TITLE
NOVEL POLY(ESTER-AMIDE) HOT MELT ADHESIVE USING CASTOR OIL
FIELD OF THE INVENTION
The invention describes the synthesis of poly (ester-amide) hot melt adhesive by the reaction of a mixture of diol and diamine with sebacic acid. Diol used in the present invention is castor oil; which has been utilized as a potential replacement of dimer acid (polymeric fatty acid) and a bio-based renewable cheap raw material in the synthesis of poly (ester-amide) hot melt adhesive. Whereas, the diamine used is ethylenediamine.
BACKGROUND OF THE INVENTION
Hot melt adhesives are solid materials at room temperature. This are heated and converted in to molten liquid so as to make them ready for application and joining the substrates. To set up the bond, adhesive applied substrates are cooled to room temperature. [E. M. Yorkgitis, Adhesive Compounds - Encyclopedia of Polymer Science and Technology. John Wiley & Sons Inc., New York (2001) 259] When in the molten state, adhesives must have a relatively low viscosity so as to completely wet the surface of the substrates to be joined. Substrates must be cooled slowly to have sufficient time to completely wet the surface roughness of the substrate. The substrates must be joined immediately on the application of the hot melt adhesive. [E.M. Petrie, Handbook of adhesives and sealants. McGraw Hill Professional, USA (2000) 321] Degree of tackiness of the hot melt adhesive depends on the formulation of the adhesive. Hot melt adhesives cool to harden and do not chemically cross-link, providing an open time of a few seconds to a few minutes [E. M. Yorkgitis, Adhesive Compounds - Encyclopedia of Polymer Science and Technology. John Wiley & Sons Inc., New York (2001) 259]. Hot melt adhesives are usually solid at temperatures below 80 °C; whereas they have a typical application temperature in the range of 150-200 °C [E.M. Petrie, Handbook of adhesives and sealants. McGraw Hill Professional, USA (2000) 321].
Materials generally utilized as hot melt adhesives include:

• ethylene and vinyl acetate copolymers,
• polyvinyl acetates,
• polyethylene,
• amorphous polypropylene,
• block copolymers (styrene butadiene rubber),
• polyamides,
• poly (ester-amide),
• polyesters, etc
Hot melt adhesives can be pre-applied as powder or adhesive spheres, in melt liquid form, as dispersion or as an adhesive foil thus the joining procedure can happen at any time later on [S. Bohm, G. Hemken, E. Stammen and K. Dilger, J.Adhes.Interfac. 7 (2006) 28]. Hot melt adhesives are largely used in the manufacture of shoe assemblies, kitchen and bathroom cabinets, telecommunication cable repair sleeves, and window assembly [C.R. Frihart, IntJ.Adhes.Adhes. 24 (2004) 415].
This invention is concerned with synthesizing poly (ester-amide) polymers, especially poly (ester-amide) hot melt adhesive using a mixture of diol, diacid and diamine. In particular, this invention relates to synthesizing poly (ester-amide) hot melt adhesive using castor oil, sebacic acid and ethylenediamine.
Regardless of wide research and developments in the manufacturing of polymers, there are still certain areas where scope exists for improvement that can consequently prove economically beneficial. For example, using novel bio-based renewable cheap raw material in the synthesis of poly (ester-amide) hot melt adhesive.
Utilizing castor oil as a novel source of diol can be one such approach for reducing the cost of raw materials used in synthesizing poly (ester-amide) hot melt adhesive as well as

