Unlike most published polymer processing and/or forming research,the transformation of polyolefins to fabricated articles often involves non-confined flow or so-called free surface flow(e.g.fiber spinning,blown films,and cast films)in which elongational flow takes place during a fabrication process.Obviously,the characterization and validation of extensional Theological parameters and their use to develop Theological constitutive models are the focus of polyolefins materials transformation research.Unfortunately,there are challenges that remain with limited validation for non-linear,non-isothermal constitutive models for polyolefins.Further complexity arises in the transformation of polyolefins in the elongational flow system as it involves stress-induced crystallization process.The complicated nature of elongational,non-linear rheology and non-isothermal crystallization kinetics make the development of numerical methods very challenging for the polyolefins materials forming modeling.From the product based company standpoint,the challenges of materials transformation research go beyond elongational rheology,crystallization kinetics and its numerical modeling.In order to make models useful for the polyolefin industry,it is critical to develop links between molecular parameters to both equipment and materials forming parameters.The recent advances in the constrained geometry catalysis and materials sciences understanding(INSITE* technology and molecular design capability)has made industrial polyolefinic materials forming modeling more viable due to the fact that the molecular structure of the polymer can be well predicted and controlled during the polymerization.In this paper,we will discuss interrelationship(models)among molecular parameters such as polymer molecular weight(Mw),molecular weight distribution(MWD),long chain branching(LCB),short chain branching(SCB or comonomer types and distribution)and their affects on shear and elongational rheologies,on tie-molecules probabilities,on non-isothermal stress-induced crystallization,on crystalline/amorphous orientation vs.mechanical property relationship,etc.All of the above mentioned inter-relationships(models)are critical to the successful development of a knowledge based industrial model.Dow Polyolefins and Elastomers business is one of the world largest polyolefins resin producers with the most advanced INSITE* technology and a"6-Day model"molecular design capability.Dow also offers one of the broadest polyolefinic product ranges and applications to the market.
展开▼
