Ph. D. Candidate:Guangming Li Supervisor:Prof. Chul B. Park Study of the Solubility of Gas in a Polymer Melt & Cell Nucleation in Die Microcellular Plastics Manufacturing Laboratory, University of Toronto

Outline Introduction Objectives Background Approach Experiments Contributions

Introduction

Plastic Foams Plastic foams Decreased density Cellular structure Advantages over non-foamed plastic Insulating properties Impact resistant characteristics Buoyancy Outstanding strength-to-weight ratios

Plastic Foam Processing Formation of single-phase polymer/gas solution Cell nucleation Cell growth Stabilization Two system + gas polymer Two-phase polymer/gas mixture Single- phase polymer/gas solution Gas injectionMixing & diffusion Diffusion

Plastic Foam Processing Formation of single-phase polymer/gas solution Cell nucleation Cell growth Stabilization Distance P solubility Die Pressure

Objectives

To systematically investigate the gas solubility for different polymer/gas mixture systems To verify the solubility pressure inside the die during the continuous plastic foaming process

Background

Pressure Decay + SL-EOS Y. Sato, etc., Fluid Phase Equilibria 162 (1999) 261; for N 2 and CO 2 in PP, HDPE and PS Electrobalance + Partial Volume by Henrian Sorption Theory B. Wong, etc., Journal of Polymer Science (Part B) 36 (1998) 2025; for PS + CO 2 and PVC + CO 2 Previous Study of Solubility

Application of Gas Solubility in an Extrusion Die PRESSURE VOLUME Isotherm Critical Point Saturated Vapor (Binodal) Liquid Spinodal Vapor Spinodal Saturated Liquid

The minimum work to create a bubble (radius R) The bubble nucleation rate

Approach

Theoretical Prediction of Gas Solubility The fundamental concept of this approach is that the chemical potential of a vapor is equal to the chemical potential of its condensate in the polymer melt, when the equilibrium condition is reached. A(G) A(P) +B(P) Equal at equilibrium A: Gas B: Polymer G: Gas phase P : Polymer/Gas Solution phase

Segment of Component A Segment of Component B Empty cell (hole) Equation-of-State for the Multi-component System (Gas/Polymer Mixture) Lattice-Fluid Model (Sanchez and Lacombe EOS) Hole Model (Simha and Somcynsky EOS)

SL Model

SS Model

(High pressure gas) Buoyancy Compensation + ) Volume of Swelling Solubility F(P,T)- F(0,T)+ ρ gas × ( + Volume of holder Initial Volume of pure polymer at P,T Apparent Solubility F is Balance Reading (Vacuum) F(0,T) microbalance Polymer Sample microbalance F(P,T) Experimental Measurement of the Solubility by MSB

Volume of Swelling Swollen volume contributed buoyancy effect is an outstanding factor on solubility measurement in high pressure conditions. Theoretical method ( Equation-of-State) to predict the swollen volume.

Theoretical Estimation of Volume of Swelling SL EOS: SS EOS:

Actual Measurement of Volume of Swelling -Pendent Droplet Method Pendent drop in high temperature and pressure cell is currently utilized to do the PVT density measurement by examining the final volume after swelling. Polymer droplet High T and P cell Scale Rod gas

Experiments

Comparison of SL EOS and SS EOS Polystyrene (PS, T g =381.4K, M w =3.30×10 5, M n = 1.07×10 5 ), A&M Styrene Corporation, (Kawasaki, Japan). Carbon dioxide (Coleman grade, 99.99% purity), BOC Canada. Materials: Equipment: MSB

a b c d e f a: Microbalance b: Measuring cell c: Temperature control device d: Gas dosing system e: Control panel f: Data acquisition system Schematic of MSB Instrument MSB

Proposed Procedure to Determine the Solubility Obtain set of Apparent Solubility (AS) experimentally. Set an initial value of EOSs interaction parameter(s). Calculate the difference of the corrected solubility and theoretical solubility:  (CS i - S i ) 2 Obtain the corresponding set of the Theoretical Solubility (S) and the density of polymer/gas mixture based on SS or SL EOS. Obtain the Corrected Solubility (CS) using the SS-based or SL- based swollen volume. Decide the optimum interaction parameter(s) by minimizing  (CS i - S i ) 2

Volume Swelling effect prediction (a)SS-based and SL-based prediction at 110 o C; (b)SS-based and SL-based prediction at 150 o C; (c)SS-based and SL-based prediction at 200 o C; (b)(a)(a) (c)(c)

Solubility of CO 2 in Polystyrene at C

Solubility of CO 2 in Polystyrene at C

Solubility of CO 2 in Polystyrene at C

Temperature Effect on Interaction Parameters of EOS K 12 of SL-EOSδ e and δ v of SS-EOS δ e = δ v =

Sub-conclusion SL EOS and SS EOS predicted different swollen volumes. Below 1500 psi, corrected solubilities from SL and SS EOS are very close to each other. Above 1500 psi, there are significant difference between the SL EOS and SS EOS in terms of the solubility measurement. The interaction parameters for SL EOS and SS EOS show different temperature dependence.

Investigation of the Solubility of CO 2 in Branched –PP and Linear-PP

Rheological Behavior Difference Between the Branched-PP and Linear PP This behavior of LCB-PP is beneficial to all the processes involving extensional flow, such as thermoforming, foaming and blow molding Branched-PP Linear-PP Branched-PP

5% CO 2 content SL-EOS SS-EOS 10% CO 2 content

Solubility for linear PP/CO 2 mixture and branched PP/CO2 by SL EOS

Solubility for linear PP/CO 2 mixture and branched PP/CO2 by SS EOS

Investigation of the Solubility of CO 2 in Polycarbonate and the Effect of Crystallinity on Solubility Tough Transparent Crystallizable (regular chemical structure) Extremely low crystallization rate (chain rigidity) Material

Uptake curve for the sorption of CO 2 in PC 160 o C 200 o C240 o C

Investigation of the Crystallization of PC induced by CO 2 at 160 o C Original PC PC treated with CO 2 at 160 o C for 24 hrs (crystallinity is 21.66%) Polarizing Light Microscope DSC

Solubility of CO 2 in PC at 200 o C and 240 o C 240 o C 200 o C

System Design for Study of Solubility Pressure inside the Die

Upgrade the primary 1.5" extruder with 30:1 L/D ratio. Upgrade gear pump (Zenith, PEP-II 10 cc/rev) for controlling the melt flow rate up to 100 g/min. Secondary 1.5" extruder with a mixing screw of 24:1 L/D ratio attached after the gear pump. Die design

Contributions

Development of experimental approach to study the solubility of gas in a polymer at elevated temperature and pressure; Development of a theoretical approach to predict the swollen volume for the polymer/gas mixture; Investigation of the solubility of various gases in different polymer melts; Solubility Study Nucleation investigation The investigation on the nucleation inside the die theory.

Research Timetable Please see the attached Report

Thank You!