Processing of a LLDPE/HDPE pressure vessel liner by rotomolding

E S Barboza Neto,M M C Forte,C A Ferreira,S C Amico,L A F Coelho

doi:10.1590/s1516-14392013005000168

Abstract

Biaxial rotational molding is a low-pressure process that uses a polymer powder to produce large and/or complex-shaped hollow thermoplastic goods using low cost molds, being very suitable for prototype production. In the present work, liner prototypes (Φ 78 × 280 mm) made of linear low density (LLDPE) and high density polyethylene (HDPE) blends were produced aiming to later use them as compressed natural gas type IV cylinders. The LLDPE/HDPE blend composition and the process parameters (temperature/time cycle, and rotation speed) were varied to evaluate their effect on blend miscibility and liner final properties, such as density and crystallization behavior. Blend composition and process parameters were found vital for the production of a homogeneous wall and for the liner to reach adequate characteristics for the intended product.

Highlights

Liners used for composite pressure vessels may be obtained by rotomolding instead of injection or blow molding processing, with the advantage of producing a variety of shapes at low cost and reaching higher impact strength
To determine the most suitable LLDPE/high density polyethylene (HDPE) blend composition for liners, the thermal behavior was analyzed focusing on crystallite size profile aiming to obtain a more homogeneous liner wall
Variation in HDPE content of the blend was responsible for changing temperature and processing time of the rotomolded liners, yielding different porosity contents for the studied blends

Summary

Introduction

Liners used for composite pressure vessels may be obtained by rotomolding instead of injection or blow molding processing, with the advantage of producing a variety of shapes at low cost and reaching higher impact strength. The rotomolding process requires a powdered or micronized polymer and some air bubbles can be entrapped in the molten polymeric material[6]. LLDPE/HDPE (linear low-density polyethylene/high density polyethylene) blends were studied aiming to produce liners for high-pressure composite vessels. The use of this polymeric blend instead of pure LLDPE, traditionally used for this application[3], aims to improve overall processing and properties[13,14,15]. The miscibility study is needed considering that blend interfaces would be detrimental for the intended application

Material

Blend preparation and specimens

Polymer liner prototype production

Characterization

Results and Discussion

Conclusions