FORM 2

THE PATENTS ACT, 1970

(39 of 1970)

The Patents [Amendments] Rules, 2006

COMPLTE SPECIFICATION

(See section 10 and rule 13)

GRANTED PATENT No. 274671

AGRO BASED ADHESIVE FOR PLY-WOOD AND

OTHER WOOD COMPOSITES

Hindustan Gum & Chemicals Limited

Birla Colony,

Bhiwani - 127021

Haryana, India

Incorporated under the Companies Act, 1956 (Act No. 1 of 1956)

with registration no 25301 dated 15/2/1962

The following specification particularly describes the invention and the manner in which it performs:

AGRO BASED ADHESIVE FOR PLY-WOOD

AND OTHER WOOD COMPOSITES

Technical Field of Invention

The invention relates to the field of agro protein based adhesives and their compositions that find

use in the preparation of ply-wood and other wood composites in partial or whole replacement of

synthetic resins.

Background and the Prior Art

Urea-formaldehyde (UF) based thermoplastic resins have long been used in the production of

different types of ply-wood and other laminated wood composites for interior and exterior

applications. For ease of customization and low cost, UF resins have been preferred choice by

the ply-wood industry that offers much required excellent binding and water resistant properties

to the final products.

Despite high acceptability of UF resins by manufacturers of wood products, there is considerable

concern of its use in domestic and commercial environments for reasons of public health. This

concern is on account of the fact that wood products using UF resins tend to emit small amounts

of toxic formaldehyde gas over a long period of time. Since prolonged exposure to these toxic

emissions is injurious to public health, the use of such wood based products, especially in interior

environments is a subject to regulatory compliance in many countries.

The above concern of formaldehyde emission found expression in US4282119 that describes an

invention for preparation of wood composites using minimal quantity of the formaldehyde resins

in the adhesive formulation.

Rising cost of UF resins is yet another reason for search of alternative adhesives for application

in wood industry that are affordable and environmentally benign with low or no toxic emissions,

especially for indoor environments. The quest for environment-friendly products in this industry

led many researchers to look for raw materials from renewable resources while keeping

performance and price at favourable levels. A number of protein rich compounds from natural

resources such as, casein, animal blood and soy proteins are reported to have been developed

and used in place of UF resins to make high performance wood adhesives.

US3153597 describes the application of caseins for wood adhesives. Self curing glue by

reacting a polymeric dialdehyde such as commercially available per-iodate - oxidized dialdehyde

starch or dialdehyde cellulose with casein has been developed. It is claimed that the plywood and

other wood composites prepared by this type of adhesive have higher shear strength and

weather resistant properties. The drawbacks in this process are i) uncontrollable viscosity of the

adhesive since treatment of casein with dialdehyde considerably increases the viscosity and

makes the application of adhesive in wood products difficult, ii) the wood products get stained

with rich tannic acid.

US20100018436 disclosed the use of animal blood for making adhesive for plywood and

laminated wood products. Fresh blood has been used without dewatering it and different

modifiers such as anticoagulant, preservatives added with lime to adjust the pH of the adhesive

in between 9-11. A curing agent has been used to cure the adhesive during processing condition.

Blood protein based adhesives are reported to have higher moisture resistance, but poor shear

strength than the casein based adhesives.

A number of previous US patents, viz., US1976436, US 2400541, US2874134 cited in the above

patent described various methods of making adhesive suitable for plywood, all of which require

the blood to be dewatered and dried before processing making the process unviable. In

US4180412, the blood is pretreated with an anti-coagulant. US4333767 describes method of

making blood-based glue from sprayable blood that had been previously dried.

Thus, several animal blood based adhesives are reported in patent literature but none of them is

known to be in commercial use, presumably because all known processes required blood to be

dried before use as a raw material for preparation of adhesive. US20100018436 is a relatively

recent one and does not require dehydration and thus seems to have potential in reviving the

interest in blood-based adhesives.

Among the proteins, obtainable from agriculture sources for making adhesives for plywood or

other wood composites, soybean protein has received much attention. Soy protein was used as

an adhesive for plywood in the early

1900s

(US1813387 and US1724695) even before

petroleum-based UF resins became popular due to their easy availability, and excellent

performance. Environmental considerations due to formaldehyde emission over long periods are

once again turning the attention of researchers back to soy and other agro-based proteins.

