Unveiling the secret for you: Why are TPU films widely used in inflatable boats, water kites, and windproof jackets?

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This post was last edited by ljtjbx on 2016-5-12 at 16:24. In 2014, the global total production and consumption of polyurethanes reached 21.5 million tons, of which about 2 million tons were elastomers, accounting for 9.3% of the total. In 2014, China’s total consumption of polyurethanes was 9.6 million tons, of which 820,000 tons were used for elastomers, accounting for 8.6% of the total consumption, while TPU consumption amounted to 280,000 tons. The main goal of China’s 13th Five-Year Plan for TPU is to develop high-end TPU products for use in the medical, automotive, and film industries. Why are high-end TPU products for films gradually gaining favor? Shall we start by getting to know TPU first? 1. Structure and properties of TPU: TPU is a polymer whose molecular chains contain carbamate groups (-NHCOO-). It is a block copolymer with hard segments and soft segments, possessing both the plasticity and mechanical strength of plastics as well as the elasticity of rubber. Thanks to this unique structure, TPU can be widely used in: shoe materials, waterproof and breathable films, cast films, extruded pipes, hydrolysis-resistant cast films, automobiles, flame-retardant cables, and more. Second, the unique advantages of TPU materials: Compared to other materials, TPU boasts adjustable mechanical properties, with a Shore hardness ranging from 30A to 80D. It also exhibits excellent properties such as high wear resistance, tear strength, tensile strength, elongation at break, resistance to bending, oil resistance, aging resistance, weather resistance, high water resistance, high breathability, and hydrolysis resistance ； It also features environmental friendliness, good biocompatibility, non-toxicity, and no carcinogenic properties. Therefore, for now, TPU is the best choice to replace PVC. This is mainly because not only is its tensile strength **better than that of PVC, but its resistance to low temperatures is also incomparable to PVC’s ； Furthermore, its properties such as biodegradability, antibacterial activity, and absence of plasticizers are all superior to those of PVC. For high-end products, TPU is a good alternative to PVC. Currently, TPU materials are widely used in fields such as footwear, clothing, medical products, industrial goods, and baby products, especially in the medical sector. Table: Application Categories of TPU
Uses: Materials for the outer layers and linings of shoes such as sports shoes, hiking boots, snowshoes, golf shoes, field shoes, and skating shoes. Materials for the outer layers and linings of clothing items such as snow jackets, raincoats, overcoats, thermal jackets, field uniforms, diapers, sanitary pads, linings, T-shirts, and sportswear. Materials for surgical gowns (hats, shoes), medical padding, ice packs, bandages, plasma bags, etc., in the medical sector. Materials for weapon sealing films, field tents, and ice packs used in military applications. Life jacket. Materials for inflatable boats and similar products, as well as their linings. Materials for sports items such as air parachutes, inflatable water bags, wetsuits, swimsuits, air cushions, sweatshirts, and slimming garments. Industrial products: fireproof materials, insulation panels, soundproof panels, waterproof seals, insulating boards, oil bags, pipes, and materials for sewer cleaning equipment. Materials for baby products and toys. Characteristics and manufacturing features of high-end TPU films: TPU films possess advantages such as resistance to low temperatures, high toughness, high strength, environmental friendliness and biodegradability, as well as “breathability.” They are replacing materials like PVC, EVA, and synthetic leather in various fields, and their consumption in China is also on the rise. As environmental awareness across society continues to grow, along with further advancements in technology, the applications of TPU are expanding continuously. From 2010 to 2014, the overall market growth rate averaged 15% per year. 1. Characteristics of TPU films: TPU films are produced by melting and extruding TPU raw material particles. These films possess advantages such as low-temperature resistance, high toughness, high strength, environmental friendliness and biodegradability, as well as \"breathability.\" They are gradually replacing materials such as PVC, EVA, and synthetic leather, especially in the film industry. For example, shoes account for the largest consumption volume due to the relatively thick thickness of the TPU films used (0.5–2 millimeters), as well as the widespread use of various types of sports shoes and outdoor hiking shoes ； Sports equipment mainly includes water jetskis, inflatable boats, and water kites, and polyether-based TPU films are primarily used in their manufacture ； Waterproof and breathable TPU film used for home textiles, windbreakers, outdoor products, and medical supplies (surgical gowns). Figure: Application of TPU in outdoor clothing. 