4.1.5 Applications of new polymer materials in ski...
With the development of industry and the progress of science and technology，people have put forward higher requirements for skin protective products.PPE should not only achieve the protective function，but also should be comfortable，simple and light to wear.At the same time，skin protective agents（e.g.，daily sunscreen）also need to be more safe and effective.With the development of new polymer materials and its application in the field of skin protection，these requirements can be partially realized.
1.New polymer materials used in the manufacture of protective products
（1）High performance fiber for protective clothing
①Poly（p-phenylene benzobisoxazole）（PBO）fiber：PBO fiber is a high performance fiber prepared by liquid crystal spinning of PBO polymer.This kind of fiber has the highest strength and modulus at present and is considered to be a super fiber of the century.At present，this fiber in our country is still under research and development.PBO fiber has four special properties：a.good heat resistance and flame retardancy；b.high strength，modulus，impact resistance and wear resistance；c.excellent chemical stability；d.excellent surface adhesion，color fastness to light and dyeing.PBO fiber can be used as heat-resistant and flame-retardant materials，as well as high-strength and high-tension protective clothing，such as fire clothes，furnace overalls，welding overalls，cutting-proof overalls，and safety gloves.
②Polybenzimidazole（PBI）fiber：PBI fiber is non-flammable in the air with excellent heat resistance，and can even be used for a long time at 350℃.The fiber is excellent in stability to chemicals and good tolerance to carbonic acid，hydrochloric acid and nitric acid.The density is 1.43 g/cm3，and the strength and elongation are similar to those of viscose fiber.The high moisture regain（about 15％）of PBI fiber prevents static electricity generation in the production process；thus，it is excellent in textile processing performance.Moreover，the wearing comfort of protective clothing made of PBI fiber is similar to that of natural fiber and much better than that of other synthetic fibers.Since the PBI fiber is smoke-free and non-toxic at high temperature，it can be used to make protective clothing for high-temperature furnace workers，welders and sand workers，as well as racing suits，flight suits and life suits.
③Polytetrafluoroethylene（PTFE）fiber：The density of PTFE fiber is 2.2 g/cm3.The tensile strength is not high（about 13 cN/tex），but the PTFE fiber is excellent in chemical stability，and its chemical stability is higher than that of all other natural fibers and chemical fibers.At the same time，PTFE fiber can be used not only at high temperature，but also at low temperature.Therefore，it is the best weather-resistant fiber among all kinds of chemical fibers.PTFE fiber also has good heat resistance and radiation resistance，and PTFE fiber itself does not have any toxicity.As a kind of high-tech fiber，PTFE fiber has important applications in aerospace and medical and health fields，and is often used to make spacesuits，shielding clothing and medical protective clothing.
（2）Gas mask material：With the development of synthetic rubber industry，more and more kinds of synthetic rubber with excellent comprehensive properties are being used as cover materials，such as butyl rubber，chlorinated butyl rubber，brominated butyl rubber，silicone rubber，EPDM rubber and polyurethane.Brominated butyl rubber is better than other butyl rubber in curing speed，aging resistance，adhesion，weather resistance and fatigue resistance；thus，it is more suitable for cover material.Silicone rubber is tasteless and non-toxic，and has no adverse effect on human body.Meanwhile，silicone rubber has excellent physiological inertia，and it reacts slightly with human tissue.Therefore，the cover materials using silicone rubber are more popular in the wearing comfort，adaptability and facial leakproofness.
（3）Mask material：The medical mask is composed of a mask face and a tension band，in which the mask face is divided into three layers：inner，middle and outer.The inner layer is made of skin-friendly material（e.g.，ordinary sanitary gauze or non-woven）；the middle layer is isolation filter layer（e.g.，ultra-fine polypropylene fiber melt-blown material layer），and the outer layer is a special material bacteriostatic layer（e.g.，non-woven or ultra-thin polypropylene melt-blown material layer）.The protective indexes of the mask mainly include the filtration efficiency of the foreign body，the anti-splashing performance of preventing the invasion of external liquid，and the tightness of preventing the inhalation of the foreign body caused by the different shape of the mask.The main raw materials of medical non-woven masks are anti-adhesive cloth and melt-blown cloth made of thermoplastic polymer；yet，with the sharp increase in the use of disposable masks，such masks will increase the environmental pressure of post-treatment.In addition，this kind of mask also needs to be improved in terms of comfort and hygroscopicity.For example，after wearing a medical non-woven mask for a long time，the plastic strip of the mask is easy to damage the skin around the nasal bridge and cheek.At the same time，due to poor hygroscopicity，the filtration performance of this kind of mask will decrease after getting wet.
（4）Sunscreen agents：The application of nanotechnology in the field of sunscreen cosmetics can be divided into two kinds：one is to make cosmetics into nano-sized powders，and the other is to use nanocarriers to carry ultraviolet absorbents.Commonly-used nanocarriers mainly include liposomes，solid lipid nanoparticles（NPs），nano-emulsions，microspheres and others.