US20020005251 describes improved adhesive binder prepared from soy protein by reacting with

different modifiers for application in the wood products essentially to replace commonly used UF

resins. It is stated that due to its bio origin and from an abundant renewable source, the soy

protein based adhesive is environment friendly, and hence preferable than petroleum based

adhesives. The preferred modifier in the above patent application is ‘guanidine hydrochloride’ as

per the granted patent US 6497760.

Nonetheless, the soy protein adhesives, except the formulation as given in US6497760, hitherto

available lack required properties of gluing strength and water resistance, these have, by and

large, failed to become popular. There is, therefore, a felt need for developing more potent agro

based protein adhesives that are more potent than those known in the prior art. The known

shortcomings are now addressed by this invention of modified soy protein based adhesive.

US20080021187 describes an improved method for the production of soy based adhesive by

denaturing the protein by the treatment with urea. Heat treatment has been employed in this

invention for the denaturing the protein prior to addition of urea. This process has been stated to

result in to the increased stability and strength of the resultant adhesive prepared from denatured

protein.

US7081159 describes a soy protein based adhesive formulation using zinc sulphate

heptahydrate as cross linking agent where soy protein isolate has been used as a source of soy

protein. A number of inorganic and organic compounds have been included in the formulation to

impart better stability and binding strength. However, the soy protein isolate is more expensive

as compared to the common soy protein or soy flour.

Soy flour / protein based adhesive has attracted the attention of many researchers for obvious

reasons for application in wood composites made with such adhesives. Most of these

formulations have thus far offered low shear strength and poor moisture resistance as compared

to formaldehyde based synthetic resins. Nevertheless, a search for high performance adhesive

based on agricultural resource for wood applications continues to be on the wish-list that has the

potential to replace UF resin for such applications.

US4282119 describes the preparation of wood composites made of urea-formaldehyde or urea

melamine formaldehyde resins. The use of formaldehyde resins has been minimized to the

extent possible to control the resultant emission of formaldehyde in the final end products.

US3268460 describes preparation of adhesive for wood industry from phenol aldehyde and uses

small amount of guar or casein as additive.

WO2007017590 describes guar protein extract product and method for the production and uses

thereof which is a PCT application designating more than 100 countries and regional offices of

EAPO, EPO, ARIPO, and OAPI. This invention relates to cosmetic or pharmacological or plant

protective compositions or to domestic care agents based on modified guar protein extract and

methods for the production thereof.

We, however, report herewith hitherto unreported agro-based adhesive compositions based on

protein obtainable from sources other than soy and casein, particularly guar and others that are

commonly found in India for ply wood and wood composites industry that can replace expensive

and toxic synthetic ingredients, urea-formaldehyde resins.

OBJECTIVE OF THE INVENTION

The main objective of this invention was to develop a high performance adhesive for application

in wood industry from guar protein, a bye product of guar gum manufacturing that has

comparable or better performance with commonly used UF resins in terms of binding properties

and low moisture susceptibility.

SUMMARY OF THE INVENTION

The guar protein, a bye product of guar gum manufacture has been deployed to produce an

adhesive suitable for wood applications. The guar protein obtained as a bye product from the

process of guar gum manufacture, is denatured through a series of chemical reactions in a

controlled manner.

The denatured guar protein is then cross-linked by addition of a suitable cross-linking agent in its

aqueous solution. The denaturing of guar protein and subsequent cross-linking with suitable

cross-linking agents are central and key steps in developing guar protein based adhesive

composition and resin. The cross-linked guar protein can optionally be mixed with suitable

extenders and viscosifiers to impart different characteristics to adhesive composition that can be

employed for preparation of ply wood and other wood composites in place of commonly used UF

resins.

The guar protein based wood adhesive of the present invention provides a high performance

wood adhesive as an alternative to the synthetic resin based adhesives and can be regarded as

‘green technology’. The wood composites manufactured from the guar protein based adhesives

can be used for both interior and exterior applications.

STATEMENT OF INVENTION

A heightened concern on human health and environment due to slow and continuous

formaldehyde emissions from urea-formaldehyde resin based adhesives used in wood products

over long periods of time necessitated to look for environmentally benign alternatives to UF

resins.

A range of agro-based protein rich renewable resources such as casein, animal blood, soybean

protein, etc have attracted the attention of researchers to develop alternative adhesives.

