Inherent Flame Retardant Fibres for Protective Textiles

Abstract

This study examines the thermal shrinkage behaviour of various fibres by exposing them to 180°C for 30 minutes. During testing, both moisture (weight) loss and changes in physical appearance were monitored. The results revealed that fibres such as PBO, Meta Aramid, Para Aramid, Novoloid, ABPBI, and Polyacrylate exhibited strong heat resistance, showing minimal weight loss and maintaining their structural integrity—traits that make them ideal for high-temperature applications. Conversely, fibres like FR Nylon and FR Viscose displayed moderate stability; they experienced some shrinkage and discoloration but retained their overall structure. In stark contrast, UHMWPE showed poor thermal resistance, as evidenced by melting, indicating that it is unsuitable for environments with high heat. Overall, these findings highlight the critical importance of selecting appropriate fibres based on their thermal performance for specific engineering applications that require heat resistance. This study is also very important for spinning companies looking to develop blended, inherently flame-retardant fibres for protective textiles.

Introduction

The integration of inherently flame-retardant (FR) fibres is critical for the development of protective textiles, particularly in applications where both high performance and wearer comfort are essential. Protective clothing—such as firefighter suits, proximity suits, gloves, and other safety equipment—typically incorporates multilayered fabric structures to guard against extreme thermal and mechanical risks. To design these materials effectively, it is imperative to understand the thermal behaviour of inherent FR fibres under high-temperature conditions, even during short exposures, as this knowledge directly informs material selection and design strategies.

Inherent FR fibres—including aramid, flame-retardant viscose (FR viscose), modacrylic, and others—are celebrated for their resistance to ignition and their ability to slow flame propagation, properties that stem from their specific chemical compositions(1,2). For instance, aramid fibres exhibit excellent heat resistance due to their aromatic polyamide structure, which remains stable at temperatures often exceeding 400°C with minimal degradation. Similarly, modacrylic fibres derive their flame-retardant qualities from a halogen-containing structure that releases flame-quenching gases during decomposition. Although FR viscose, which is derived from treated cellulose, provides inherent flame-retardant properties along with superior moisture absorption and comfort, its heat resistance is generally lower than that of aramids.

The overall performance of these fibres is influenced not only by their individual properties but also by their interactions within blended and multilayered textile systems. Research indicates that the heat resistance of FR fiber blends can vary significantly depending on the blend ratios and compatibility of the components. For example, studies have demonstrated that blends like aramid-modacrylic, modacrylic/cotton, polyacrylate/wool, aramid/FR viscose can exhibit synergistic effects, thereby enhancing the overall heat resistance (3,4). However, improper blending or poor compatibility among fibres can result in uneven degradation, shrinkage, or loss of mechanical integrity during thermal exposure, ultimately compromising the protective performance of the final product (5-7). 

Evaluating the thermal behaviour of FR fibres at the pre-yarn stage is therefore essential for yarn manufacturers. By analysing factors such as degradation patterns, shrinkage, and weight loss under high-temperature conditions, manufacturers can gain valuable insights into the fibres’ heat resistance. This understanding allows for the optimization of blending processes, ensuring uniformity and compatibility in the final yarns, and helps predict the performance of the resulting fabrics. Studies have shown that thorough pre-yarn evaluations can significantly reduce production defects—such as uneven shrinkage or pilling—that are common in improperly blended yarns (8-11). 

This article explores the thermal shrinkage and degradation of fibres when exposed to high temperatures. By examining the patterns of thermal shrinkage and associated changes in physical appearance, the study provides crucial insights for optimizing fiber blends in protective textile applications. The findings underscore the importance of pre-production evaluations, which are very important for spinning units before opening the complete bale for blending and yarn production. 

Materials and Methods

Fibres such as para-aramid, meta-aramid, FR-viscose, modacrylic, and others were sourced from trusted suppliers, and properties such as fibre length and fineness of fibres are given in Table 1. To evaluate their properties before using them in yarn production, the fibres were exposed to a temperature of 180°C for 30 minutes. Each fibre sample was initially weighed and was measured again after exposure to determine the moisture content. Also, any changes in physical appearance after exposure were assessed for each fibre.

