Rheological aspects and film processability of poly (lactic acid)/linear low‐density polyethylene blends

Abstract

Poly (lactic acid) (PLA) and Linear low‐density polyethylene (LLDPE) were compounded in a corotating twin screw extruder. PE‐g‐glycidyl methacrylate was also added as a reactive compatibilizer in PLA/LLDPE blend system, which lowered interfacial tension between PLA and LLDPE. Blown films were prepared by using a single‐screw extruder for all compounded blends. The investigation of the rheological properties of a polymeric system is very important to study the processability and understand structure‐property relationship in blown films. In the present research work, the rheological properties have been investigated to assess the processability of blown films of PLA/LLDPE blends. Oscillatory shear rheology viscoelastic spectra showed an increase in the storage and loss moduli with the increase in LLDPE and compatibilizer content, which indicated pronounced viscoelastic behavior of PLA with the addition of LLDPE and compatibilizer. A steady increase in the value of extensional viscosity as a function of time was observed with the addition of LLDPE and compatibilizer in PLA. The blends with higher LLDPE content exhibited much more prominent strain hardening characteristics than those with lower LLDPE content.

Role of Rheology in Morphology Development and Advanced Processing of Thermoplastic Polymer Materials: A Review

“…The difference between the bubble stabilities of the different grades of PE was ascribed to the difference between the strain hardening behaviors of these materials. The dependence of bubble stability on the strain hardening and melt strength of the polymeric material has been demonstrated by other researchers. ,− Moreover, strain hardening leads to films with higher uniformities in thickness, that is, lower inhomogeneity indices. ,, …”

“…The bubble is cooled and vertically pulled via collapsible guides and nip rolls, where it is flattened. The layflat film is pulled downward over a deflection pulley via drive rolls and is taken up by the winder while maintaining a uniform takeoff speed. , A typical blown film extrusion line is depicted in Figure .…”

“…In film blowing, the blow-up ratio (BUR), draw-down ratio (DDR), take-up ratio (TUR), and inhomogeneity index ( r ) are presented by eqs , , , and , respectively: normalB normalU normalR = normalb normalu normalb normalb normall normale .25em normald normali normala normalm normale normalt normale normalr normald normali normale .25em normald normali normala normalm normale normalt normale normalr normalD normalD normalR = normald normali normale .25em normalg normala normalp normalf normali normall normalm .25em normalt normalh normali normalc normalk normaln normale normals normals × normalB normalU normalR normalT normalU normalR = v v 0 r = S h normala normalv where v is the velocity of the take-up roll, v 0 is the melt velocity at the die exit, h av is the average film thickness, and S is the standard deviation. Lower r values indicate the presence of highly homogeneous films. , …”

“…In their investigations on various grades of PE, Fang et al noticed that higher elasticity (namely, higher G ′) resulted in higher bubble stability. Furthermore, in their studies on PLA/LLDPE blends, Singh et al have reported the role of higher G ′ in the enhancement of bubble stability. The importance of both extensional and dynamic rheologies in film blowing has been highlighted by many researchers. ,,− …”

A Novel Mandrel-Free Blown Film Die with Ultrashort Flow Distance and Uniform Discharge: Theoretical Modeling and Simulation

“…At the same time, as the melt flows around the fins or wing supports and reunites, these indispensable mandrel bracket will produce many weld seams in the die. The spiral die contains multiple small flow channels, which can avoid the problem of weld seams, − but complex and narrow multiple flow channels will greatly extend the residence time of melts in the die and aggravate the thermal decomposition of polymer melts…”