For the first time, we report an invention based on guar protein that is a bye product of guar gum

manufacture, a large scale production and export of which takes place from India and many other

countries around the world. A process of preparation of high performance adhesive based on

guar protein as well as its composition for use in wood applications is disclosed.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING(S)

Having thus described the invention in general terms, reference will now be made to the

accompanying drawings wherein:

FIG. 1 shows a general scheme of reaction sequence for preparation of guar protein based

adhesive composition and resin through three main steps

FIG. 2 shows a schematic diagram for preparing denatured guar protein, an essential step in

making the adhesive composition / resin

FIG.

3 shows the arrangement and the face / core veneers used in making the

6 mm

experimental ply for evaluating the bonding strength of glue composition with denatured guar

protein of this invention

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a high performance adhesive composition produced by chemical

and physical modification of guar protein in the presence of alkali and urea that is used with

suitable cross-linking agents in the final application for adhesion in the plywood industry through

various steps as described in Figures 1 and 2.

The guar protein is a protein rich bye product obtained from the guar seed. Guar seed is

composed of a pair of tough, elastic endosperm sections, referred to as “guar splits” between

which is sandwiched brittle embryo (germ). The germ section is a rich source of guar protein. The

entire structure is confined in a tough seed coat referred to as hull. The seed is broken into two

halves by mechanical attrition (a well known technology of guar seed processing). The protein

rich germ is separated during this process. The purified guar splits prepared through multi-step

process are subjected to milling to obtain guar gum powder of different grades.

The guar seed contains about 28-35 % galactomannan polysaccharide and 45-60 % pretentious

material. The split is reported to contain nearly 80 % galactomannan with minor amount of

pretentious material, inorganic salts, water insoluble fiber etc. The process of producing pure

guar split and the protein rich bye product are well-known and form part of the contemporary guar

gum technology.

The ’guar protein’ obtained as a bye product in guar gum technology is the basic raw material for

the invention disclosed herewith and comprises nearly 45% by weight of protein content. The

protein content in this starting raw material is determined by measuring the nitrogen content by

standard Kjeldahl method for nitrogen estimation. The remaining portion of guar protein

additionally contains small amount of galactomannan polysaccharide, oil, water, sugar unit, fiber

and minerals. The protein part is known to contain wide varieties of amino acids, principally

glutamic acid, arginine, aspartic acid, lysine, cystine, tyrosine, histidine, serine, proline and

several others in small amounts.

The isolated guar protein obtainable in dry form (with small amount of moisture content to the

extent of up to 5-7%) as a bye product from the guar gum manufacture is used for conversion to

the adhesive composition directly or after milling it to form a powder.

Step 1: The first crucial step in conversion of ‘guar protein’ to adhesive composition or a resin is

denaturing of the protein as shown in Figure 1. The ‘guar protein’ (A) is denatured using a

suitable ‘denaturing agent’ (B) in presence of a suitable plasticizer (C), where:

B = urea, guanidine hydrochloride, heat, acid, alkali, alcohol, sound waves of appropriate

frequency or a combination of any of these agents, and

C = plasticizer of the type of polyhydric alcohol, e.g., 1,6-hexane diol; 1,4-butane diol; 1,3-

propane diol; 1,2-ethane diol; 1,2,3-propane triol (glycerol) etc.

At the end of denaturing step, the pH of the reaction mass is lowered to about 7 by adding

inorganic or organic acid. The inorganic acid may my hydrochloric acid, sulphuric acid or nitric

acid of appropriate concentration. The organic acid may be acetic acid, phosphoric acid, fumeric

acid, citric acid or any other organic acid.

The guar protein when denatured unfolds from its native coiled structure thereby exposing the

functional groups like -COOH, -OH,-SH, -NH2 of the protein backbone available for cross-linking

in the subsequent steps. It is an important step in the process and needs to be carried out with

extreme care to avoid excessive denaturing since that can result into significantly reduced pot

stability and adhesive strength of the final product.

The property of plant based proteins to exhibit unfolded structures when denatured is well known.

