A Study On The Structure And Properties Of PE/PP Bicomponent Spunbond Nonwovens

With the unceasing development of technology and the increasingly fierce market competition, people's health and hygiene products is becoming more demanding, therefore the performance of nonwoven material made higher demands. The aim is to develop a softer and more comfortable, healthier and more sanitary, higher strength and more processable material. Under such conditions, PE/PP bicomponent Spunbond Nonwovens become a new generation of hygiene materials. The production processes as follows: first, Polypropylene (PP) and Polyethylene (PE) are heated to melt; next, the melt is extruded into the air from the composite spinning holes after it goes through the extruder; then the flow is drawn and become finer and longer in a certain speed, meanwhile it is cooled and coagulated in the air, so that the sheath-core PE/PP fiber is formed; after web-laying, finally the web will be reinforced to be nonwovens via calendar bonding with heat and pressure. This paper mainly focuses on those aspects: first, the cross-section structure of PE/PP bicomponent fiber and the microstructure of nonwoven fabrics are observed; the second is to optimize the parameters of the process of calendar bonding; the third is to study the breaking mechanism of nonwovens; last, the advantages and disadvantages of the structures and properties between PE/PP bicomponent spunbond nonwovens and PP spunbond nonwovens are compared and analyzed. PE/PP fiber is a differential fiber and its cross-section structure is designed in accordance with its use. The sheath-core fiber can improve hand softness and strength of nonwovens.In calendar bonding a pair of heat rollers-an engraved roller and a blank roller—is used to thermo-dot bond the fiber web. The heating temperature is the same with the melting point of the sheath component PE and PE melts and flows, while core component PP melting point is about 30℃higher than PE so that it maintains its original performance in this process. The fibers bond together and form nonwovens. The bonding only takes place in the rolling point of engraved roller.The temperature, linear pressure, linear velocity (or heating time) of calendar are three key factors, which have great effect on the quality of the bicomponent spunbond nonwovens. By orthogonal layout and variance analysis, we discussed the impact of those three parameters on the vertical and horizontal breaking strength, bending rigidity and permeability of the nonwoven fabrics. If only strength is concerned, the optimal parameters are as follows, temperature :130℃, linear velocity: 13 m/min, linear pressure: 70 kgf/cm. The analysis on the structure of spunbond nonwovens show that the bonding point is diamond-shaped and its size, number and distribution depend on the situation of the calendar. The bonding zone of PE/PP spunbond nonwovens is almost intact and remains to be monofil, while that of PP spunbond nonwovens is impaired, film-like, becoming potential weak area.The breaking of spunbond nonwoven fabrics can be divided into three stages and starts from the weak area at the junction between bonding spot and the surrongding. The weak area of PE/PP spunbond nonwoven fabric is relatively stronger than that of PP spunbond nonwoven fabrics, so it takes more time to break, and the bonding spot structure remains almost undestroyed and stretches along with the fibers around to the same direction of extension. On the contrary, PP spunbond nonwoven fabrics present us much poorer performances of the mechanical properties. The bonding spot of PP spunbond nonwoven fabric is damaged more seriously and more susceptible to break,By comparison, PE/PP spunbond nonwovens are thinner, stronger, more extensile, softer, smoother, more even, higher in air and moisture permeability, but poorer in uniformity, coverage and water repellency; PP spunbond nonwovens are on the very contrary.Strength and elongation as well as softness are important indicators of the qualities of hygiene nonwoven materials. With good softness, high strength and elongation, good air and moisture permeability and the ability to prevent reverse osmosis, light-weight PE/PP spunbond nonwoven fabrics are very suitable for the top-layer of baby diapers, sanitary napkin and so on, becoming an upgrading product for monocomponent PP or polyester (PET) calendar bonded nonwovens, or staple-fiber carded hot through-air nonwovens.