ALPATEC MG 2.1 Manual de usuario descargar pdf (Pagina 17)

UNITEX nr. 1 - 2014

Analysis of the results

Degree of whiteness

The degree of whiteness is improved as a result

of the reduction of the ash content of the cotton

by an additional pre-treatment step carried out in

the beginning before the actual bleaching process.

Calcium, magnesium, iron ions and other metal salts

are dispersed and masked in acid media and removed

nally by rinsing. If there is no separate pre-treatment

step before bleaching as it is the case with the

conventional peroxide bleaching, the water hardness

salts and catalysts affect the bleaching action and

lower whiteness levels are the result. So a better

stabilising of the bleaching bath would be essential.

The best degree of whiteness can be achieved by the

process combinations demineralizing and bleaching

(process B – Fig. 2 and 3) as well as pre-washing

and bleaching (process C – Fig. 2 and 3) where the

pre-treatment procedure takes place in two separate

baths. Also, excellent results could be achieved by the

OPTABLEACH procedure, which unites demineralizing

and peroxide bleaching in one economical pre-

treatment bath (Fig. 2: degree of whiteness).

ZSCHIMMER & SCHWARZ

MOHSDORF GmbH & Co KG

Textile Auxiliaries Division

process: amount of baths degree of whiteness

A) Conventional bleaching

process 

1 73,50 °Berger

B) Acid demineralizing and

separate bleaching

2 80,86 °Berger

C) Pre-washing and separate

bleaching



2 78,57 °Berger

D) OPTABLEACH 1 77,83 °Berger

Figure 2: Degree of whiteness

Figure 2: degree of whiteness

ZSCHIMMER & SCHWARZ

MOHSDORF GmbH & Co KG

Textile Auxiliaries Division

process: DP

[EWNN-method]

ash content

[%]

Greige fabric 1932 0.85

A) Conventional bleaching

process 

1650 0.30

B) Acid demineralising and

separate bleaching

1760 0.12

C) Pre-washing and separate

bleaching



1750 0.13

D) OPTABLEACH 1754 0.11

Figure 3: DP and ash content

Process time

The shortest process is the conventional standard

bleaching with 40 min at 98° C. Additional time for

lling, heating, cooling and draining must be taken

into account. These times depend on the respective

machine that is used and can only be estimated. The

OPTABLEACH process, too, takes considerably little

time requiring only 10 minutes more for demineralizing.

The process combinations demineralizing and bleaching

as well as pre-washing and bleaching take the longest

time because at least 20 minutes have to be added for

the rst treatment step.

Degree of polymerisation and ash content

The degree of polymerisation (DP) is the most important

factor for the evaluation of the quality of cotton goods.

It is the average number of monomer repeat units

contained in a cotton polymer chain.

Depending on the respective cotton quality, the original

DP is higher or lower. The level of the DP drop after

bleaching represents the extent of the bre damage

caused during the treatment.

Also the ash content of the fabrics is a good indicator

of the effectiveness of the process.

The conventional bleaching procedure without any

demineralization step leads to the highest bre damage

whereas the process combinations demineralizing and

bleaching (B), pre-washing and bleaching (C) and the

OPTABLEACH treatment (D) yield a higher DP and,

moreover, a lower ash content (Fig. 3: DP and ash

content).

This outcome is conrmed by pre-treatment operations

under practical conditions. The tensile strength of

cotton yarn in particular is improved signicantly.

Reproducibility

Practical tests with different cotton qualities have

shown that the application of the multiple step and

OPTABLEACH processes can not only improve the

degree of whiteness, but also that the level of the

results achieved is close to each other.

In contrast to a conventional bleaching procedure, the

bleaching effects are uniform to a high degree which,

consequently, ensures even shades in the subsequent

dyeing process (Fig. 4: reproducibility).

ZSCHIMMER & SCHWARZ

MOHSDORF GmbH & Co KG

Textile Auxiliaries Division

Figure 4: Reproducibility

•

  Higher degree of whiteness (°Berger)

due to demineralization

•

  Less variation of whiteness

for a better reproducibility

with demineralization - OPTABLEACH

without demineralization

greige fabric

CO jersey

peroxide bleach

on greige fabric

demineralization

+ peroxide bleach

6 different qualities of CO knitwear

OPTABLEACH benefit: One-bath system including a demineralization treatment

Figure 4: reproducibility;

OPTABLEACH benet : one-bath system including a demineralization treatment.

pH value

The pH value of the treatment liquor generally depends

on the process water used. Our tests have shown that

a strongly acid pH value below 3.0 is not necessary in

order to reach acceptable demineralizing effects.

A pH value of around 4.0 turned out to be sufcient

which is automatically adjusted when phosphoric acids

are used. Strong acids such as sulphuric acid shall not

be used anymore since they will damage cotton bres

which results in a lower DP.

The pH value rises about 1 to 1.5 points during the

demineralizing process due to the sequestration of

the iron and alkaline earth metals. So only a very little

amount of caustic soda is necessary for neutralising.

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