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                        APPLICATION OF CHITOSAN AS SIZING AGENT

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                        Sizing agents -Application and problems

                        The weaving process poses a great challenge to warp yarns due to high rubbing forces caused by harness and threads nearby. To endure this stress without damages it is usually necessary to cover the warp yarn with a protective coat – what means to size.

                        However, as the layer of the protective size impairs the subsequent finishing of woven fabric, the size has to be removed after weaving (desizing) and reaches the waste water. Thus, the final elimination of the size has to be made in waste water treatment plants.

                        Today‘s widespread high-capacity weaving machines make very high demands on the warp yarns processed. In order to realize high weaving speeds without thread breaks or yarn raising, sizes based on starch mostly used in former times do no longer suffice.

                        In case of natural fibre spun yarns starch based sizes are combined with additives made from polyacrylate, polyvinyl alcohol or polyester. The sizes for synthetic fibres are mostly based only on these products or on combinations thereof. Thus the major part of sizes used for common fibre types consists of non renewable, fossil raw material.

                        Such synthetic sizing agents are biologically degradable to a certain limit only. In principle, a recycling of the size is possible by recovery, however, this calls for the fact that the size which was separated before during desizing can be reused in the same factory for sizing of warp yarn. GGiven that such vertical structures are rather uncommon in today‘s textile industry, the search for high-capacity biologically well degradable sizing agents is recommendable.


                        Chitin and Ch itosan

                        B esides to cellulose, chitin is the most frequent polysaccharide on earth. It is one of the few quantitative significant renewable raw materials. In nature chitin is used for building up of structures and is contained in the shells of shellfish or in mushrooms.




                        Chitin – which is widely available as a byproduct (for example out of crab shells) – serves as raw material in the production of chitosan. However, the transition of chitin into chitosan is a smooth process. If there are more amino groups than acetamido groups in the whole molecule (degree of deacetylation > 50 %) the substance is called chitosan.




                        Apart from the degree of deacetylation, the molecular weight is also a decisive factor for the quality of chitosan and strongly influences the properties of solutions made of it.

                        Both, the powdery chitin/chitosan blend as well as solutions made of it, are very good biodegradable.


                        Results of our trials

                        We tested a range of chitosan qualities regarding their applicability as sizing agent and found that certain qualities show a good adhesive power and a good water solubility. Apart from these basic requirements for sizing agents there are further reasons predestinating chitosan to be used in this area:

                        - chitosan is soluble in diluted strong acids (except of sulfuric acid) and organic acids

                        - chitosan forms a film and is gas permeable

                        - in dissolved condition chitosan is colourless

                        O ur trials showed that warps sized with chitosan do not have any disadvantage regarding processability compared to warps sized with common agents. But how does the use of the new raw material influence the following process steps? In our trials for clarification of this question we analysed the desizing of warps as well as the behaviour of not desized warps during bleaching, dyeing and further steps of finishing (resin finish, water repellent finish, etc.). We could not find any disadvantageous influences of chitosan sizing agents for subsequent process steps.

                        The results obtained so far show that the future of chitosan derivates applied as sizing agents seems to be exceedingly interesting.


                        perspective

                        The first steps have been taken. Chitosan sizes offer an excellent possibility to substitute processes based on mineral oil by processes based on renewable raw materials. If you like to go further on this way, we will be pleased to come along with you in all technical issues.


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