The influence of long chain branches of LLDPE on processability and physical properties

Paula Cristina Dartora,Ruth Marlene Campomanes Santana,Ana Cristina Fontes Moreira

doi:10.1590/0104-1428.1732

Paula Cristina Dartora, Ruth Marlene Campomanes Santana + Show 1 more

Open Access

https://doi.org/10.1590/0104-1428.1732

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Abstract

Two polyethylene-based on single-site metallocene catalyst (mLLDPE) were selected to characterize the effect of long chain branching (LCB) on blown film processability, optical and mechanical properties. 13C NMR and parallel plate rheology were used to identify LCB presence on LLDPEs. Blown films were produced from 100% LLDPEs using three different machine direction (MD) stretch ratios. When the same processing conditions for the two LLDPEs grades were used, better processability was observed for LLDPE with LCB. In relation to mechanical and physical properties, Elmendorf tear and optical properties were highly influenced by the presence of LCB. Tear resistance is affected by film orientation and is inversely proportional to the level of LCB in the polymer. It was observed a reduction of 50% in the MD tear strength when comparing with the polymer without LCB. However, haze decreases significantly with the presence of LCB, about 40%.

Highlights

Polyethylene is the most useful polyolefin in the world
It can be assumed that they are similar in their molecular structures in relation to short chain branching (SCB) amount and molecular weights[23]
The characterization of long chain branching (LCB) in linear low density polyethylene (LLDPE) was obtained by 13C nuclear magnetic resonance (NMR) and rheology analyses

Summary

Introduction

Polyethylene is the most useful polyolefin in the world It is available commercially as groups of polyethylene: high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra high molecular weight polyethylene (UHMWPE) and very low density polyethylene (VLDPE)[1]. The package shows the product to the costumer, so it is important that the film have low haze[2,3]. They are basically produced by blown and cast film processes. Structural parameters, such as density/crystallinity, molecular weight and its distribution, short chain branching (SCB) / long chain branching (LCB) length and amount and crystalline morphology are the key factors that control the properties

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