This has been gainfully exploited in the prior art with regard to proteins obtained from soy, e.g., in

US 6497760. We have used this insight with regard to protein obtained from guar in this

invention. The unfolded protein structure helps enhance the contact area of functional sites

thereby increasing the much needed adhesion and bonding strength. An excellent insight into the

effect of different denaturants, viz., sodium dodecyl sulphate

(SDS), urea and guanidine

hydrochloride on guar protein fractions has been provided through observations on sedimentation

velocities, viscosities, ultra-violet and florescence spectra by Nath JP et al.1. The optimum

denaturing in this invention, however, is achieved by standardization through trial of various

batches with different denaturants under varying conditions.

While the reaction sequence of conversion of the guar protein to the adhesive composition and

resin through the crucial denaturing step is shown in Figure 1, the manufacturing scheme for the

denatured protein in a batch reactor following the unit operations of neutralization, cooling,

drying, sifting and homogenizing etc. are shown in Figure 2.

Example:

An example of working the Step 1 is given below to demonstrate the performance of the invention

without limiting its overall scope as already described above.

About 100 kg of guar protein is first charged into the reactor and mixed with small amount of a

suitable plasticizer thoroughly. A suitable denaturant or a mixture of denaturants, such as caustic

soda and urea etc. in about 10-15% of the mass of guar protein in an aqueous solution is then

slowly added. The mixture is then heated to between 30-950C over a period between 1-9 hours.

The reaction mass is then cooled to room temperature following which it is neutralized with 50%

sulphuric acid solution. A final reaction product containing denatured guar protein in semi-solid

state in about 110 kg is then obtained.

1 Nath* JP and Rao M.S Narasingha, Effect of denaturants on the 11S protein of guar seed ( Cyamopsis

tetragonoloba), J. Biosci., Vol. 5, Number 3, September 1983, pp. 209-217.

The reaction mass is then dried, pulverized and stored in cool and dry place for further use.

The characteristics of denatured guar protein produced by the above method are shown below in Table 1:

Table 1

S.No.

Parameter

Value

Viscosity 20% w/v at 25 ⁰C measured

2000 cps

by Brookfield viscometer

(approx)

Moisture content (%)

pH (20% w/v solution)

ca.7

Particle Size (passes thro’ 100 mesh)

90%

It may be noted that alkali, urea and heat together act as denaturing agents in this example. In

practice, however a variety of combination of denaturing agents could be employed to get the

right and optimum conformation of the denatured protein structure adjudged so by visual

appearance as well as the performance of the converted product.

Step 2: The next step in the process involves blending of (denatured) guar protein (D) with

suitable extenders (E1) and viscosifiers (E2) to make adhesive composition (F) as shown in the

Step 2 of Figure 1, where

E1 = any food grade or industrial grade maida^α, ground nut cake powder, coconut shell powder,

etc. The extender is used to provide required thickness and flow to the aqueous solution of

the adhesive composition, and

E2 = guar gum, pre-gelatinized and gelatinized starch, cassia gum, tamarind kernel powder etc.

^αMaida is a finely-milled wheat flour of less than 200 mesh per sq inch commonly used for making variety of breads

in India and other Asian countries.

Suitable quantities of the extenders (E1) / viscosifiers (E2) may be added to the denatured guar

protein (D) in accordance with the desired requirement of the thickness and flow of the solution of

resultant composition (F). Thus, different grades of guar adhesive composition (F) can be

prepared for various end applications keeping in mind the processability and binding

performance.

The extender is used to provide required thickness and flow to the aqueous solution of the

adhesive composition, and the viscosifier is added to increase the viscosity of the solution and to

provide a smooth spreading of the aqueous solution of the adhesive composition on the surface

of the ply. Appropriate commercially available preservatives could be added to the adhesive

composition powder or its aqueous solution to avoid microbiological growth during storage.

The adhesive compositions of the present invention have been developed for specific application

for ply-wood, laminate board and other wood composites essentially as replacement of

environmentally sinister urea-formaldehyde resin.

Step 3: The last and the third step in the process is basically a pre-processing step in the end

application. The denatured guar protein (D) or adhesive composition (F) as shown in the Step 3

of Figure 1 are allowed to react with suitable cross-linking agents (G) to produce adhesive resin

(H) which directly finds application in ply-wood industry or similar applications. In the step 3:

G = formaldehyde containing cross-linking agent such as formaldehyde, urea formaldehyde,

phenol-formaldehyde, resorcinol and melamine or a combination thereof

formaldehyde free cross-linking agent of isocyanates such as polymeric methyl diphenyl

diisocyanate

(pMDI), amine-epichlorohydrin resins such as polyamidoamine-

epichlorohydrine (PAE), epoxy, aldehyde, zinc sulphate hepta hydrate and / or urea based

resins

A variety of cross-linking agents can be employed in this step. However, formaldehyde free

cross linking agent within a favourable cost - performance envelope is desirable to meet the

objectives of minimizing toxic emissions of formaldehyde in this invention.