a way of utilizing a bio-based raw material in poly (ester-amide) synthesis. India is a leading producer of castor oil (1104.8 kg/ha). Cost of castor oil produced in India is around 0.41 $ per pound. [M. M. Gui, K. T. Lee, S. Bhatia, Energy 33 (2008) 1646]
Pramanik et al. prepared antistatic nanofiber nanocomposite materials using castor oil based hyperbranched poly (ester-amide)/polyaniline. Initial degradation temperature increased, while, the sheet resistance decreased with increased addition of polyaniline in the hyperbranched poly (ester-amide). [S. Pramanik, J. Hazarika, A. Kumar, N. Karak, Ind. Eng. Chem. Res. 52 (2013) 5700] They also investigated the properties of poly (ester-amide) synthesized from N,N-bis(2-hydroxy ethyl) fatty amide of castor oil with maleic anhydride, isophthalic acid and phthalic achydride. [S. Pramanik, K. Sagar, B. K. Konwar, N. Karak, Prog. Org. Chem. 75 (2012) 569] Ickowicz et al. synthesized biodegradable polyesters using castor oil and citric acid, for a potential use as soft tissue augmentation. [D. E. Ickowicz, M. Haim-Zada, R. Abbas, D. Touitou, A. Nyska, L. Golovanevski, C. F. Weiniger, J. Katzhendler, A. J. Domb, Polym. Adv. Technol. 25 (2014) 1323] Sharma et al. investigated the miscibility of poly (ester-amide) derived from linseed oil and dehydrated castor oil with poly (vinyl alcohol). Dehydrated castor oil based poly (ester-amide), when added in the proportion of 80:20 with poly (vinyl alcohol) was able to provide optimized improvement in the toughness and moisture uptake, showing capability to be used as a commercial material. [H. O. Sharma, M. Alam, U. Riaz, S. Ahmad, S. M. Ashraf, Int. J. Polym. Mater. Polym. Biomater. 56 (2007) 437] Shende et al. prepared a range of poly (ester-amide)s from dehydrated castor oil, and various dibasic acids like phthalic anhydride, sebacic acid, succinic acid and adipic acid. [P. G. Shende, A. B. Jadhav, S. B. Dabhade, Pigment Resin Technol. 31 (2002) 310] Recently, Kadam et al. explored the utilization of castor oil, in addition to polymeric fatty acid and ethylenediamine, in the synthesis of poly (ester-amide) based hot melt adhesive. [P. Kadam, P. Vaidya, S. Mhaske, Int. J. Adhes. Adhes. 50 (2014) 151]

Detail studies of the prior art shows the utilization of castor oil in the synthesis of poly (ester-amide) polymers. However, no work has been reported on the utilization of combination of castor oil, sebacic acid and ethylenediamine in the synthesis of poly (ester-amide) based hot melt adhesive.
The principle objective of the present invention is to utilize a novel bio-based renewable cheap raw material - castor oil, in the synthesis of poly (ester-amide) hot melt adhesive in addition to ethylenediamine and sebacic acid.
SUMMARY OF THE INVENTION
The present invention comprises a poly (ester-amide) composition with improved strength and adhesion properties, obtained by means of condensation polymerization of substantially equivalent proportions of a mixture of castor oil (bio-based renewable cheap diol), ethylenediamine and sebacic acid. The poly (ester-amide) composition of the present invention are useful as hot melt adhesives.
DETAILED DESCRIPTION OF THE INVENTION
The reactants utilized to synthesize the poly (ester-amide) composition of the present invention are known in the literature, and also the methods of their preparation.
The hot melt adhesive of this invention comprise; the product of polymerization of
a. castor oil,
b. sebacic acid, and
c. ethylenediamine
Chemical composition of castor oil is listed in Table 1. It has a chemical structure consisting of two or three (mostly three) reactive functional groups (hydroxyl). [M. A. Meier, J. O.

Metzger, U. S. Schubert, Chem. Soc. Rev. 36 (2007) 1788] Castor oil is extensively utilized in synthesis of polyurethane and polyester resins. [S. F. Guner, Y. Yagci, A. E. Tuncer, Prog. Polym.Sci. 31 (2006)633]
Table 1
Sr. No. Acid Name Percentage (%)
1. Ricinoleic acid 80-96
2. Oleic acid 2.5 - 7
3. Linoleic acid 0.5 - 4.5
4. a- Linoleic acid 0.4 - 1
5. Stearic acid 0.3 - 0.9
6. Palmitic acid 0.4-0.9
7. Dihydroxystearic acid 0.2 - 0.4
8. Other 0.2-0.4
The diamine utilized in the present study was ethylenediamine; however, other
diamines can also be utilized. The diamines can be one or more of the known aliphatic,
aromatic or cycloaliphatic diamines consisting of 2 to 20 carbon atoms in their molecular
structure. Other preferred diamines can be 1,3-diaminopropane, 1,4-diaminobutane,
terephthalyl diamine, known as p-xylene diamine, 1,6-hexamethylene diamine, 4,4'-
methylenebis(cyclohexylamine), 2,2di-(4-cyclohexylamine)propane, polyglycol diamines,
isophorone diamine, isophthalyl diamine, known as m-xylene diamine,
cyclohexanebis(methylamines), bis-l,4-(2'-aminoethyl)benzene and 4,4'
methylenebis(cyclohexylamine); which are commercially available and prepared by well known methods.

