2.3.4 Hydroxyalkylated guar gum
Hydroxypropyl guar (HPG) is first commercially
synthesized guar ether in 1960 by General
Mills Inc USA. Hydroxypropyl guar (HPG) is
mostly used in oil drilling industry. It has
numerous applications in paper/textile industry
as sizing agent and pigment printing thickener.
Boonstra et al.prepared non lumping
hydroxyalkylated guar derivative with DS value
of 0.12 to use as a thickener in textile printing.
O-(2-hydroxyethyl), O-(2-hydroxypropyl), O-(2-
carboxymethyl) guar gum derivatives were
prepared by H .prabhanjan et al.with variable
reaction parameters. Rate of hydration,
rheological behaviour, viscosity, moisture
contents of resultant products were analyzed.
Rheological behaviour of hydroxyethyl guar
(HEG) and hydroxypropyl guar (HPG) and its
derivatives was studied in detail by Lapasin et
al.under continuous and oscillatory shear
flow rate. They summarized that molecular
weight and amount of polymer has visible effect on rheology of gum along with
temperature. Rong Chun Xiong et al.78
developed novel route for synthesis of
hydroxypropyl guar by phase transfer catalysis.
Typical procedure involves the reaction
between guar, propylene oxide and HTAC
(hexadecyl trimethyl ammonium chloride) as
phase transfer catalyst. Results disclosed that
modified guar has higher viscosity, stability and
light transparency as compared to native one.
G.Wang et al.improve biocompatible sol-gel
silica matrix for the encapsulation of drugs by
incorporating a novel water soluble silica
precursor, tetrakis(2-hydroxyethyl)
orthosilicates (THEOS) and outcome verified
rapid sol-gel transition of THEOS in water
without any addition of organic solvent and
catalyst. Determination of the degree of
substitution of Hydroxypropyl guar gum
(HPGG) was studied by Yannan Chen et al.
by pyrolysis of gum at C6 position. Gas
chromatography and GC-MS spectrometry was
employed for investigated DS of subsequent
products. A new chemical method was
introduced by Xiaoyan Wua et al.to
determine substitution pattern of hydroxypropyl
guar. A novel method involve periodate
oxidation of gum and product was investigated
by IR and NMR techniques. A novel derivative
of guar gum hydroxyethyl amino hydroxypropyl
guar gum (EAHPG) was prepared by Y. Zhao
et al.by chemical modification of ptoluenesulfonate
activated hydroxypropyl guar
gum with ethanolamine through nucleophilic substitution reaction. Results were confirmed
by FTIR and NMR spectroscopy.