Table 1. Fibres Properties

Fibres	Fineness (denier)	Length (mm)	Tenacity(cN/tex)	Elongation(%)	Moisture regain (%)
FR Viscose	1.5	51	18-20	15	8
Meta Aramid	1.5	50	22-28	28	2
UHMwPE	1.5	38	≥250	4.0	0
Para Aramid	1.5	51	80-100	3.6	2
PBO	2.0	51	≥350	3.5	1.5
FR Nylon	1.5	51	15	17	3.5
Modacrylic Green	2.0	51	≥12	23	2
PBI	1.5	51	15	30	13
FR Polyester	1.5	51	25	15	0.8
Novoloid-Para aramid 50:50	1.5	51	NA	NA	NA
PBI Para-aramid 90:10	1.5	51	NA	NA	NA
Polyacrylate	2.0	60	13	40	12
Chorofibre (PVC)	2.0	20	20	25	0.5

Results and discussion

Exposing the fibres to 180°C for 30 minutes revealed diverse thermal behaviour, as summarized in Table 2. PBO, for instance, exhibited excellent heat resistance, with minimal shrinkage and only slight discoloration, underscoring its suitability for high-temperature applications. Similarly, fibres like meta-aramid, para-aramid, modacrylic, and the novoloid–para aramid blend maintained their integrity without significant discoloration, further demonstrating strong heat resistance. Green modacrylic, however, showed some shrinkage, indicating only moderate stability. The novoloid–para aramid blend also displayed minor discoloration, reflecting its good thermal performance.

Both FR nylon and FR viscose exhibited moderate stability, though clear signs of degradation were evident. Significant shrinkage was observed in chlorofibre and FR polyester, with the latter being particularly problematic due to its melting and dripping behaviour, rendering it unsuitable for protective textiles. In stark contrast, UHMwPE performed poorly under high-temperature conditions, melting completely and exhibiting the lowest heat resistance among the samples tested. It is worth noting that recent developments involve using UHMwPE fibres and filaments as a core material, with aramid and other inherently flame-retardant fibres forming the sheath.

Table 2. Test Results

S. No.	Fibres	Weight loss %	Change in Physical Appearance
			Before test	After test
1	FR Viscose	7.00
2	Meta Aramid	3.00
3	UHMwPE	0.00
4	Para Aramid	4.25
5	PBO	1.75
6	FR Nylon	1.40
7	Modacrlic Green	3.80
8	ABPBI Dark Brown	12.50
9	FR Polyester	0.00
10	Novoloid-Para aramid 50:50	3.10
11	Chorofibre	0
12	PBI Para-aramid90:10	10.00
13	Polyacrylate	13.24

Other fibres, including PBI/para-aramid, ABPBI, and polyacrylate, showed no visible degradation, making them excellent candidates for blending and spinning into inherently flame-retardant yarns. Each fiber type presents unique characteristics under heat exposure; for example, aramids such as meta-aramid and para-aramid are highly heat-resistant, maintaining their structural integrity even above 180°C. In contrast, while FR viscose offers superior comfort and moisture management, it exhibits lower heat resistance and begins to degrade at elevated temperatures. Meanwhile, modacrylic and polyacrylate fibres strike a balance between thermal resistance and elasticity, which makes them popular choices for blended protective textiles.

Summary

Fibres such as ABPBI, PBO, novoloid, meta-aramid, para-aramid, and PBI/para-aramid demonstrated exceptional heat resistance, making them ideal candidates for yarn spinning in protective textile applications. In contrast, fibres like modacrylic, polyacrylate, FR nylon, and FR viscose exhibited moderate heat resistance with slight shrinkage, rendering them suitable for blending based on specific requirements. Although UHMwPE showed significant degradation and poor performance at high temperatures, it can still be utilized as a core material when paired with aramid and other inherently flame-retardant fibres in the sheath. As the demand for high-performance protective textiles increases, the role of inherent flame-retardant fibres in delivering superior protection and comfort becomes ever more critical. By focusing on fiber heat resistance in the early stages of product development, yarn manufacturers can create innovative solutions tailored to the diverse needs of industries ranging from firefighting to industrial safety.

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