# High-Temperature Tensile and Creep Properties of Highly Strong Heat-Elongated Polypropylene

## TL;DR

This study shows that heat-elongated polypropylene retains high strength and creep resistance at high temperatures, even after long-term annealing.

## Contribution

The paper reveals the unique deformation mechanisms behind the high-temperature performance of heat-elongated polypropylene.

## Key findings

- Elongated PP showed 102 MPa yield stress at 120 °C after long annealing, much higher than unelongated PP.
- Crystalline fibrils suppressed chain motion, leading to excellent creep resistance despite thermal deterioration.
- Fragmentation of lamellae was observed in elongated PP but suppressed in long-annealed samples.

## Abstract

We investigated the high-temperature tensile and creep properties of highly strong heat-elongated polypropylene (elongated PP) before and after long annealing for 21 days at a high temperature of 120 °C. Despite the thermal deterioration caused by the long annealing, the elongated PP exhibited high tensile strength. The yield stress values of the elongated and long-annealed (LA)-elongated PP obtained from engineering stress–strain curves were 60 MPa and 102 MPa, respectively, at 120 °C, whereas that of the unelongated PP was 8 MPa. Due to the suppression of crystalline chain motion at high temperature caused by the presence of crystalline fibrils connected to lamellae, as indicated by the high elastic modulus observed using a dynamic mechanical analyzer, the elongated PP also exhibited excellent high-temperature creep properties despite thermal deterioration. Small-angle X-ray scattering and DSC measurements revealed that lamellae were fragmented in the elongated PP, while the fragmentation of lamellae was suppressed in the LA-elongated PP during tensile stretching and creep. These characteristic deformation behaviors might also provide excellent high-temperature properties. The excellent high-temperature properties of the elongated PP are promising for industrial applications that require resistance to high temperatures.