2. Processing techniques and characteristics of TPU films. TPU films can be produced through methods such as blow molding and cast molding. Blow molding method: The raw material is melted and plasticized by a heat extruder, enters the die head from there, is expanded by compressed air and pulled, and then curled and cut into strips ； Casting method: The raw material is melted and plasticized by a heat extruder, then extruded through a slit die at the nozzle and poured onto cooling rollers to cause rapid cooling of the material, followed by stretching, slitting, and winding. Table: TPU extrusion processes: Comparison of blow molding and casting. Blow molding vs. Casting: Thickness range – 10~100μm; 50~2000μm. Mechanical properties – Small difference in strength between longitudinal and transverse directions; Large difference in strength between longitudinal and transverse directions. Control of insoluble matter – Low content of insoluble matter; Higher content of insoluble matter. Production volume – Low; High. Surface characteristics – Both sides can be smooth or frosted; Single-sided smoothness/frosting is also achievable. Crystallinity’s impact on the film – Appropriate crystallization results in a good appearance of the film along with excellent mechanical properties. Figure: The crystallinity of the TPU film is moderate. If the crystallinity is too high, it can cause melt fracture, leading to agglomeration during extrusion. As shown in the figure, there are many areas of agglomeration in the film, its appearance is rough, and its mechanical properties are poor. Figure: Excessive crystallinity of TPU films 3. Effect of the extrusion rate on TPU films: When the extrusion rate of TPU films increases to a critical value, the samples exhibit extrusion distortion. The main manifestations of distortion can be divided into: surface distortion and overall distortion. Therefore, selecting an appropriate extrusion rate while ensuring good appearance properties of the film can be helpful in improving production. 4. Characteristics of TPU films with high moisture permeability: Microporous films are generally made from polytetrafluoroethylene; through expansion and stretching, they become films with a microporous structure. These films have pore sizes ranging from 0.2 to 10 um, allowing only water vapor to pass through. As a result, the water vapor emitted by the human body can effectively diffuse outward through these pores, while water droplets cannot penetrate, thereby achieving a waterproof and transparent effect ； Hydrophilic non-porous membrane: Made primarily of polyurethane (TPU), it incorporates hydrophilic groups, resulting in a uniform and dense structure both on the surface and within its body. The surface contains certain hydrophilic groups that \"capture\" water vapor molecules released by the human body through hydrogen bonds; this vapor is then \"transferred\" out via the molecular chains as well as the pressure difference between the inside and outside of the membrane, thereby achieving excellent waterproofing and breathability properties. Comparison between molecular permeable membranes and porous permeable membranes: Compared to traditional porous membranes, TPU molecular permeable membranes have advantages such as resistance to surfactants, a higher water permeability, selective permeability, greater tear resistance, complete isolation from bacteria and odors, and lower costs. Comparison between molecular permeable membranes and porous permeable membranes: Molecular permeable membranes vs. porous permeable membranes – Resistance to surfactants: Surfactants cannot penetrate these membranes; Higher water permeability: These membranes allow higher water permeation; Selective permeability: They enable selective water passage; Non-selective permeability: Water passes through them without selection; Water expansion: The degree of water expansion is variable; Lower water expansion: Water expansion is minimal; Greater tear resistance: These membranes offer better tear resistance; Lower tear resistance: Their tear resistance is weaker; Complete isolation from bacteria and odors: These membranes completely prevent the penetration of bacteria and odors; Poor odor isolation: They provide limited protection against odors; Lower costs: These membranes are less expensive; Higher costs: They are more costly. Wind and water resistance: Both types offer wind and water resistance. High permeability: TPU membranes exhibit high permeability. TPU waterproof and permeable membranes are currently used in applications such as racing suits, motorcycle gear, golf clothing, waterproof jackets, hiking shoes, shower curtains, tablecloths, raincoats, baby bibs, nautical uniforms, fishing pants, snow coats, overcoats, thermal jackets, skiing outfits, skiing gloves, hiking gear, hunting clothes, surfing suits, horse gear, tactical vests, combat uniforms, lighting accessories, and mobile phone waterproofing components.