DESC:FIELD
The present disclosure relates to an adhesive composition.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which it is used indicates otherwise.
Tensile strength: Tensile strength refers to a measurement of the force that can be applied to a material before it yields (stretches irreparably) or breaks.
Flexural strength: Flexural strength of a material is defined as its ability to resist deformation under load. Flexural strength indicates how much force is required to break a test sample of defined diameter.
Compressive strength: Compressive strength refers to the maximum stress a material can sustain under crush loading.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Adhesives are used in many applications such as packaging, construction, automobile, electronics, and the line. An adhesive formulation/composition depends on the base materials and requirements of a particular application. Wood has been used as an important building material. Over the time, different types of artificial wood composites such as thermoset and thermoplastic composites are used in the structural applications.
However, these composites are prone to deformations while exposed to more stringent environmental conditions like higher temperatures, direct sunlight, and humidity. Typically, the composites at thinner sections as well as sections under stress are more prone to deformations.
Conventionally, composites impregnated or filled with inorganic fillers or ground fillers are used for structural applications. Though thermoset composites impregnated with fillers are quite stable in dimension, these composites often undergo thermal deformation with heat and humidity, leading to its commercial value destruction.
There is, therefore, felt a need to develop an alternative to improve the thermal stability of the wood composites.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide an adhesive composition that enhances thermal stability, flexural strength, and flexural modulus of the wood composites and avoid shrinkage of the wood composites.
Another object of the present disclosure is to provide an adhesive composition that can be used with different substrates.
Yet another object of the present disclosure is to provide a process for the preparation of the adhesive composition.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure relates to an adhesive composition and a process for its preparation. In an aspect, the coating composition comprises a first component comprising (i) an epoxy resin in an amount in the range of 30 to 70 wt% by the total weight of the first component; (ii) at least one diluent in an amount in the range of 5 to 10 wt% to the total weight of the first component; (iii) glass fiber reinforced polymer in an amount in the range of 30 to 60 wt% to the total weight of the first component; and a second component comprising (i) curing agent in an amount in the range of 20 to 60wt% by the total weight of the second component; and (ii) glass fiber reinforced polymer in an amount in the range of 40 to 60 wt% the total weight of the second component; wherein the first component and the second component are mixed in a weight ratio in the range of 10:5 to 10:7 before application to obtain said adhesive composition.
In another aspect, the process for the preparation of adhesive composition comprises blending of at least one epoxy resin with at least one diluent at a speed in the range of 200 rpm to 300 rpm for a first predetermined time period to obtain a resin mixture. Further, a glass fiber reinforced polymer is blended with the resin mixture at a speed in the range of 300 rpm to 400 rpm for a second predetermined time period to obtain the first component. Separately, blending at least one curing agent and a glass fiber reinforced polymer at a speed in the range of 300 rpm to 400 rpm for a third predetermined time period to obtain the second component. The first component and second component are mixed before application to obtain the adhesive composition. The adhesive composition of the present disclosure provides enhanced flexural strength, tensile strength, and compressive strength to substrates.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1. illustrates the graph depicting a tensile strength of the adhesive cast sheet of the present disclosure;
Figure 2. illustrates the graph depicting a flexural strength of the adhesive cast sheet of the present disclosure;
Figure 3. illustrates the graph depicting a compressive strength of the adhesive cast sheet of the present disclosure; and
Figure 4. illustrates the graph depicting a flexural strength of the adhesive composition of the present disclosure and other adhesive systems on the wood substrate.
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details, are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
Wood and or artificial wood composites are prone to deformations while exposed to more stringent environmental conditions like higher temperatures, direct sunlight, and humidity. Conventionally, composites impregnated or filled with inorganic fillers or ground fillers were used for structural applications. Despite being stable in dimension, these composites often undergo thermal deformation with heat and humidity. Various adhesives have been also used in an effort to improve the thermal stability of the wood composites. However, there is still a need to improve the thermal stability and avoid shrinkage of the wood composites upon exposure to stringent environmental conditions, which results in destruction of the commercial value of the composite.
The present disclosure provides an economical adhesive composition, which improves thermal stability and avoids shrinkage of the wood composites.
In an aspect of the present disclosure, there is provided a two-component adhesive composition.
The coating composition comprises a first component comprising (i) an epoxy resin in an amount in the range of 30 to 70 wt% by the total weight of the first component; (ii) at least one diluent in an amount in the range of 5 to 10 wt% to the total weight of the first component; (iii) glass fiber reinforced polymer in an amount in the range of 30 to 60 wt% to the total weight of the first component; and a second component comprising (i) curing agent in an amount in the range of 20 to 60 wt% by the total weight of the second component; and (ii) glass fiber reinforced polymer in an amount in the range of 40 to 60 wt% by the total weight of the second component. In an embodiment, the first component and second component are mixed in a weight ratio in the range of 10:5 to 10:7 before application to obtain said adhesive composition.
