparable. Acid functionality remains intact however, water uptake is reduced as volume inside clusters is occupied. Conductivity is reduced due to chain mobility [17],... 

The change induced in the stress-strain behavior by incorporation of elastomeric particles into a PS matrix has been reported [15]. On toughening, PS brittle behavior changes into ductile with flow. The rubber-modifled polymer absorbs considerably more energy thus, higher elongation to break can be achieved. By contrast, an addition of rigid resin to a ductile polymer enhances the modulus and the heat deflection temperature. 

Polymers such as EVA, are used as admixture because it modify the elastic modulus, toughness, permeability and bond strength to various substrates in cement and mortars [10]. The polymer forms a film that creates a network inside the cement matrix, partially covering hydrated and anhydrous cement particles, sealing pores and bridging microcracks. Besides, this addition also changes the hydration rate. Silva et al [11] compare the effects of two polymers a water soluble polymer (HPMC — hydroxypropylmethylcellulose) and a latex [EVA-poly(ethylene-co-vinyl acetate)] on... 

A careful reading of the literature [coupled, in this case, with experimental work (Manson and Chiu, 1973a)] reveals that both small and large filler particles can induce significant changes in phenomena such as sorption, permeability, or relaxation behavior of the matrix (notably in the glass transition temperature Tg and in damping characteristics, E" or tan 5), in addition to the noninteractive increases in modulus predicted by relationships such as Kerner s equation (12.3). The fact that some exceptions and contradictions continue to exist serves to stimulate further study rather than to deny the tendency toward filler-matrix interaction. Typical evidence may now be summarized. 

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