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- Practical Guide -
Page 114 of 153
ANNEX I TO SECTION 5 OF CHAPTER I
REMARKS CONCERNING THE DETERMINATION OF THE
VARIOUS PERCENTAGE OF "CELLULOSE", "SOFTENERS" AND
"OTHER ADDITIVES"
Warning:
This is a document prepared by CIPCEL and transmitted to the Commission services on
21 April 1992. It should not be considered as a Commission document.
In the industrial manufacture of regenerated cellulose film (RCF), three main stages can be
identified:
(a)
Production of viscose (cellulose xanthate dissolved in sodium hydroxide solution).
(b) Coagulation of the viscose and regeneration of the cellulose from the cellulose xanthate.
The resultant film is washed and the necessary additives incorporated. This is followed
by controlled drying to provide an uncoated film.
(c)
To provide additional properties (heat sealability, controlled water vapour
permeability.....) to the cellulose film, the latter is often coated with lacquers based on
cellulose nitrate, polyvinylidene chloride or polyvinyl chloride/acetate copolymers.
The colorants referred to in Article 2, paragraph 2, can consist of
-
Pigments (e.g. titanium dioxide, iron oxide) introduced into the viscose, stage (a)
-
Organic, soluble dyes, incorporated into the wet cellulose film, stage (b), or into the
coating, stage (c)
Analytical precautions
When the percentages of "cellulose", "softeners" and "other additives" in an uncoated and/or
coated cellulose film are measured, corrections have to be made for the various constituents
(see later) It should also be noted that the presence of colouring matter (pigments or dyes) can
interfere with some analytical procedures.
In order to measure the water content in the film (which varies with atmospheric humidity),
direct drying must be avoided, as this may induce errors in the analysis through the loss of
relatively volatile components.
It is recommended that several specimens of a sample be conditioned in the same manner
(temperature, relative humidity and time). Some of them are used for the determination of the
water content, e.g. according to Karl Fischer, while the others are used for further analyses.
Let W% be the water content of the film.
The amount of lacquer applied to the uncoated film (L%) is determined by a suitable
technique, such as by spectrophotometry, back-scatter or an appropriate extraction method,
using the conditioned specimens.