With the improvement of people's living standard and health awareness, disposable medical products industry develops rapidly. An estimated 129 billion masks have been used and processed every month since the COVID-19 outbreak began. The basic components of these products are non-biodegradable polypropylene (PP) and polyethylene terephthalate (PET) fiber nonwovens, which cause incalculable harm to the environment and ecosystems. Recently, it is necessary to develop biodegradable disposable sanitary products with the promulgating of plastic restriction or prohibition in various countries and regions.
Cellulose is one of the most abundant biomass on earth, renewable and biodegradable. Cellulose nonwovens have been widely used in personal care, cosmetic, medical and other fields due to their good air permeability and water retention. However, cellulose nonwoven fabric is not suitable for direct use in absorptive sanitary products, because the main function of this kind of product is to promote the rapid penetration of liquid into the absorption core layer and effectively prevent backosmosis. The function of its surface material is not only affected by its own physical structure design, but also related to hydrophilicity. In addition, breathability is another key property for such product applications, as moisture and heat generated by the body need to be continuously drained through the breathable pores to keep the skin dry and comfortable. Therefore, it is of great significance to develop cellulose nonwovens with both hydrophobic and good air permeability.
Recently, A research team from Donghua University published a paper entitled "Hydrophobic, Breathable cellulose nonwoven for Disposable Hygiene Applications "article. The research team proposed a simple and efficient one-step modification method that effectively converts a completely hydrophilic cellulose nonwoven substrate into a highly hydrophobic fabric (water contact Angle 130 -- 135°) by introducing three hydrophobic functional groups into the cellulose structure. More importantly, by adjusting the concentration of the modifier and optimizing the type and degree of substitution of the isocyanate, the air permeability of the modified fabric can be well maintained (±6%). The effects of modifier types and concentrations on fabric structure and key properties (hydrophobicity, air permeability, breaking strength, flexibility) were systematically investigated.
The results showed that three mono-isocyanates (tert-butylisocyanate TBIS, m-toluene isocyanate MTIS and 3-isocyanate propyl trimethoxysilane ISPTMOS) were successfully grafted onto cellulose by one-step ammonia esterification. By adjusting the degree of substitution of hydrophobic groups, the inherent air permeability of hydrophobic fabrics is kept at the best level (1300-1400 mm/s). The contact Angle of cnW-TBIS (5 wt%) modified fabric is 132.5°, which is 5.9% higher than that of the original fabric (1337 mm/s). The contact Angle of cnW-MTIS (1 wt%) and CNW-ISPTMOS (0.5 wt%) modified fabrics is 132.7° and 134.2°, respectively, and the air permeability is slightly lower than that of the original fabric. In addition, the breaking strength of these fabrics is greater than 80 N/5cm, and the flexibility is similar to that of the original fabric. It can basically meet the performance requirements of absorptive sanitary products.
In addition, the hydrophobicity and air permeability can be adjusted for different types of cellulose fabrics to a certain extent. This method has guiding significance for the post-finishing stage of nonwovens.