Flocculation is a process of
bringing together smaller particles to form larger particles, and settling of
colloidal particles from stable suspensions caused by the addition of chemicals
known as flocculants in minute quantities Bratby , George .
There are two types of flocculants polymers depend on their
sources, Synthetic organic flocculants: these are based on various monomers
like acrylamide, acrylic acid, diallyldimethyl ammonium chloride (DADMAC),
styrene sulphonic acid etc. Natural organic flocculants: these are based on
natural polymers like starch, cellulose, natural gums and mucilages and their
derivatives Sharma et al 2006.
Among the polymeric flocculants, the synthetic polymers can be tailor-made by
controlling the molecular weight, molecular weight distribution, chemical
structure of polymers, and nature and ratio of functional groups on the
polymeric backbone. Due to versatile tailorability, synthetic polymers are very
efficient flocculants. However, they are not biodegradable and shear-resistant.
Natural polymers, mainly polysaccharides, are moderately efficient, are
shear-stable, biodegradable, and inexpensive Singh et al 2000.
Water-soluble polysaccharides have myriad industrial and agricultural
applications. It can be successfully used as flocculants Bolto.BA 1995 , Polysaccharides
have various characteristics. They are biodegradable, shear-stable,
inexpensive, and easily available from renewable farm and forest resources.
Depending on the source, these poly-saccharides may have many
low-molecular-weight impurities. The biodegradability of polysaccharides reduces
their shelf life and needs to be suitably controlled. In various applications,
their required dosages are large and their solutions and flocs lose stability
and strength because of biodegradability. However, it could be modifying by
grafting synthetic monomer Nayak
& Singh 2001 and cationization Singh et al 2009.
Many earlier researches have been made to combine the best
properties of both by grafting synthetic polymers onto the backbone of natural
polymers after purification Deshmukh
et al 1991 , Ungeheuer et
al 1989. The advantages gained
from the earlier studies were the consequent reducing of biodegradability and
high shear-stability Morgan &
McCormick 1990, Singh 1995.
Bigand et al extensively study the cationization of xylan or
glactomannan ( guar ) by using 2,3-epoxy propyl trimethtyl ammonium chloride as
etherifying agent under alkaline condition. Reaction condition were optimized
to obtain a derivative with maximum DS value, they success to obtain 1.3 DS
value and 48% grafting rate.
Pang et al 2013 synthesize a novel organic polymeric flocculant by
grafting cationic etherifiying monomer 3-choloro-2-hydroxy-propyl trimethyl
ammonium chloride (CHAPTAC) onto the backbone of concorb powder. The synthetic
reaction was initiated by hydroxyl radical made from Fenton reagent (H2O2- FeSO4).
The synthesized cationic polymer shows superiority as a novel flocculant.
Lu et al 2004 develop initiation system by adding persulfate to
cerium ion, This results successful synthesis of a graft co polymer of starch
with acryl amide (AM) and diallyl dimethyl ammonium chloride (DAMAC) when the
cationic degree was 22%.
Mclean et al 2011 synthesize guar gum- graft poly ( AM-co-DAMAC )
by using Lu et al 2004 method , The percentage of grafting was 85% and the
grafting efficiency was 79.16%.
Rezali et al 2012 study the process optimization of grafting DAMAC
monomer onto cassava starch backbone using cerium nitrate free radical
initiator without persulfate and they got 14% cationic degree.
Singh et al 2004 work in developing microwave assisted synthesis of
guar- g-poly acrylamide, Their work results very short reaction time and high
grafting efficiency 66.66% in just 0.22 min.
Acacia gum (Arabian gum)
Acacia gum is a natural arabinogalactan-protein type polysaccharide
widely used in industrial applications. The two varieties of Acacia gum, acacia
senegal and acacia seyal, are hyperbranched polysaccharides rich in arabinose
and galactose . senegal presented the highest degree of branching 78.2 % compared to
59.2 % for seyal Lopez-Torrez
et al 2015.The weight average molecular weight of acacia seyal is at
least three times greater than acacia senegl, The average molecular weight of
acacia seyal species is between 1.7 * 106
to 2.1 *106 compared to 0.6*106 for acacia SenegalHassan et al 2005.