Corn Fiber: A New Fiber on Horizon (Part-2)

Corn Fiber: A New Fiber on Horizon (Part-2)
Aditi Dhama
Satyam Fashion Institute, Noida, Delhi, India
Email: aaditidhama@gmail.com

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MANUFACTURING PROCESS OF CORN FIBER
First step is the process of separating starch from the bio-mass basically wet milling is the process adopted. The starch is processed into dextrose that is then converted to lactic acid using a fermentation process using bacteria e.g. Homolactic Lactobacteriaceae family. Monomer lactide collected through condensation and then purified through vacuum distillation. Using a solvent free process like Ultrafiltration, Nanofiltration and Ion-exchange process we obtain PLA resin from the lactide.

The lactic acid exists in two optical isomers L-isomer & D-L isomer. The polymer produced from D-L isomer by using direct condensation requires solvent under high pressure & high vacuum. Hence L isomer is used. Lactic acid firstly condensed to transform it into short chain PLA. It is then converted into lactic acid by using vacuum distillation. No solvent is required during distillation. The final stage is ring-opening polymerization.

Flow of Manufacturing:

Corn → Starch → Undefined Dextrose → Fermentation → Lactic acid → Direct polymerization → PLA → Melt spinning → PLA fibre

Corn fiber production sequence is:

Seeds, Soil, Water, Carbon dioxide, Sunlight
↓Grow-months↓
Biomass, ideally corn
↓Harvest/Wet Mill↓
Starch
↓Acid/Enzyme Hydrolysis↓
Dextrose
↓Fermentation↓
Lactic Acid
↓Polymerise↓
Crude Polylactic Acid Pre-polymer
↓Depolymerise↓
Crude Lactide monomer
↓Fractional Distillation↓
Pure lactide monomers
↓Blend/Polymerise↓
Polylactic Acids
↓Modification for end-use↓
Granules for extrusion etc.
↓Melt Spinning↓
"Crop-Based" Fibres

Producing the lactide with the right purity and stereochemistry to make decent fibres is not trivial. In a recent Cargill patent, the refining process, intended to be able to cope with crude lactic acid feedstock, was illustrated as follows:

Feed Crude Lactic Acid to Evaporator continuously

Remove water or solvent → discard or recycle water, solvent or by-products

Feed concentrated lactic acid to a pre-polymer reactor

Polymerize to form pre-polymer by removing water → discard or recycle water, solvent or by-products contaminated with lactic acid

Feed in catalyst→ Feed pre-polymer to lactide reactor→Remove high-boiling unreacted polymer

Remove crude lactide as vapour

Partially condense crude lactide →Remove lactide impurity as a vapour

Purify crude lactide in a distillation column →Remove lactide impurities

Remove purified lactide as high-boiling bottoms from the column

Polymerisation

Yarns, fabrics and garments made from corn fibres can be processed on conventional machinery through all of the manufacturing stages; there is no need for any capital investment in plant. In many of the downstream sectors fibre spinning, yarn spinning, fabric production and dyeing and finishing- corn fibre is comparable with polyester. Both are available in filament and staple form; they are melt spun ;weaving and knitting set up conditions are similar; fabrics can be heat treated to give dimensional stability and they are both dyed with disperse dyes.

YARN PROCESSING OF PURE CORN AND ITS BLENDS
Corn fibre is processed into pure Corn yarn and also blended with natural fibre like cotton, wool, silk and synthetic fibres that include polyester, viscose etc. by ring spinning method which include:

COTTON SPINNING SYSTEM 
Spinning through cotton spinning system involves following stages:

A. OPENING, CLEANING AND BLENDNG 
Staple fibres in form of large bales arrive at the yarn processing plant. It is very important to separate or open the fibre mass to single fibre state or as close as possible. the oening and blending machine separate and blend the fibres from different bales.

B. CARDING 
The carding is one of the most important processes of short staple spinning. Carding is a process where the tufts of fibres are converted into individual fibre forms. Carding is often called the heart of the spinning because of its main cotton opening mechanism. It is very important to individualize fibres in the card to make them able to convert in yarn in the later processes.