In an embodiment, the epoxy resin is at least one selected from bisphenol-A based epoxy resin, bisphenol-F based epoxy resin, modified bisphenol based epoxy resin, and hydrogenated bisphenol based epoxy resin. In an exemplary embodiment of the present disclosure, the epoxy resin is bisphenol-A based epoxy resin.
In an embodiment, the diluent is at least one selected from phenyl glycidyl ether, butanediol diglycidyl ether, and cardanol glycidyl ether. In an exemplary embodiment of the present disclosure, the diluent is 1,4 - butanediol diglycidyl ether.
In an embodiment, the polymer is selected from epoxy polymer, polyester, and vinyl ester polymer. In an exemplary embodiment of the present disclosure, the polymer is polyester.
In an embodiment, the particle size of the glass fiber reinforced polymer is in the range of 300 to 400 microns. The ‘glass fiber reinforced polymer’ is also referred to as ‘FRP regrind’ or ‘FRP dust’ which is prepared by grinding the composite (unsaturated polyester resin and glass fiber) into powder form. In an exemplary embodiment of the present disclosure, the particle size of the glass fiber reinforced polymer is 350 microns.
In an embodiment, the curing agent is at least one selected from cycloaliphatic amine adducts, aliphatic amine adducts, polyaminoamides, and phenalkamine. In an exemplary embodiment of the present disclosure, the curing agent is cycloaliphatic polyamine.
In another aspect of the present disclosure, there is provided a process for the preparation of the adhesive composition. Particularly, the present disclosure provides a process for the preparation of epoxy resin based adhesive composition.
The process is described in detail.
In a first step, epoxy resin is blended with diluent at a speed in the range of 200 rpm to 300 rpm for a first predetermined time period to obtain a resin mixture. In an exemplary embodiment of the present disclosure, the epoxy resin is blended with diluent at a speed of 250 rpm.
In an embodiment, the epoxy resin is at least one selected from bisphenol-A based epoxy resin, bisphenol-F based epoxy resin, modified bisphenol based epoxy resin, and hydrogenated bisphenol based epoxy resin. In an exemplary embodiment of the present disclosure, the epoxy resin is bisphenol-A based epoxy resin.
In an embodiment, the diluent is at least one selected from phenyl glycidyl ether, butanediol diglycidyl ether, and cardanol glycidyl ether. In an exemplary embodiment of the present disclosure, the diluent is 1,4 - butanediol diglycidyl ether.
In an embodiment, the first predetermined time period is in the range of 5 min to 30 min. In an exemplary embodiment of the present disclosure, the first predetermined time period is 15 min.
In an embodiment, the polymer is selected from epoxy polymer, polyester, and vinyl ester polymer. In an exemplary embodiment of the present disclosure, the polymer is polyester.
In a second step, glass fiber reinforced polymer is blended with the resin mixture at a speed in the range of 300 rpm to 400 rpm for a second predetermined time period to obtain the first component. In an exemplary embodiment of the present disclosure, the glass fiber reinforced polymer is blended with the resin mixture at a speed of 350 rpm.
In an embodiment, the particle size of the glass fiber reinforced polymer is in the range of 300 to 400 microns. In an exemplary embodiment of the present disclosure, the particle size of the glass fiber reinforced polymer is 350 microns.
In an embodiment, the second predetermined time period is in the range of 30 min to 90 min. In an exemplary embodiment of the present disclosure, the second predetermined time period is 30 minutes.
Separately, a curing agent is blended with a glass fiber reinforced polymer at a speed in the range of 300 rpm to 400 rpm for a third predetermined time period to obtain the second component. In an exemplary embodiment of the present disclosure, the curing agent is blended with a glass fiber reinforced polymer at a speed of 350 rpm.
In an embodiment, the curing agent is at least one selected from cycloaliphatic amine adducts, aliphatic amine adducts, polyaminoamides, and phenalkamine. In an exemplary embodiment of the present disclosure, the curing agent is cycloaliphatic polyamine.
In an embodiment, the third predetermined time period is in the range of 30 min to 90 min. In an exemplary embodiment of the present disclosure, the third predetermined time period is 30 minutes.
In an embodiment, the mixture is evaluated for its consistency after the completion of the second predetermined time period and third predetermined time period. On evaluation, if the mixture is not consistent, the mixing process is continued until the uniform consistency of the mixture is achieved.
The so obtained first component and the second component are mixed to obtain the adhesive composition.
In an embodiment, the adhesive composition of the present disclosure is prepared as adhesive cast sheets.
In an embodiment, the adhesive cast sheets are prepared by mixing the first component and second component in a weight ratio of 100:65 to obtain the adhesive composition. The so obtained adhesive composition is poured in the mould to obtain adhesive cast sheets.
The present disclosure provides the economical adhesive composition, which on application enhances thermal stability and avoids shrinkage of the wood composites, even after exposure to stringent environmental conditions for longer durations. The adhesive composition also helps in enhancing the flexural strength, tensile strength, compressive strength, and modulus of the wood composites. The adhesive composition of the present disclosure can be used with a variety of substrates such as wood, artificial wood, metal, plastic, and fiber reinforced polymer (FRP) composite.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
EXPERIMENTAL DETAILS
EXAMPLE 1: Process for the preparation of adhesive composition in accordance with the present disclosure
a) First component
45 gm of epoxy resin (YD 128 resin liquid epoxy resin with medium viscosity produced from bisphenol-A and epichlorohydrin) was charged to the reactor and 6 gm of 1,4 - Butanediol diglycidyl ether (RD 103LE) was added to the resin. The resin and 1,4 - Butanediol diglycidyl ether were blended at a speed of 250 rpm for 15 min to obtain a resin mixture. To the resin mixture, 49 gm of glass fiber reinforced polymer (particle size of 350 microns) was added slowly to the reactor and blended at a speed of 350 rpm for a period of 30 minutes to obtain a first component. The first component was prepared by using the ingredients having the amounts as specified in Table-1.
Table-1
Sr. No. Raw Material gm
1 Epoxy resin (YD 128) 45
2 1,4 - Butanediol diglycidyl ether (RD 103LE) 6
3 Glass fiber reinforced polymer 49
Total 100

