Controlling draw resonance during extrusion film casting of nanoclay filled linear low-density polyethylene: An experimental study and numerical linear stability analysis

Abstract

Commercially important extrusion film casting (EFC) processes for manufacturing plastic films or sheets are hampered by several instabilities that severely limits their productivity. In this research we focussed on one important instability: the draw resonance that occurs during the EFC process mainly under extensional flow conditions. Draw resonance is the sustained periodic oscillations in the film dimensions, notably film width and thickness, when the process operates beyond a critical draw ratio (CDR). In this research our goal was to reduce this draw resonance instability by incorporating well dispersed nanoclay fillers in a base polymeric resin (such as a linear low density polyethylene – LLDPE) to determine how these nanocomposite (NC) formulations can prevent or reduce the draw resonance defect. EFC experiments were conducted on the base resin and on the NC formulations under non-isothermal conditions to determine the onset of the draw resonance experimentally. Conventional linear stability analysis was performed to determine the onset of the draw resonance defect numerically. Numerical predictions for the onset of draw resonance were in qualitative agreement with our experimental data. Our results showed that incorporating appropriate nanoclay concentrations in a base polymeric resin indeed enhanced the EFC process stability for those polymer formulations and thus can have important economic implications for processors.

A rheology and processing study on controlling material and process defects in polymer melt extrusion film casting using polymer blends

“…In our previous papers, 28,30,32 our research group has discussed in detail about how viscoelasticity manifested through slow, fast or averaged relaxation modes affect EFC stability. We showed that as the relaxation modes increased, there was a dramatic change in the stability regions.…”

“…We showed that as the relaxation modes increased, there was a dramatic change in the stability regions. In the most recent paper, 32 we demonstrated that it was possible to reduce the draw resonance defect for a linear chain polyethylene such as LLDPE using 2.5 and 5 weight-percent well-dispersed nanclay (NC) fillers. Indeed, our numerical simulations as well as experimental data showed that enhanced melt elacticity for the nanoclay filled LLDPE formulations delayed the onset of draw resonance vis-à-vis the base unfilled LLDPE resin.…”

“…More recently, our group has started work on using various fillers such as organically modified layered silicates (OLMS or nano clays) to control both the necking as well as the draw resonance which take advantage of the better melt elasticity as well as strain hardening in extension for the nanoclay filled PE compositions. 31,32 It is quite well known that industrial polymer processors many times use polymer blends to improve product properties or to ease processing of polymer formulations. In blown film extrusion, for example, several papers have been published that talk about using a long-chain branched polyethylene (LDPE) as a blend component in a linear polyethylene [33][34][35][36][37][38][39][40][41][42] to improve the mechanical properties, enhance rheology and hence bubble stability, improve the lay flat width and reduce film thickness among other properties.…”

“…More recently, our group has started work on using various fillers such as organically modified layered silicates (OLMS or nano clays) to control both the necking as well as the draw resonance which take advantage of the better melt elasticity as well as strain hardening in extension for the nanoclay filled PE compositions. 31,32…”

A review of current knowledge and future trends in polymer/boehmite nanocomposites

“…[6][7][8] Boehmite consists of aluminum oxide hydroxide nanoparticles. 9 Boehmite also has hydroxyl groups on the surface. Boehmite has important features such as transparency, mechanical strength, chemical resistance, and corrosion inhibition.…”