# Compressive Properties of Polyurethane Fiber Mattress Filling Material
## 1 Introduction  
Mattresses are essential and inevitable for people's sleep quality. Higher requirements for mattresses are put forth with the improvement of living standards. Natural latex is expensive and scarce, and artificial latex is a nonrenewable resource. Spring manufacturing is a high energy-consumption industry, which is against the concept of sustainable development and cannot continuously supply a huge mattress market. Thus, there is a trend toward exploring alternatives to nonrenewable resources and environmentally friendly fibers with good performance for mattress production. Palm silk, brown mountain silk, bamboo silk and hemp fiber have been applied as mattress filling materials, but some of their properties are worse than conventional mattress material [1; 2; 3]. Environmentally friendly fiber has aroused extensive attention for its recyclability, biodegradability and eco-friendliness. Therefore, promoting the performance of environmentally friendly fiber and exploring the scope of its application as mattress filling material and upholstered furniture are possible methods to solve economic and environmental problems. Researchers have conducted abundant research on different methods of producing and modifying environmentally friendly fiber that can be applied as mattress products [4; 5; 6; 7; 8]. [PERSON] [9] found that cattail possesses not only high tensile strength and specific modulus but also the characteristics of light and stable structure and good performance on oil absorption, storage, insect resistance and lipophilic hydrophobicity. [PERSON] et al. [10; 11; 12] applied loofah to a mattress-supporting layer and studied its effects. [PERSON] et al. [12] showed that natural loofah fiber possesses a porous structure, a high elastic modulus and good corrosion resistance and hardness. Polybutylene terephthalate (PBT) fibers have not only low strength, high elongation at break and low initial modulus but also good elasticity and dyeability and a soft hand filling. It is suitable for the production of textiles with high requirements for elasticity. It is also widely used in the field of fiber. The unique properties of polyethylene glycol terephthalate (PET) fiber, which possesses high shrinkage properties, make it increasingly used in clothing, decoration and industrial use. Composite polyurethane fiber PBT/PET, one kind of polyurethane fiber with low cost that is environmentally friendly and has high resilience, is made of PBT chips and PET chips. [PERSON] [13] et al. added DOPO-based flame retardant to PET using a melt-blending method that proved to be helpful for enhancing flame-retardant properties. [PERSON] et al. [14] conducted tests of PET, and the results showed that it has a significant effect on flame-retardant introducing hexakis [p-(hydroxymethyl)phenoxy] cyclotriphosphazene (PN6)/poly (2-phenylpropyl) methylsiloxane (PPPMS) into PET. Modified PET/PBT (hereinafter referred to as PLON) is one kind of fiber with the characteristics of high resilience, strong support and good thermal insulation performance, which broadly expand its application scope in the textile industry. [PERSON] et al. [15] conducted research on cushions made of modified PET/PBT fiber. The results showed that these modified PET/PBT fiber cushions have not only equivalent supporting ability to latex but also higher resilience. A cushion made of modified PET/PBT fiber has great application potential as mattress filling material. This research aims to add ethylene-propylene side by Side (ES) chip, 3D hollow PET fiber and thermoplastic polyester elastomer (TPEE)/PET (hereinafter referred to as EJQ) chips into PBT/PET fiber by melt blending to modify PBT/PET fiber. The study also aims to explore the compressive properties and reasonable application of cushion made of modified PBT/PET fiber (hereinafter referred to as PLON). PLON is more suitable to apply as mattress filling material than PET/PBT for its high resilience, elasticity and tightness.