With country's strong support for environmental protection and deepening of people's environmental protection concept, low-smoke, halogen-free flame retardant materials will become development trend of flame retardant materials in future. TPU has excellent comprehensive performance, but as a cable material, its cost and hardness are relatively high, which limits its further promotion in market. How to reduce cost of materials while maintaining excellent performance of TPU materials. You might as well try mixing and modifying lower cost, better processability EVA with TPU.
1. TPU and EVA materials
TPU is an elastomeric polymer containing carbamate functional groups (-NH-COO-) in molecular chain, usually by addition reaction of an oligomeric polyol (polyester or polyester) with a polyisocyanate, and then obtained by reaction with a chain extender. general structural formula is -(AB)n-. Among them, A is a hard segment that is formed as a result of reaction of various isocyanates and low molecular weight chain extenders (BDOs); B - soft segment of polyester or polyester polyol with a molecular weight of 500-3000.
Fig. 1. TPU
EVA is English abbreviation for Ethylene Vinyl Acetate. EVA is a copolymer of ethylene (E) with vinyl acetate (VA), as shown in Figure 2. EVA is easy to process and mold, and can be processed by extrusion, injection molding, blow molding, thermoforming, and other processing methods. The thermal degradation of pure EVA occurred in two stages: vinyl acetate chain began to break at 205°C, branched vinyl acetate chain, at 289.1°C, and main polyethylene chain cracked at 411.6°C.
Drawing 2. Eve
With low melting point, good fluidity, polarity and no halogen, it can be compatible with a variety of polymers and mineral powders, with balanced mechanical and physical properties, electrical properties and processing properties, and price is low High, sufficient market supply. According to the content of VA (vinyl acetate), it can be divided into three types, as shown in Table 1-1.
Table 1-1 Classification of EVA materials
2. Benefits of combining TPU and EVA
Mixing and modifying TPU and EVA can not only maintain excellent wear resistance and mechanical properties of TPU; The viscosity of EVA melt will decrease rapidly as extrusion processing temperature and shear rate increase, and users only need to adjust temperature. extruder and screw speed, while price of EVA is slightly lower, can reduce cost of wire and cable materials. Both TPU and EVA contain ester groups, so compatibility is relatively good. If you want a product with better compatibility, you can add maleic anhydride grafted EVA (EVA-g-MAH) and two materials can be mixed. with excellent characteristics is obtained by modification.
3. Halogen free flame retardant for blending TPU and EVA
TPU and EVA have excellent performance and wide application prospects, but due to poor fire resistance, they are accompanied by black smoke and a clear dripping phenomenon when burning.
Halogen-containing flame retardants have advantages of good polymer compatibility and high flame retardant performance, but their use is limited due to emission of harmful gases during combustion. Inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide will not release toxic gases during combustion, but a large amount of additive is required to achieve flame retardant effect, and due to incompatibility between flame retardant powder and polymer resin, overall performance of composite.
Compared with above flame retardants, typical intumescent flame retardants (IFR) are composed of three parts: an acid source, a carbon source, and a gas source. More and more used in wire and cable materials.
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