How is soy fabric made?
The basic raw material that is used to obtain soy fibers is the soybean. These protein fibers are present within each bean but their extraction involves certain chemical treatment and thus classifies it into the category of regenerated fibers. The production process involves protein extraction and about 40Kg of protein can be derived from 100Kg of soybean residue. In simple words, the production process begins with the stripping of fibers from the beans but these fibers are quite coarse and so are processed chemically. The protein present in the soybean is firstly broken by the action of heat, alkali or enzymes which are then filtered and extruded through spinneret by the process of wet spinning. Let us now understand the production process in more detail.
• Extraction of oil:
This step involves cleaning of beans followed by decortication and dehulling which removes the outer cover of the beans which is followed by the conditioning of cleaned beans at 70 and steeping in hexane to get rid of oil. The oil removal is achieved by pressing and extraction. Also, the oil is a valuable by-product which is extracted from the processing of hexane solution. The resultant oil-free bean is exposed to steam for removal of solvent and is called a meal.
• Extraction of protein:
This step includes spherical protein being distilled from the oil-free soybean meal and then refined. Firstly, the soybean meal is soaked in a dilute alkali (1% Sodium sulphite) for about one hour to one half-hour which dissolves the protein and the resultant solution is then filtered or sieved to separate the protein. The protein is then precipitated at a pH of 4.5 using sulphuric acid and resultant protein obtained is creamy white powdered form.
The soybean protein has a globular structure and is subject to pose hindrance during the spinning process and so it undergoes denaturation and degradation process which involves the use of alkali, heat, or enzymes using bioengineering technology. These processes are necessary to convert the protein solution into spinnable fiber spinning dope.
• Preparation of spinning solution:
The protein extracted from the above step is then dissolved in an alkaline solution of sodium hydroxide (caustic soda) which is then filtered to get rid of undissolved substances and deaerated using the vacuum. The resultant solution is then left to age to obtain the right viscosity at a certain temperature and thus uniform spinning solution is prepared.
• Wet spinning and fiber formation:
The viscous solution is made into fibers by the process of wet spinning. The viscous solution is extruded through a spinneret (sieve-like device having several holes at its base) in a water bath consisting of non-volatile solvent (2% sulphuric acid) and 15% sodium sulphate or sodium chloride for dehydration followed by solidification of fibers by coagulation.
The fibers are then hardened by immersing the filament fibers into formaldehyde. Formaldehyde also helps in the cross-linking of fibers and thus increases crease resistance and other mechanical properties.
Followed by the drawing process wherein the fibers are stretched to impart strength. The fibers are then washed and dried and cut into various lengths as per the end-use. The fibers are then treated with certain finish applications such as heat settings. And finally, fibers are spun and then woven into the fabric.