Low molecular weight ‘liquid’ polymer extended compounds, impact on free volume and crosslink density studied by positron lifetime spectroscopy and stress-strain analysis according to Mooney-Rivlin

M Gruendken,D Koda,J Dryzek,A Blume

doi:10.1016/j.polymertesting.2021.107239

Abstract

Liquid polymers are used in elastomeric compounds to modify their processing and final characteristics. The material is considered as a polymeric plasticizer and is used to substitute or supplement conventional plasticizer like paraffinic or aromatic oils, or hydrocarbon resins. Their plasticizing effect and contribution to the crosslinking in sulfur cured SSBR mixtures is studied. Aromatic oil, aliphatic resin and different liquid polymers, varied in type, molecular weight and microstructure are discussed. Different plasticizing effects are shown with corresponding curing torques and Shore hardness values. The free volume – measured by positron annihilation lifetime spectroscopy - increases or decreases according to the liquid polymer's incorporation in the main polymer.

Highlights

In polymeric mixtures, plasticizers are mainly used to improve pro cessing and influence material characteristics by reducing the hardness and viscosity
The current study focuses only on an unfilled and basic So lution polymerized Styrene Butadiene Rubber (SSBR) formulation in the presence or absence of liquid polymers
The Treated Distillate Aromatic Extract (TDAE) and aliphatic resin aliphatic C5 resin (Al–C5) show higher maximum torques and hardness values compared to the liquid polymers

Summary

Introduction

Plasticizers are mainly used to improve pro cessing and influence material characteristics by reducing the hardness and viscosity. Positron Annihilation Lifetime Spectroscopy (PALS) was used to evaluate the free volume in elastomeric compounds. The lifetime of the ortho-positronium (o-Ps) is measured, which is an unstable pairing of an electron and its anti-particle, the positron, that is formed in low electron density sites These sites are considered as the free volume of the compound. A previous study has shown that the replacement of TDAE with different liquid polymers results in a lower Crosslink Density (CLD) [13]. This is due to the con sumption of sulfur by the co-reactive liquid polymer. It is compared to the rheometer curing charac teristics as well as Shore hardness values

Raw materials

Preparation of blends and sample plates

Rheology The curing kinetics of the compound were determined with an Alpha

Mooney-Rivlin stress strain analysis

Curing and hardness

Conclusion