# Molecular Orientation and Mechanical Properties of Biomass-Derived Aliphatic Polyamide (PA11) by High-Pressure Compression Molding

## TL;DR

High-pressure compression molding improves the strength of a bio-based plastic by aligning its molecules and stabilizing its crystal structure.

## Contribution

A new method using high-pressure thermal compression to enhance the mechanical properties of bio-based PA11 by controlling its crystalline structure and molecular orientation.

## Key findings

- Tensile fracture strength of PA11 increased up to 2.4 times under 1000 kN and 140 °C conditions.
- The δ’ crystalline phase remained stable after cooling to room temperature without undergoing Brill transition.
- At 180 °C, increased crystallinity was accompanied by reduced molecular orientation and lower tensile strength.

## Abstract

What are the main findings?
This study demonstrated that high-pressure thermal compression molding significantly modifies the crystalline structure and mechanical properties of biomass-derived aliphatic polyamide PA11, specifically the grade Rilsan® BMN O TLD manufactured by Arkema—a fully bio-based resin derived from castor oil.The tensile fracture strength reached a maximum—approximately 2.4 times higher than that of the uncompressed sample—under experimental conditions of 140 °C and 1000 kN. This enhancement is proposed to be primarily attributable to the molecular orientation and crystallization of the δ’, which remained stable without undergoing Brill transition even after cooling to room temperature, while its crystallinity increased, as supported by POM observations, WAXS analysis, and DSC analysis. In contrast, at 180 °C, although the degree of crystallinity increased, molecular orientation decreased, resulting in reduced tensile strength.These findings indicate that the mechanical properties of a fully biomass-derived aliphatic polyamide, PA11, which exhibits crystal polymorphism, are governed by a complex interplay among phase transitions, molecular orientation, and crystallization, all of which are strongly influenced by temperature and pressure conditions.

This study demonstrated that high-pressure thermal compression molding significantly modifies the crystalline structure and mechanical properties of biomass-derived aliphatic polyamide PA11, specifically the grade Rilsan® BMN O TLD manufactured by Arkema—a fully bio-based resin derived from castor oil.

The tensile fracture strength reached a maximum—approximately 2.4 times higher than that of the uncompressed sample—under experimental conditions of 140 °C and 1000 kN. This enhancement is proposed to be primarily attributable to the molecular orientation and crystallization of the δ’, which remained stable without undergoing Brill transition even after cooling to room temperature, while its crystallinity increased, as supported by POM observations, WAXS analysis, and DSC analysis. In contrast, at 180 °C, although the degree of crystallinity increased, molecular orientation decreased, resulting in reduced tensile strength.

These findings indicate that the mechanical properties of a fully biomass-derived aliphatic polyamide, PA11, which exhibits crystal polymorphism, are governed by a complex interplay among phase transitions, molecular orientation, and crystallization, all of which are strongly influenced by temperature and pressure conditions.

What are the implications of the main findings?
If the mechanical properties of the biomass-derived polyamide PA11 can be enhanced through high-pressure thermal compression molding, it could be utilized in a wider range of applications. This suggests the potential to shift from petroleum-derived polymers to renewable, biomass-derived polymers, thereby contributing to environmental sustainability.These results suggest that, even for polymers whose crystalline phases or structures typically change upon cooling to room temperature, the method has the potential to suppress such phase transformations. This capability may improve durability against strength degradation and dimensional changes under service conditions, and we therefore consider it a topic for future study.Expanding the application of this method to other biomass-derived polymers with various crystal polymorphs may allow temperature and pressure conditions to be combined to control phase transitions, molecular orientation, and crystallization. This approach has the potential to contribute not only to improved mechanical strength but also to enhancements in a range of other material properties.

If the mechanical properties of the biomass-derived polyamide PA11 can be enhanced through high-pressure thermal compression molding, it could be utilized in a wider range of applications. This suggests the potential to shift from petroleum-derived polymers to renewable, biomass-derived polymers, thereby contributing to environmental sustainability.

These results suggest that, even for polymers whose crystalline phases or structures typically change upon cooling to room temperature, the method has the potential to suppress such phase transformations. This capability may improve durability against strength degradation and dimensional changes under service conditions, and we therefore consider it a topic for future study.

Expanding the application of this method to other biomass-derived polymers with various crystal polymorphs may allow temperature and pressure conditions to be combined to control phase transitions, molecular orientation, and crystallization. This approach has the potential to contribute not only to improved mechanical strength but also to enhancements in a range of other material properties.

This study investigates the effects of high-pressure compression molding on the molecular orientation and mechanical properties of biomass-derived aliphatic polyamide (PA11). Tensile fracture strength exhibited a significant increase—up to 2.4 times that of untreated samples—under conditions of 1000 kN and 140 °C. Differential Scanning Calorimetry (DSC) and Wide-Angle X-ray Scattering (WAXS) analyses revealed a temperature- and pressure-dependent shift in crystalline phases, suggesting a transition from α’ to phase. The δ’ phase, formed by high-pressure compression molding, is retained even after cooling to room temperature (i.e., Brill transition was not observed). In addition, polarized optical microscopy (POM) observations further supported the presence of changes in molecular orientation. This enhancement (under conditions of 1000 kN and 140 °C) is primarily attributed to the molecular orientation. However, it is also noteworthy that the formation of the δ’ phase is accompanied by an increase in the degree of crystallinity, and that this δ’ phase is retained even after cooling to room temperature without undergoing a Brill transition. In contrast, at 180 °C, although the degree of crystallinity increased, molecular orientation decreased, resulting in reduced tensile strength. These findings indicate that the mechanical properties of PA11 are governed by a complex interplay among phase transitions, molecular orientation, and crystallization, all of which are strongly influenced by temperature and pressure conditions. These findings demonstrate that high-pressure compression molding is an effective method for enhancing the mechanical properties of PA11 through controlled phase transition and orientation