C. COMBING 
This is an optional step for high quality of superior evenness, smoothness, fineness and strength, fibres are combed. Card sliver are fed to the machine where several card slivers are combined. This smoothness out the card sliver pulls out the fibres into layer and reforms a new sliver called as a comb sliver.

D. DRAWING 
In the Drawing section is doubled, blended and drafted to parallel all fibres and to control and even sliver for production of high quality yarn.

E. ROVING 
Roving is an intermediate process during the conversion of fibres into yarn. The purpose of roving is to prepare a better input package for the ring frame. The roving is produced on compact small packages called bobbins, which are more convenient to transport and have less chances of damage as compared to sliver cans. That is why roving is still an important process in ring spun yarn.

F. SPINNING 
The final process in this system is the spinning operation. During spinning, the roving is attenuated to the desired diameter called the final draft and the desired amount of twist is inserted.

G. WEAVING 
Weaving is the process of interlacing warp and weft yarns for constructing fabric.
Weaving
WARPING
Tensions should be kept low. In general, 0.3 to 0.35 g/Denier has been adequate for warping without compromising the fiber’s stretch characteristics nor the warping efficiency. Where Friction Textured yarn is to be used in the warp then this should be clearly specified to the yarn supplier to ensure sufficient lubrication (0.75% oil content if the yarn is to be sized), and a high degree of interlacing (normally 110 tacks/meter level). When warping spun Corn fiber yarns and a break occurs, care should be taken that the ends are tied two inches above the break point of each end. Due to the high fiber resiliency the yarn tends to un-twist near the break point and create weak spot.

SIZING
Friction Textured Filament Corn fiber yarns have been warped and woven successfully without sizing. These yarns were specifically prepared with 1.75% oil content minimum, and a compaction level of 110 tacks/meter (NSY, no size yarn). However, the success of being able to use the Corn fiber Friction Textured Filament yarns depends on many variables. These include yarn Denier and filament count, fabric construction such as density and weave design, loom type and operating conditions. Size selection, as outlined before is dictated by the conditions necessary for its removal during wet processing. Both PVA and Polyester (WD size from Esatern Chemicals) are suitable for sizing the Corn fiber yarns. Both can be applied in relatively mild conditions, size solution and drying temperatures). Also both can be washed off at mild alkaline conditions (below a pH of 7.5), and relatively low temperatures (normally not exceeding 80º C). Further yarn lubrication can be achieved by a kiss roll application of an over-oil after the yarn has been sized and dried, before the Slasher Reed.

The amount of size required on the yarn is dictated by the amount necessary to have a good encapsulation of all the yarn fibers. Typically, for a Filament Corn fiber yarn 4 to 5% size pick-up, and for staple yarn 8 to 10% size pick-up have produced good results.

Typical sizing conditions for filament Corn fiber yarn are listed below:
  • Type of size; PVA mixed at 10% solids solution.
  • Size box Temperature 35 to 40º C
  • Drying temperature of 75 to 85º C
  • Neutral to slightly overfeed (6%) warp sheet tension.
WEAVING
No special points beyond those normally used for the fabric construction/yarn counts/loom types have been noted in weaving trials to date when correct warp yarns and preparation have been followed. Key points to keep under consideration are as follows:
  • Greige fabric construction should be planned so as it takes into consideration a 15 to 20% greige to finished fabric shrinkage.
  • Warp tension should be kept at a minimum. Usually slightly higher than the tension required to form a good shed opening. However shed height also needs to be considered and kept at a minimum in order to minimize the cyclic yarn tensioning during weaving.
  • A reed with the maximum Air space is also highly recommended as it reduces the yarn to yarn friction and the possible Velcro effect.
  • Weft yarn tension should be carefully controlled. In the case of the spun yarns in the weft, care should be given that the accumulator brushes are not stiff and abrasive.
  • Loom speed is also a variable that needs to be considered and adjusted to keep loom stoppages to a minimum. 
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