Binding Performance of Denatured Guar Protein Based Adhesive Composition / Resin

The Step 3 is an important step before the denatured guar protein (D), the main product of this

invention and / or its marketable adhesive compositions (F) for variety of end applications to

impart necessary adhesion. Experiments below are described to demonstrate the use of this

invention and its superior performance as compared to the industrial resins of the prior art

available commercially. These also demonstrate the environmental-friendly characteristics of the

products of this invention.

An aqueous solution of the powder (as obtained in Step 1 or in Step 2) is reacted with a suitable

cross-linking agent to make the adhesive resin. The choice for type and amount of cross-linking

agent used for making the resin in this invention depends on several factors such as the pot life,

cross linking rate, cost of the adhesive product, as well as on the nature and characteristics of the

denatured guar protein making available cross-linking sites. The cross-linkers used in the

experiments below are with a view to demonstrate the use of this invention and do not limit the

scope of its use with other possible cross-linkers imparting desired cost-performance advantage.

Experiment 1

An aqueous solution of the 10 kg of denatured guar protein is mixed with 60 kg of water and 10

kg formaldehyde (35% solution) to form a homogenous slurry that is directly used in making a

standard 12 mm thickness of commercial grade ply-wood experimental sample of 8’x4’. The glue

for control sample was made with 80 kg of UF resin along with 8 kg maida and 2 kg GNPC

(ground nut coconut powder). The following experimental conditions were maintained:

Glue spread = 26-27gm per sq ft.

Pressure = 130 kg per sq cm

Curing temperature = 125-130OC

Curing time = 9, 12, 15 and 18 min for experimental samples and 15 min for the control sample

The value of glue shear strengths

(GSS) determined as per IS:1734

(Part

1983

{Determination of Glue Shear Strength (Second Revision) } were observed and given in Table 2

below:

Table 2

Glue Shear Strength Experiment taking UF Resin as Control

Glue Shear Strength

@ kg per sq cm

Sample

Curing Time

Value

No.

9 min

1050

12 min

1200

15min

1450

18 min

1250

Shear strength of the Control Sample with

commercial UF resin with identical conditions and

the curing time of 15 min was determined as

1000 kg per sq cm.

It is evident from the results of Experiment 1 that the performance of the product of this invention is better

than the commercially used UF resin of the prior art under similar working condition. However, necessary

optimization with regard to curing time with new formulation is required; at lower curing time, the shear

strength is below the optimum whereas at higher curing time, the shear strength drops below the optimum.

The use of formalin, however, is not preferable and alternative cross-linking agents are being developed.

Experiment 2

An aqueous solution of the 200 g of denatured guar protein in 400 g water is mixed with 600 g kymene^α

557H and is directly used in making a standard

12 mm thickness commercial grade ply-wood

experimental sample of 1’ x 1’ with experimental conditions used as in Experiment 1.

While the glue shear strength (kg per sq cm) of the control sample was 1000, the same for the test sample

was 1580, far exceeding that of the control sample using UF resin of the prior art.

This clearly demonstrates that the resin obtainable from this invention shows higher binding performance

as compared to the commercially available UF resins.

Experiment 3

In this experiment, while the glue for control sample constituted 90 kg UF resin along with 9 kg maida and

1 kg GNCP, the same for the experimental resin was prepared by using 10 kg of denatured guar protein

with 45 kg of water and 45 kg of UF resin. These were used in making a standard 18 mm thickness of

commercial grade ply-wood experimental sample of 8’x4’. The experimental conditions maintained here

were as follow:

a) Glue spread = 26-27 gm per sq ft

b) Pressure = 130 kg per sq cm.

c) Curing temperature = 125-130OC

d) Curing time = 23 min

The value of glue shear strengths

(GSS) determined as per IS:1734

(Part

1983

{Determination of Glue Shear Strength (Second Revision) } were observed and given in Table 3

below:

…………………………..

