Utilization of biopolymer for screen printing of silk with natural dyes
Abstract
Dyeing and printing with natural dyes are age old crafts and require artistic skill to develop colours and
patterns on fabric using certain techniques. In lieu of synthetic dyes and changing market trends, the demand for
natural dyed/printed products diminished. However, with stringent environment regulations and increasing interest
of consumers, the use of natural dyes and biopolymers for textile processing is gaining momentum. Natural dyes and
biopolymers or their combination can be applied on the textile fabrics to obtain varying colour or shade to increase
the dye uptake and improve the colour fastness behaviour of any natural dye. Hence, the present study was
undertaken to replace the metal based mordants and promote the use of biopolymers for textile printing. Chitosan
biopolymer with five different natural dyes was explored to assceratain the effect of biopolymer mordanting in
screen printing of silk fabric. Prior to biopolymer treatment the enzymatic degummimg of silk fabric was carried out
using a combination of protease and papain enzymes (75:25) to improve its wettability. On the basis of visual
evaluation and wash fastness towards change in colour (CC) and colour staining (CS), chitosan biopolymer and two
natural dyes were selected for screen printing of silk fabric. To prepare the printing paste of selected natural dye
extracts, two thickeners namely guar gum and gum acacia were tried. On the basis of visual evaluation and wash
fastness grades, one thickner was selected. The different variables of printing receipe viz. biopolymer concentration,
mordanting method, dye extract concentration, dye extract: thickener ratio and fixer concentration were optimized on
the basis of visual evaluation and wash fastness properties (CC and CS) of screen printed silk fabric samples. The
silk fabric was screen printed as per optimized variables of printing receipe. For biopolymer mordanting and screen
priniting of silk fabric with natural dyes, chitosan biopolymer along with indigo and lac dyes were selected on the
basis of visual evaluation and wash fastness (CC and CS) grades of screen printed silk fabric samples. The guar gum
thickner was selected to prepare the printing paste of indigo and lac dye extracts. The optimized variables viz. 15
percent concentration of chitosan biopolymer, pre mordanting method, 5 and 6 percent concentration of indigo and
lac dyes respectively, 1:2 ratio of dye extract: thickener and 4 percent concentration of acrafix fixer were used for
screen printing of silk fabric. The colour coordinates in terms of L*, a*, b*, C*, H* values and colour strength (K/S)
of chitosan biopolymer mordanted and indigo and lac dyes printed silk fabric samples reflected the improvement in
colour properties of biopolymer treated printed silk fabric samples as compared to unmordanted printed and alum
mordanted printed samples. The colour fastness properties towards wash, light, perspiration and rubbing of chitosan
biopolymer mordanted and indigo and lac dye printed samples ranged between good (4) to excellent (5) which were
observed to be higher in comparison to unmordanted printed and alum mordanted printed samples. Priliminary
properties i.e. fabric count, weight and thickness of chitosan biopolymer mordanted printed samples exhibited an
increase in these properties. The physical properties studied in terms of bending length, tensile strength, elongation
and performance properties i.e. crease recovery angle and functional properties viz. UV protection and antibacterial
activity of chitosan biopolymer mordanted and indigo and lac dyes printed silk fabric samples expressed an increase
in these proeprties when compared with unmordanted printed and alum mordanted printed silk fabric samples. It is
thus concluded that pre mordanting of silk fabric with chitosan biopolymer for screen printing with indigo and lac
dyes enhanced the depth of colour, sharpness of print, evenness of print, overall appearance of print and colour
properties, colour fastness to various agencies as well as physical and functional properties of screen printed silk
fabric samples. Hence, chitosan biopolymer can be successfully used as viable approach to replace the conventional
metal based mordants.