Methacrylate monomers for Polymeric Additives
Silk, like wool, is a protein-based fiber. Under standard climate conditions (65% relative humidity) the water uptake is 11% – it can climb up to 30% without feeling wet. The particular sheen and texture of silk comes from degumming the raw silk prior to dyeing and weaving. Degumming refers to the removal of the silk gum (sericin) that encloses the raw silk threads. Depending on origin (mulberry silk or tussah silk) and on the degree of degumming, weight loss ranges between 2% and 30% of the raw silk weight – at a simultaneous loss of fiber strength in the order of 20%.
The weighting process compensates for the weight loss from degumming. In the past, tannins (tannin or gall nut extracts) or minerals, such as metal salt solutions, were mainly used for weighting. Extensive studies have shown that chemical weighting of the silk fiber with VISIOMER® MAAmide (methacrylamide) delivers key benefit, especially for necktie manufacturing.
Silk weighting with VISIOMER® MAAmide is a thermally initiated graft polymerization process, starting with an aqueous solution. Generally, the degummed raw silk is stored for two hours at temperatures of 50-70°C, with stirring in various concentrated aqueous methacrylamide solutions and the addition of 0.1% ammonium persulfate. In practice, the ratio of methacrylamide employed is a useful indicator for determining the desired degree of weighting. Weighting and graft yield decrease as graft temperatures rise. The graft (reaction) temperature to be selected is therefore yet another significant parameter for adjusting the degree of weighting.
Besides VISIOMER® MAAmide, VISIOMER® HEMA and/or HPMA can be used for silk weighting to modify the properties of the weighted silk.