b) Second component
Separately, 44.44 gm of cycloaliphatic polyamine (TH 7301) was charged into a separate reactor and 55.56 gm of glass fiber reinforced polymer (particle size of 350 microns) was slowly added to the reactor. The cycloaliphatic polyamine and glass fiber reinforced polymer was blended at a speed of 350 rpm for a period of 30 minutes to obtain a second component. The second component was prepared by using the ingredients having the amounts as specified in Table-2.
Table-2
Sr. No. Raw Material Gm
1 Cycloaliphatic polyamine (TH 7301) 44.44
2 Glass fiber reinforced polymer 55.56
Total 100

The so obtained first component (100 gm) was mixed with the second component (65 gm) using a mechanical mixer for 1 min to 2 min to obtain the adhesive composition.
EXAMPLE 2: Tensile Strength
The tensile strength of the adhesive cast sheet of the present disclosure (3 samples) was determined according to ASTM D638. The samples were evaluated for tensile modulus (Young's modulus), % elongation at break (elongation at yield). The tensile strength was determined according to ASTM D638 using a universal testing machine (UTM) (Instron). The results are provided in table 3 below, illustrated in Figure 1.
Table-3
Sample ID Width
mm Thickness
mm Ultimate Force
KN Ultimate Force
MPa Modulus
GPa Elongation
%
1 13.41 3.90 1.46 27.9 3.47 1.38
2 13.27 3.82 1.39 27.3 3.83 1.23
3 13.31 4.3 1.69 29.5 3.94 1.41
Average 13.33 4.01 1.51 28.2 3.75 1.34