^αKymene 557H is commercially available amine-epichlorohydrin type of resin from Hercules Inc. used in this

experiment as a cross-linking agent

Table 3

Glue Shear Strength Experiment taking UF Resin as Control

Glue Shear Strength

@ kg per sq cm

SNo

Resin

Value

UF resin (control)

1100

Experimental resin

1600

It is evident from the results shown above that the binding performance of the adhesive

composition of this invention is significantly better than the commercial product of the prior art

offering the same or more strength of the plywood. The product of this invention is capable of

avoiding the environmentally sinister UF resin altogether or can work with a significantly reduced

amount.

Examples and Mode of Enablement

To validate industrial applicability of the disclosed invention, a number of experiments towards

optimization of operating conditions were carried out. As already described, a number of variants

in different modes play their part at each step which has been tried with the basic understanding

of the role of each constituent to work out the ‘best mode’ of working of this invention. Following

experimental details sum of the ‘best mode of enablement’ as discovered.

Denaturing Process

Denaturing process of guar protein with different agents has considerable impact on the adhesion

property and bonding strength of the glue composition prepared with the denatured guar protein.

The best mode of evaluating the suitability of a denaturant and the reaction conditions can,

therefore, be set up through experimental plywood making process with glue compositions made

with different denatured protein preparations as simulated to industrial scale processes. The

quality of experimental plywood pieces thus prepared can be measured in terms of i) Water

resistance and ii) Glue Shear Strength as per Indian standards IS:1734 (Part-6) and IS:1734

(Part-4)-1983 respectively.

Making of Plywood Samples and Testing

Standard plywood making procedure was employed using the experimental and reference glue

compositions for making a 6mm ply with arrangement of face veneers and core veneers as

shown in Figure 3. While the face veneers are on the outer surface, the core veneers comprising

of poplar and eucalyptus (known commonly as ‘safeda’ in India) alternatively with their strands

transverse to each other as shown in Figure 3.

A pre-determined amount of glue was spread between each surface and the operating conditions

used for all the samples and reference standard ply were identical and conformed to the following

parameters:

a) Glue Spread = 26-27 gm per sq. ft

b) Pressure of the Hot Press = 130 kg per sq. cm

c) Curing Temperature = 125-1300C

d) Curing Time = 8 minutes

The Indian Standard IS:1734 (Part-6) for determination of water resistance is basically an

immersion test, according to which the specimen is kept immersed in warm water at

70±20C

for a period of 3 hours. The test pieces are then removed from warm water and cooled down to

ambient temperature by plunging into water kept at the room temperature. Visual examination

for de-lamination, blister formation etc. is then made for each ply.

The Indian standard IS:1734 (Part-4) in its second revision published in 1983 describes the

method by which glue shear strength (GSS) of the bonding of plywood is determined, according

to which the values of samples along with the reference standard ply were measured and

recorded.

Test Samples of Denatured Guar Protein

In a typical batch for denaturing of guar protein, 100 kg raw guar protein is charged into a

reactor and mixed with a small amount of plasticizer say, glycerol. A suitable denaturant or, a

mixture of denaturants (as described below), in about 10-15 % of the mass of guar protein in an

aqueous medium is slowly added during the course of reaction. The mixture is continuously

heated at 30-950C over a period 1-9 hours. The reaction mass is then cooled to room

temperature and neutralized with ~50% sulphuric acid solution or other inorganic / organic acids.

About 110 kg of the denatured guar protein in a semi-solid state is thus obtained which is then

dried and stored in cool and dry place for further use.

Eight test samples of denatured guar proteins with the above method were prepared for

experimental plywood making process and testing the bonding strength of the resulting glue

compositions. These are given below in Table 4:

Table 4

Denatured Guar

Denaturant & the Manner in which Used

Protein Samples

DGP(C)

Denaturant used is 10 - 15 % caustic solution at the initial stages of the

reaction

DGP(U1)

Denaturant is a combination of 10 - 15 % caustic solution at the initial

stages followed by addition of urea when the reaction has proceeded half

way

DGP(U2)

Denaturant is a combination of 10 - 15 % caustic solution at the initial

stages followed by addition of urea at the end of the reaction time

Denaturant used is a combination of 10 - 15 % caustic solution followed

DGP(S)