Non‐linear rheological response as a tool for assessing dispersion in polypropylene/polycaprolactone/clay nanocomposites and blends made with sub‐critical gas‐assisted processing

Abstract

Polypropylene (PP) was blended with polycaprolactone (PCL) and nanoclay (NC) in a twin‐screw extruder (TSE) using a traditional extrusion process and a sub‐critical gas‐assisted process (SGAP). SGAP is a new and facile processing method that injects compressed gas (CO2 or N2) at low pressures (~10 bars) into the barrel of the extruder to induce rapid and repetitive foaming and resolubilization as the melt travels through regions of high pressure and low pressure. Bubble expansion during foaming introduces an equibiaxial elongational flow not otherwise generated in TSE, adding to the total stress the polymer matrix can exert to break up nanoparticle agglomerates and reduce the droplet size of secondary polymers in blends. Impact, morphology, and X‐ray diffraction (XRD) properties confirmed a smaller PCL phase droplet size and an increase in dispersion of the NC when SGAP was used. Standard small amplitude oscillatory (SAOS) rheological tests for the storage modulus G′ were not sensitive enough to discern the difference between the traditionally extruded samples and the SGAP samples. However, the zero‐strain non‐linearity parameter, Q0, determined by the Fourier‐Transform rheology, was able to distinguish the enhanced dispersive and mixing capabilities of SGAP. Practical implications of SGAP and Fourier‐Transform (FT) rheology are also discussed in this paper. POLYM. ENG. SCI., 60:55–60, 2020. © 2019 Society of Plastics Engineers

Viscoelastic Rheological Behaviors of Polypropylene and LMPP Blends

“…The spherulite shape and size are the obvious characteristics [39]. Spherulitic growth rate is related to the crystallization temperature and is nonlinear in non-isothermal conditions of the polymeric blends.…”

Research on improved gas‐assisted extrusion of plastic sheets based on time–temperature equivalence principle

“…In conventional plastic sheet extrusion, the high viscoelasticity of polymers makes them susceptible to undesirable extrudate swell [1][2][3] and tensile deformation, [4][5][6][7][8][9] and the internal stress in the product also damages its serviceability. [10][11][12][13] Gas-assisted extrusion (GAE) [14][15][16][17][18][19] technology improves or eliminates the defects [20][21][22] encountered during conventional extrusion by forming a thin and stable gas layer around the polymer melt and between the inner walls of the die.…”

Formation of uniform polymer assembly with silica nano‐sol‐supported metallocene catalysts in a stirred‐tank reactor

“…In order to meet the specific requirements for commercial applications, PP properties have been improved via compounding or blending with a variety of additives. [ 2 ] In addition, PP products can be optically transparent using a variety of processing approaches. [ 3 ] Typically, PP is manufactured in a continuous slurry reactor or in a gas‐fluidized bed reactor using Ziegler‐Natta catalysts supported on MgCl 2 , which have non‐uniform active sites and thus produce polymer with wide molecular weight distribution (MWD).…”