The adhesive cast sheet of the present disclosure has a tensile modulus of > 3.7 GPa, and % elongation at break of > 1.34.
EXAMPLE 3: Flexural Strength
The flexural strength of the adhesive cast sheet of the present disclosure (3 samples) was determined according to ASTM D790. The samples with the dimensions of about 13 mm width and 4 mm depth were placed on two supports and a load was applied at the center. The load at yield provides the flexural strength details. The results are provided in table 4 below, illustrated in Figure 2.

Table-4
Sample ID Width
mm Depth
mm Maximum Force
N Flexural Strength
MPa Modulus
GPa
1 13.05 4.08 112 53 2.42
2 13.01 3.85 88.3 47.3 2.20
3 12.95 4.08 96.5 46.2 1.93
Average 13.00 4.00 98.8 48.8 2.19

The adhesive cast sheet of the present disclosure has a flexural strength of > 48 MPa, and a flexural modulus of > 2 Gpa
EXAMPLE 4: Compressive Strength
The compressive strength of the adhesive cast sheet of the present disclosure (2 samples) was determined according to ASTM D695. The samples were evaluated for compressive strength and modulus using a universal testing machine (UTM) (Instron). The results are provided in table 5 below, illustrated in Figure 3.
Table-5
Sample ID Thickness
mm Width
mm Maximum Force
N Compressive Strength
MPa Modulus
GPa
1 4.21 12.71 3.01 56.3 3.66
2 4.29 13.03 2.88 51.6 3.27
Average 4.25 12.87 2.95 53.9 3.46

The adhesive cast sheet of the adhesive composition of the present disclosure has a compressive strength of > 56 MPa, and a modulus of > 3.5 Gpa.
COMPARATIVE EXAMPLE:
STUDY OF ADHESIVE COMPOSITION:
The adhesive composition of the present disclosure was evaluated for flexural strength by joining the wood substrates.
The first and second component of the adhesive composition in the ratio of 100:65 by weight was mixed by mechanical mixer for 2 min to obtain the adhesive composition. The adhesive composition was applied on a clean wood substrate (RelWood) with a moisture content of not more than 4%. A thin layer of the adhesive composition was applied with the help of a trowel on both surfaces to be stuck. Appropriate support is provided to the joined surfaces by placing weights, or by using a screw or fastener. The excess adhesive composition ooze out from the substrates was wiped with the help of a trowel. The joined substrates are allowed to dry at room temperature overnight before testing.
EXAMPLE 5:
The adhesive composition was evaluated for the flexural strength and deformations of the wood substrates while exposed to the hot conditions. The wood substrates were stuck by 4 different adhesive compositions, i.e. adhesive A (adhesive composition of the present disclosure), adhesive B (glass fiber reinforced polymer + PVC solvent cement), adhesive C (Glass mat + Liquid epoxy system (Epoxy resin (YD 128 – Aditya Birla) and Hardener (TH 7301 – Aditya Birla)), adhesive D (only solvent cement). These substrates were placed in a hot oven at 50 °C for a time period of 6 hrs to 10 hrs. Following the heat treatment, the flexural strength was evaluated by the method discussed above.
The results are provided in table 6 below, illustrated in Figure 4.
Table-6
Sample ID Width
mm Depth
mm Maximum Force
N Flexural Strength
MPa Deflection @ Max Load
mm Modulus
MPa
Sample A1 12.74 17.33 220 19.8 15.6 1000
Sample A2 12.17 17.2 213 20.4 14.8 1090
Sample B1 12.69 17.21 167 15.3 11.3 882
Sample B2 12.51 17.12 177 16.6 11.0 954
Sample C1 12.78 17.54 225 19.7 17.0 917
Sample C2 12.62 17.34 203 18.5 18.1 872
Sample D 13.11 16.69 177 16.3 20.4 712
Average 12.66 17.23 197 18.1

