Nonwoven manufacturing processes
The three key manufacturing processes for producing nonwovens are dry – laid process, wet laid process and spun – bonded process. (50)
1- Dry laid process- dry process nonwovens are often called carded nonwovens because textile cards are used as a web- forming apparatus, so two types of webs are formed , oriented and cross-directional web, and web can be bonded using thermal , mechanical or chemical bonding. Dry laid fabrics are based on a textile staple fibres usually 3-4 cm long. Special requirements however can be met by different deniers, length or fibre type. (51)
This process was used in this research using carding machines to produce an oriented web laid down at or near alternating 90 o angles on another oriented web of a moving belt called cross lappers to produce a cross- directional fibrous web, as cross- laying is very successful with heavy weight webs which was needed in this research.
2- Wet- laid process , The wet-laid process is similar to the paper making techniques . The process comprises the following operations : (a) preparation of a water suspension of the fibres, (b) wet-laying on a condensing unit, (c) de-watering , and (d) drying. The process of chemical impregnation is also included depending upon the raw material used and properties of end- products. (50)
3- Spun – bonded process – This process integrates fibre production with web forming and nonwoven fabric finishing . Spun bonding is a continuous process where fibres, mostly polypropylene, polyethylene or polyester, are melt – spun from spinneret and plates. The resultant flat curtain of fibres is stretched and laid down randomly on a moving web take – up belt to be bonded . (48) The produced fabrics generally have a random fibrous texture but they can also have an orderly arrangement of fibres in order to achieve optimum strength, this is accomplished by air- drawing , through there are processes which use on-line mechanical drawing of the filaments. (52)
Like the dry-laid process , thermal , chemical , and mechanical bonding can be employed. (50)