copolymerization of pretreated kraft lignin and acrylic acid to produce flocculants for suspension and solution systems
abstract
the presence of dyes in the wastewater of textile industry poses a number of environmental
concerns due to their toxic nature and the removal of dyes from the wastewater is a major challenge
nowadays. synthetic polymers are commonly used in the flocculation of various colloidal systems.
however, these synthetic polymers cause environmental concerns due to their nonbiodegradability
and toxicity to human and animals. their high costs also limit their use in many
applications. these disadvantages may be overcome by using polymers derived from natural
sources. lignin is the most abundant renewable resource after cellulose, and is an inexpensive raw
material that can be used to produce high-value products, such as flocculants, dispersants, phenols
etc. native lignin does not possess suitable properties to be used as is, however, its attributes can
be changed by means of chemical modifications. in this thesis, kraft lignin was initially modified
via sulfation, sulfomethylation or phenolation methods and subsequently copolymerized with
acrylic acid. the resulting copolymers were characterised using a variety of methods including
nmr, ftir, tga, molecular weight analysis, and elemental analysis, all of which demonstrated
remarkable changes in the chemical and physical structure of lignin after modification. the
flocculant property of the produced copolymers was investigated in alumina suspensions via
studying a) the adsorption behaviour of copolymers on alumina particles b) changes in the zeta
potential of alumina particles, and c) the ability of the copolymers to alter the relative turbidity of
alumina colloids. the results demonstrated that the copolymers could indeed act as effective
flocculants, with their performance being partly dependent on their charge density, molecular
weight and their ability to decrease the zeta potential of the alumina particles. indeed, the
copolymers with the highest charge density and molecular weight adsorbed more dye. this work
demonstrated the potential of using widely available, inexpensive, and renewable kraft lignin as a
flocculant after modification. it also provided information on the flocculation of ethyl violet dyes
from synthetic solutions. the data also provides further information about the mechanism and best
ways to chemically modify lignin, as well as how these products function as flocculants.