S. N. Bhattacharya

Melt Strength and Elastic Behaviour of LLDPE/LDPE Blends

Abstract Differences in processability between linear low denisty polyethylene (LLDPE) and low density polyethylene (LDPE) as well as for their blends subjected to extensional flow were assessed in terms of melt strength and elastic parameters from shear flow such as storage modulus (G′), and first normal stress difference (N11 – N22). The results revealed similar synergistic effects for these parameters in the LDPE rich blends. A DSC test carried out on these LLDPE/LDPE blends when fast cooled disclosed the existence of two phases in the molten blends for the same composition range where the melt strength synergism was observed. The results are discussed in terms of the influence of the different molecular structures of the blend polymers and their miscibility on the measured melt strength. A mechanism is suggested to explain the observed synergistic phenomenon.

Synthesis and Characterisation of Branched Poly(ethylene terephthalate)

Branched poly(ethylene terephthalate)s (PET) were synthesised with a variety of molar masses and with a large range of degree of branching by introduction of mono-, tri-(glycerol) and tetra-functional (pentaerythritol) comonomers to dimethyl terephthalate and ethylene glycol. The monofunctional alcohols, dodecanol and benzyl alcohol, were used as terminating agents to minimise gelation. The effect of various reaction parameters, such as percentage glycerol or pentaerythritol and polymerisation time, on limiting viscosity number [η] and weight average molar mass (Mw) were investigated. The thermal behaviour of branched PET was studied by differential scanning calorimetry; all samples showed a characteristic double endothermic melting peak and the glass transition temperature was not observed. Some branched PETs were subjected to solid-state polymerisation to increase the molar mass of previously prepared branched polymers. The solid-state polymerisation technique showed that the process not only promoted the molar mass but, more importantly, it increased the crystallinity of the polymer. Overall, the solid-state reaction rate was governed by initial molar mass, crystallinity, reaction temperature and time.

Rheological Behaviour of LLDPE/ LDPE Blends under Elongational Deformation

Abstract Blends made of one linear low density polyethylene (LLDPE) and either of two low density polyethylenes (LDPE 1 and LDPE 2) were tested in elongational modes of deformation using elongational viscosity and melt strength test. In addition to rheological measurements the melt miscibility of the blends was ascertained by the differential scanning calorimetry (DSC) test on melt quenched samples. From the results, the relation between melt morphology of the blends and their performance under elongation, as well as the influence of molecular structure in particular long chain branching, on elongational response were determined. It was observed that high resistance to elongational deformation of the blends is linked to the immiscibility of the blend components in the melt. On the other hand the influence of long chain branching is to increase elongational viscosity for the parent polymers, as well as promoting the blend immiscibility and therefore altering elongational performance of the blends.

Liquid crystalline polymers: molecular simulation of some polyethers containing oxetanic rings in the main chain

Abstract This paper presents a conformational analysis of some polyethers containing the oxetanic ring in the main chain. The studied polymers were synthesized by phase transfer catalysis, using 3,3-bis(chloromethyl)-oxetane and various bisphenols. The analysis was performed using the Cerius 2 program (version 2.0) molecular simulation software for material science, designed by Molecular Simulations Incorporated (MSI). This study tries to elucidate some aspects concerning the difficulties appearing in the liquid crystalline propertys characterization. These difficulties are induced by the cross-linking processes that take place in certain situations due to the opening of the oxetanic rings at high temperature.

Dynamic rheology of branched poly(ethylene terephthalate)

Branched poly(ethylene terephthalate)s (BPET) of varying molar mass have been synthesized with glycerol and pentaerythritol as branching comonomers, and their rheological behaviour has been measured. In this study, we describe the use of dynamic and steady shear measurements to examine the influence of the proportion and type of branching comonomers on the melt viscosity of BPET. Steady shear rheology has been used to measure the shear rate dependence on the apparent viscosity. Dynamic (oscillatory) measurements have been used to obtain the complex viscosity η* (ω) and the storage modulus G′ (ω) as a function of frequency. n n n nG′ (ω) represents the elastic component of the viscoelastic melt; this variable was measured as a function of frequency at various temperatures in the linear viscoelastic domain. Linear poly(ethylene terephthalate) (LPET) exhibited nearly Newtonian behaviour, while BPET became shear thinning at relatively low shear rates. The viscosity and elasticity increased with increase in molar mass and specific branching composition. This was attributed to increasing chain entanglements at higher molar mass and to increasing branching of the BPET. At higher shear rates or frequencies, the BPET show much greater shear thinning character than LPET and this is more pronounced with higher branching proportions. n n n n© 2000 Society of Chemical Industry

Temperature Rise in the Extrusion of Highly Viscous Composite Materials

Abstract In this paper a model has been developed for the approximate evaluation of the temperature rise in the extrusion of filled plastic materials. The model developed in this paper considers the influence of thermal and rheological properties of extrudate, operating conditions of extrusion and geometry of screw channel on the temperature of extrudate. The optimal parameters of screw channel in terms of productivity and temperature build-up are discussed. The model was tested by experimental studies in which filled plastic material was produced using ground rubber tyre particles dispersed in LDPE. The agreement between the model prediction and the experimental data is discussed.

Rheological Behaviour of LLDPE/LDPE Blends under Elongational Deformation: Effect of Temperature

Abstract The effect of temperature on the rheological response under elongation of two low density polyethylenes (LDPE 1 and LDPE 2), linear low density polyethylene (LLDPE) and their blends of different compositions was observed by using a constant strain rate elongational rheometer. In addition, blends were tested in the oscillatory shear test, and the data measured at 160, 190, and 230°C indicate the larger level of intermolecular interactions in a blend than in the pure polymers. Elongational viscosity measured at temperatures of 140, 150, 170 and 180°C revealed a much greater sensitivity for LLDPE (greater strain hardening with increasing temperature) to changing tenperature than is observed for LDPE. This observatuion, coupled with the effect of melt morphology on elongational rheology, has been used to explain the synergism in elongational viscosity exhibited by LDP-E-rich blends.