Polypropylene is the most commonly used raw material and the most important raw material for polymer fibers. Nearly 94% of spunbond and meltblown fabrics in my country are made of polypropylene. According to US statistics, polypropylene fibers are increasingly used in nonwoven fabrics and have largely replaced polyester and viscose fibers. In the fields of medical care, hygiene, and health care, the application of polypropylene nonwoven fabrics accounts for 50% of the total nonwoven fabrics.
Polypropylene fibers differ from other synthetic fibers in two major ways: first, their hygroscopicity is very low, which gives polypropylene fibers excellent stain resistance and almost the same dry and wet properties; second, they have the smallest density of all fibers, which gives them better coverage under the same weight conditions.
The basic properties of polypropylene fiber are as follows: extremely low density (0.91g/cm3); low moisture content (less than 0.1%); good chemical resistance (acid, alkali, solvent resistance); mildew resistance, anti-corrosion, anti-moth, antibacterial; good heat insulation, thermal insulation, insulation performance; high stiffness, good tensile strength (4.5~7.5cN/dtex); good fatigue resistance and wear resistance; good hydrolysis stability; good dyeability of stock solution (wide dyeing spectrum); temperature resistance of 120℃, melting point of 165℃; easy to regenerate.
The hydrocarbon structure of polypropylene fiber (i.e. lack of any polarity) makes it highly water-repellent, thus preventing contamination caused by polar materials. For nonwoven fabrics, this property can also be changed by appropriate post-finishing to make PP nonwoven fabrics hydrophilic or other special properties.
The melting point of polypropylene is very low (165℃), so the fiber web is suitable for hot rolling bonding consolidation processing, and the product has been widely used as a covering material for sanitary napkins and diapers.
Due to the non-ionic chemical properties of polypropylene fibers, it is difficult to dye using ordinary processes. Therefore, PP nonwovens are all made using a melt dyeing process, that is, masterbatches are mixed into the polymer chip raw materials for melt blending and spinning dyeing. In addition to product dyeing, functional masterbatches can also be added to the melt to give the product specific functions. Generally, the degradation phenomenon induced by light (ultraviolet UV) will cause PP nonwovens to fade, become brittle, and have reduced mechanical strength. Now, the method of adding anti-aging agents can be used to reduce the impact of ultraviolet rays on the product and extend the effective use time of the product.
However, it should be pointed out that PP nonwovens will decompose under gamma ray irradiation (this is a disinfection method used in the production of sanitary materials), release an odor, change color, and become brittle. This is a problem that PP nonwovens should pay attention to when used in the medical and health field.