Melt modulus

Various workers [2, 7] suggested that increasing either gel content (above 50%, which is typical for foam manufactures) or melt modulus results in increased in foam density. Figures 15.1 and 15.2 for systems containing DCP alone and in the... 

Fig. 15.1 Effect of gel content and melt modulus on foam density (1808)...

Fig. 15.2 Dependence of foam density on gel content and melt modulus for samples containing varying concentrations of DCP and a TAG concentration fixed at 0.5 phr...

Figure 15.5 gives a wealth of information. It is important to understand that each series of three separate results at each nominal gel content represents an adjustment in DCP concentration to give the nominal gel content in the presence of 0, 0.5 and 2.0 phr TAC (increasing TAC concentration produces progressive increase in melt modulus and foam density). Result positively indicates that gel content is not a suitable indicator to predict foam density (as previously suggested). However, if all... 

Fig. 15.4 The effect of formulation on melt modulus at similar gel content...

Fig. 15.5 The dependence of foam density on melt modulus at specific gel contents (DCP, TAG ratios [phr] shown in parentheses)...

The effects of formulations containing similar gel content on swell ratio are shown in Fig. 15.6. The results show that at ary specific gel content, the swell ratio reduces with increasing TAC concentration. This confirms the earlier hypothesis that higher TAC concentrations in the crosslinking system produce higher crosshnk density. The results are also in accordance with melt properties where the higher the TAC concentration, the higher the melt modulus. 

Fig. 15.8). There is a positive indieation that all data points may approximate to a mastereurve more eonelusively than those seen with melt modulus results (Fig. 15.5). The results suggested that swell ratio (itself related to crosslink density) might be a useM parameter upon which to base prediction of foaming behaviour. 

When foaming traditional DCP/LDPE systems, the foam density appeared to be controlled by gel content and/or the melt modulus (above 50% gel fraction). It was concluded that either gel content or melt modulus was inadequate to define foaming behaviour when TAG is included in the crosshnking system. Moreover, that swell ratio (crosslink density related) was a more universal parameter to predict foaming behaviour than either gel content or melt modulus independent of formulation. 

The influence of adding polyfunctional monomers having different structures and functionality into a dicumyl peroxide-based crosslinking system for LDPE was investigated. Monomers employed were diallyl phthalate, trimethylolpropane trimethacrylate and triallyl cyanurate. The effects of formulation on matrix gel content and on foam density at similar gel content were examined and the dependence of foam density on melt modulus assessed. The applicability of swell ratio for estimating foam density was evaluated and the suitability of triallyl cyanurate as a crosslinking promoter for LDPE foam demonstrated. 20 refs. 

Fig. 15.8). There is a positive indication that all data points may approximate to a mastercurve more conclusively than those seen with melt modulus results (Fig. 

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