Polymer Engineering and Science articles from March 2002

Polymer Engineering and Science archives from March 2002

A theoretical approach to solid filler dispersion in a twin-screw extruder.(Abstract)
March 1, 2002... INTRODUCTION In the polymer industry, mineral particles are often used to improve material properties and to reduce cost. The compounding step, usually performed using co-rotating twin-screw extruders, must ensure a correct dispersion of...

Gross melt fracture of polyethylene. I: A criterion based on tensile stress.
March 1, 2002... INTRODUCTION In polymer extrusion, several types of extrudate distortion are observed as the extrusion rate is increased. Surface melt fracture (SMF), or sharkskin, is observed at moderate extrusion rates in some polymers and is...

Gross melt fracture of polyethylene. II: Effects of molecular structure.
March 1, 2002... INTRODUCTION At the present time there is no clear understanding the effect of molecular structure on GMF, although it is generally agreed that broadening the molecular weight distribution (MWD) and decreasing the molecular weight reduce...

Combined effect of temperature and thickness on work of fracture parameters of unplasticized PVC film.
March 1, 2002... INTRODUCTION The fracture behavior of brittle materials can be easily characterized using the Linear Elastic Fracture Mechanics (LEFM) approach. For brittle and semi-brittle materials, which exhibit small-scale crack-tip plasticity, an...

Development of a curvilinear viscoelastic constitutive relationship for time dependent materials. Part A: Theoretical discussion.
March 1, 2002... INTRODUCTION Materials such as polymers (plastics) are complicated viscoelastic materials, the stress and strain of which are not easily related to each other. Much has been done relating stress and strain in a small deformation context....

Example problems.(Development of a curvilinear viscoelastic constitutive relationship for time-dependent materials, part B)(Statistical Data Included)
March 1, 2002... INTRODUCTION Part A of this work discussed in detail a rheological constitutive model to describe the stress and strain behavior of time dependent materials (1). Part B explains the results of some example problems solved using the...

Experimental.(Hot embossing in microfabrication, part 1)(Statistical Data Included)
March 1, 2002... INTRODUCTION In recent years, many polymer-based micro- and nano-fabrication techniques have been explored for applications in bio- and chemical-MEMS (Micro Electro Mechanical Systems) (1). Polymer-based materials offer a wide range of...

Rheological characterization and process analysis.(Hot embossing in microfabrication, part 2)(Statistical Data Included)
March 1, 2002... INTRODUCTION The rheological behavior of polymers at temperatures far below and well above the glass transition temperature ([T.sub.g]) has been widely studied. At temperatures far below [T.sub.g], the uniaxial tensile test is the most...

Effect of curing temperature on the morphology of unsaturated polyester resin blended with Poly(vinyl acetate).(Statistical Data Included)
March 1, 2002... INTRODUCTION Low-profile additives (LPAs) are used in unsaturated polyester/styrene (UPE/styrene) resin formulations to improve the surface of molding compounds, compensating for resin shrinkage. Poly(vinyl acetate) (PVAc) is widely used...

Experimental investigation of the cure-dependent response of vinyl ester resin.(Statistical Data Included)(Abstract)
March 1, 2002... INTRODUCTION Fiber-reinforced composites have enjoyed widespread use because the combined characteristics of the reinforcement and matrix generally provide a structure with high strength and relatively low weight. One of the common...

The Payne effect for particle-reinforced elastomers.(Statistical Data Included)
March 1, 2002... 1 INTRODUCTION This paper is concerned with the Payne effect (1-4): a noticeable decrease in the storage modulus of filled rubbery polymers with an increase in the amplitude of small-strain oscillations in dynamic mechanical tests. Changes...

Effect of graft ratio on the dynamic moduli of Acrylonitrile-Butadiene-Styrene Copolymer.(Statistical Data Included)
March 1, 2002... INTRODUCTION ABS (Acrylonitrile-Butadiene-Styrene copolymer) has long been used commercially, and has been studied in depth for many years. It consists of three major components, but it forms a binary phase system that consists of graft...

Critical conditions for unstable flow.(Flow through a convergence, part 1)(Statistical Data Included)
March 1, 2002... INTRODUCTION Unstable flow is a problem often encountered in polymer processing, where anomalies in the appearance of the extrudate, or oscillations in flow and pressure are observed after a critical flow rate. Tordella was the first to...

Mixing of high viscosity ratio polymer blends.(Flow through a convergence, part 2)(Statistical Data Included)
March 1, 2002... INTRODUCTION The polymer industry is continuously searching for new methods to improve the properties of existing materials, especially superior mechanical properties. Increasing the average molecular weight of a given polymer usually...

The flow of polymer melts through the clearance over a barrier flight in extruders.(Statistical Data Included)
March 1, 2002... INTRODUCTION It has been well established that the performance of an extruder can be greatly improved by using an appropriate high performance screw and optimizing the special screw geometry (1-5). Most high performance screws incorporate...