It is observed that adhesive A and adhesive C has shown better flexural strength compared to adhesive B and D. The wood substrates stuck with adhesive D has shown higher deformation.
TECHNICAL ADVANCES AND ECONOMIC SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of an adhesive composition, which
• enhances thermal stability, flexural strength, and modulus of the composites;
• avoids shrinkage and thermal deformation of the composites; and
• is economical.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

,CLAIMS:WE CLAIM:
1. An adhesive composition comprising:
a. a first component comprising
i. epoxy resin in an amount in the range of 30 to 70 wt% by the total weight of the first component;
ii. at least one diluent in an amount in the range of 5 to 10 wt% to the total weight of the first component;
iii. glass fiber reinforced polymer in an amount in the range of 30 to 60 wt% to the total weight of the first component; and
b. a second component comprising
i. curing agent in an amount in the range of 20 to 60wt% by the total weight of the second component; and
ii. glass fiber reinforced polymer in an amount in the range of 40 to 60 wt% the total weight of the second component;
wherein said first component and said second component are mixed in a weight ratio in the range of 10:5 to 10:7 before application to obtain said adhesive composition.
2. The composition as claimed in claim 1, wherein said epoxy resin is at least one selected from the group consisting of bisphenol-A based epoxy resin, bisphenol-F based epoxy resin, modified bisphenol based epoxy resin, and hydrogenated bisphenol based epoxy resin.
3. The composition as claimed in claim 1, wherein said diluent is at least one selected from the group consisting of phenyl glycidyl ether, butanediol diglycidyl ether, and cardanol glycidyl ether.
4. The composition as claimed in claim 1, wherein said polymer is at least one selected from the group consisting of epoxy polymer, polyester, and vinyl ester polymer.
5. The composition as claimed in claim 1, wherein said curing agent is at least one selected from the group consisting of cycloaliphatic amine adducts, aliphatic amine adducts, polyaminoamides, and phenalkamine.
6. The composition as claimed in claim 1, wherein said adhesive composition is suitable to stick substrates selected from wood, wood composite, plastic, metal and fiber reinforced polymer (FRP) composite.
7. A process for the preparation of the adhesive composition as claimed in claim 1, said process comprising the following steps
a. blending epoxy resin and diluent at a speed in the range of 200 rpm to 300 rpm for a first predetermined time period to obtain a resin mixture;
b. blending a glass fiber reinforced polymer to said resin mixture at a speed in the range of 300 rpm to 400 rpm for a second predetermined time period to obtain the first component;
c. separately blending a curing agent and a glass fiber reinforced polymer at a speed in the range of 300 rpm to 400 rpm for a third predetermined time period to obtain the second component; and
d. mixing said first component and said second component before application to obtain said adhesive composition.
8. The process as claimed in claim 7, wherein said first predetermined time period is in the range of 5 min to 30 min.
9. The process as claimed in claim 7, wherein said second predetermined time period and said third predetermined time period are independently is in the range of 30 min to 90 min.

10. The process as claimed in claim 7, wherein the particle size of said glass fiber reinforced polymer is in the range of 300 to 400 microns.
Dated this 5th day of October, 2020

MOHAN RAJKUMAR DEWAN
of R.K. DEWAN & COMPANY
IN/PA-25
APPLICANT’S PATENT ATTORNEY

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI