VASILICA POPESCU, IRINA CRINA ANCA SANDU, GABRIEL POPESCU COLORIMETRIC EVALUATION OF CHEMICAL MODIFICATIONS GENERATED BY PAN FUNCTIONALIZATION IN ACID/ BASIC MEDIUM AND GRAFTING WITH CHITOSAN
The acrylic fiber from Romania - Melana (PAN) consists in a tertiary copolymer obtained through copolymerization of three comonomers: vinyl-acetate (AV), acrylonitrile (AN) and Da- methyl styrene (MS). PAN functionalization depends on the reaction medium: a strongly basic pH converts the acetate group from AV in hydroxyl group, and the nitrile group from (AN) in COOH group via amide group. This thing does not happen in weakly acid medium realized with acetic acid (pH= 4-5). Yet, in this acid medium occurs the protonation of acrylic fiber, which confers the possibility of establishing electrovalent bonds between the fiber and a basic compound, such as chitosan. In this paper, one evaluates colorimetrically all the chemical modifications appeared on PAN during functionalization in basic/acid medium and then grafting with chitosan (CS). Dyeing operations with non-specific dyes (reactive dyes) were performed using different concentrations, durations and pH. By comparing the tinctorial behaviour of the acrylic supports in the two mediums (acid and basic), it resulted that functionalization through saponification determines important chemical modifications. Through grafting, the contribution of NH2 groups from CS makes possible dyeing in acid medium, a fact confirmed by the values of colour strength (K/S), as well as by the colour differences (DL*, Da*, Db*, DC*, Dh*, DE*).The chemical modification produced during functionalization and grafting have been proved by qualitative methods (FTIR analyses and dropping colour test) and quantitative method (dyeing with reactive dyes when the values of K/S and of colour differences can also highlight the impact of these modifications).