Among the physical ultraviolet shielding agents，iron oxide，titanium dioxide，zinc oxide，kaolin and talc powder are commonly-used substances.Usually，the size of NPs is less than tens of nanometers，and titanium dioxide（TiO2），zinc oxide（ZnO），alumina or iron oxide of this specification have a good shielding effect on ultraviolet.Zinc oxide and titanium dioxide NPs are broad-spectrum inorganic ultraviolet shielding agents，which have been widely used in sunscreen cosmetics in recent years because of their good shielding performance，safety，stability，heat resistance and certain antibacterial properties.According to the properties of different sunscreen agents，different sunscreen agents can be compounded to enhance the effect of sunscreen.The composite of UVA sunscreen and UVB sunscreen，organic absorbent and inorganic scattering agent can improve the performance of sunscreen products，which is also an important research direction to improve sunscreen products.For example，the absorption performance of titanium dioxide NPs is better at the wavelength of 280-350 nm and weaker at other wavelengths.Zinc oxide NPs is a broadspectrum sunscreen，while its absorption property at short wavelength is worse than that of titanium dioxide NPs.However，it can provide broad-spectrum UV protection.Some researchers have prepared a broad-spectrum sunscreen with ZnO/TiO2 composite NPs，which combines the advantages of TiO2 NPs and ZnO NPs.This composite particle has a strong ability to shield against ultraviolet and has a broad-spectrum sunscreen effect.In addition，organic sunscreen and inorganic sunscreen can be compounded to improve the safety of products and reduce the cost of sunscreen development.(https://www.daowen.com)
Different delivery systems directly affect the performance of sunscreen.At present，the nano-systems used in sunscreen include mesoporous silica NPs，lipid NPs，nano-emulsions，while non-nano-systems include particles or microspheres，liposomes and cyclodextrins.The application of these delivery systems in cosmetics can improve the stability of active components，promote penetration and reduce irritation by the following ways：①There is no direct contact between active substances and skin components，and these systems can reduce potential toxicological risks.②These systems can reduce the photodegradation of active substances.③These systems can promote the effect of UV-active substances and improves the effect of sunscreen.④Since some nanocarriers themselves can scatter or reflect UV，it can reduce the use of UV absorbers and achieve a synergistic UV blocking effect.⑤The adverse interactions that may occur between various components in sunscreen formulations can be eliminated.Although the materials and structures of carrier systems vary widely，biodegradable materials（e.g.，lipids or biodegradable polymers）should be preferred since they play key roles in improving chemical and physical stability.
2.New polymer materials for solving problems accompanying the use of protective products
（1）Polymer dressings for preventing skin damage caused by PPE：The key to preventing device-related pressure injuries is to reduce local skin pressure and shorten the compression time.Under the premise to ensure the protective effect，soft plastic PPE has strong compliance with the skin，relatively uniform pressure distribution，and relatively little local pressure.In areas where pressure is concentrated and there is repeated rubbing（e.g.，the upper edge of goggles，the upper edge of the bridge of the nose，and the ear-closing parts of facemasks），the application of a dressing can help prevent pressure injuries by redistributing and reducing the pressure and avoiding the friction caused by relative displacement.Many types of hydrogel dressings，hydrocolloid dressings，and foam dressings are used in clinical practice to prevent pressure injuries.
Hydrogel has a rich water content and three-dimensional network structure，and has many characteristics that are beneficial for wound healing.Hydrogel dressings have good biocompatibility and compliance，as the porous structure guarantees breathability and absorbs and releases moisture to ensure that the skin moisture content is appropriate.Hydrogel also has cooling and analgesic effects（Figure 4-3）.
Hydrocolloid dressings are fabricated from colloidal，gel-forming materials carboxymethyl cellulose，mixed with elastomers and adhesives.Hydrocolloid dressings consist of two main layers.The outer layer generally consists of polyurethane，and it protects the wound from bacteria，foreign debris，and shear forces.The inner layer is a selfadhesive layer mainly composed of a hydrophilic polymer matrix.After water absorption，a modification in the physical state occurs because of the gel formation，which could help to reduce the pressure or shear force directly on the skin tissue.Previous studies reported that the application of hydrocolloid dressings could significantly reduce the device-related pressure injuries of tracheotomy.Using hydrocolloid dressings can reduce the pressure by PPE（e.g.，goggles）.
Foam dressing is a decompression dressing with the thickness of 0.5 cm.Since the dressing is covered with a foam pad，it can effectively buffer and disperse the local pressure.The dressing is soft，smooth，waterproof and breathable.A protective film can be formed locally to reduce the pressure and friction on the skin after the dressing being firmly pasted.In addition，the dressing can also absorb a large amount of exudate，thereby effectively preventing impregnation，and comprehensively reducing the erosion and irritation caused by moisture on the skin.However，its compliance is not as good as hydrogel dressing and hydrocolloid dressing because of the thickness and material characteristics.Care should be taken during use to not affect the tightness of goggles and masks.
In summary，wound dressings have important therapeutic effects on treating skin damage caused by protective products，especially pressure injuries.These dressings could accelerate wound healing while protecting wounds.
（2）Anti-fogging coating reduces fogging of goggles：The material of the goggles is mainly polycarbonate（PC），which has strong impact resistance，high refractive index and thin lenses.The anti-fogging methods for this transparent plastic material mainly include：①variation of the temperature difference between the substrate and the air through heating methods（e.g.，electricity and radiation）；②using an anti-fogging agent to change the wettability of the substrate surface.By making the surface hydrophilic，a water film is formed to spread on the substrate，and finally the light transmittance of the substrate is increased.The first method is complicated in process and the conditions used are harsh while the second method is more practical in daily life.According to the main components of antifogging agent，it can be divided into surfactant-type anti-fogging agent，polymer type antifogging agent，organic-inorganic hybrid anti-fogging agent，photocatalytic super-hydrophilic anti-fogging agent and new nano-structure hydrophilic anti-fogging agent，etc.Scientists also have conducted a lot of research on organic-inorganic hybrid type，nano-photocatalytic type and other new anti-fogging agents，and have made certain progress.With the increasing application of protective products，anti-fogging agents used in plastic materials need to have more excellent performance to meet the demand.