The diacid used in the present study was sebacic acid; however, other diacids can also be utilized. These diacids include aliphatic, cycloaliphatic and aromatic diacids. Representative of such diacids, which can contain from 2 to 20 carbon atoms, are oxalic, glutaric, malonic, adipic, succinic, suberic, azelaic, sebacic, dodecanoic and pimelic acid. Methods of preparing these diacids are well-known, and they are also available commercially. It should be understood that use of the corresponding acid anhydrides, esters and acid chlorides of this acids is included in the term "diacids".
Preferred compositions of diamine are from about 10 to 95 equivalent percent; whereas, the preferred composition of diol are from 5 to 80 equivalent percent.
The methodology and common method of polymerization of the mixed reactants are generally familiar. Kindly refer to the U.S. Pat. Nos. 4,611,051 and 3,377,303 for detailed information. In order to obtain high molecular weight polymer with molecular uniformity, the ratio of total acid equivalent present in sebacic acid to total amine equivalents present in ethylenediamine and hydroxyl equivalents present in castor oil was kept at, approximately, 1. Slight excess of acid or amine and alcohol are acceptable, however, this ratio is preferred to be maintained between 0.9:1 and 1:1.1.
The four necked 500 ml flask was equipped with stirring system (moon shaped teflon blade stirrer attached to stirring motor), condenser (double walled with water as coolant. Flow rate of water was maintained at 1 1/min), nitrogen gas inlet (flow rate of nitrogen was maintained at 500 ml/min) and temperature controller. To the flask was added castor oil, ethylenediamine and sebacic acid. Order of addition of reactants is: castor oil, ethylenediamine and sebacic acid. Reactants are heated to a temperature from about 120 to 170 °C, to initiate polymerization. Thereafter, the temperature is increased so as to sufficiently distill off the water of condensation. Condensation polymerization occurs at a

temperature from about 60 °C to about 300 °C, preferably in the range of 150 °C to 270 °C. Preferably inert gas atmosphere such as nitrogen gas atmosphere is utilized to carry out heating. Polymerization catalyst (p-toluene sulphonic acid, cone, sulphuric acid, phosphoric acid, tin oxalate etc.) may be used in catalytic proportion. Catalyst can be added either to the initial reaction mixture or just earlier to when polymerization rate decreases. Concentration of catalyst in the reaction system is preferred to be in the range of 0.001 to 3 wt%; and most preferably 0.01 wt% of the total mass.
Reaction mixture is heated until the acid value and amine value of the reaction mass decreases below 10 mg KOH/g sample, and preferably below 5 mg KOH/g sample. Aliphatic linear monoacids like stearic acid, palmitic acid or phenyl benzoate may be added to the reaction mixture to control the molecular weight of the reacting mixture and also its acid and amine value.
Present invention may be carried out at atmospheric pressure or at a slightly higher pressure. However, it is advantageous to operate under vacuum, towards the end of the polymerization so as to remove any by-products, water of condensation and unreacted diamine, which ultimately helps in driving the polymerization reaction towards completion. Time for polymerization is about 2 to 25 hours; depending on the nature of the reactants used in polymerization. Any conventional convenient reactor vessel may be used to condense the reactants and carry out polymerization.
The following examples serve to illustrate the spirit and scope of the invention, which are set forth for purposes of illustration only and are not to be construed as limiting the scope of the invention in any manner. Glass transition temperature (Tg, °C), melting temperature (Tm, °C) and crystallization temperature (Tc, °C) of the synthesized poly (ester-amide) hot melt adhesive was determined using a differential scanning calorimeter (Q100 DSC, TA

Instruments), wherein the scanning rate was maintained at 10 °C/min. Tensile strength (MPa) and elongation at break (%) of the adhesive was determined as per the ASTM standard of D-638. Shore D hardness was evaluated as per ASTM D2240. Adhesion strength like T-peel strength (N/mm) and lap shear strength (MPa) were determined in accordance with the ASTM standards of D1876 and D1002-72 respectively.
EXAMPLES 1 and 2
These examples are not examples of the present invention, but are presented for comparative purposes.
EXAMPLE 1
A polymer was prepared with the following reactant composition:
Sr. No. Acid Name Equivalent %
1. Polymeric fatty acid* 50.0
2. Ethylenediamine 45.0
3. Castor oil 5.0
* Union Camp Corporation, Wayne, New Jersey,
Unidyme ® 18 having the composition:
Monomer 0.5 wt%
Dimer 98 wt%
Trimer 1.5 wt%
Reactants were all charged in a reaction vessel and refluxed at a temperature of 125 - 155 °C, under a blanket of nitrogen gas for 3 h, with continuous stirring at 1500 rpm. The mixture was then heated gradually from the reflux temperature to 210 °C, during which water was removed by distillation. 0.1 wt% p-toluene sulphonic acid was added and the mixture was heated at temperatures of 200 to 230 °C under a vacuum of 0.05 - 5 mm Hg. After 6 h, the acid and amine values of the polymer was determine to be 13.7 and 14.0 mg KOH/g sample,

respectively, and the melt was stirred under vacuum for an additional 1 h. The synthesized polymer was then poured on Teflon tray and allowed to cool. Obtained properties are listed in Table 3.
EXAMPLE 2
The procedure of Example 1, was repeated except that the proportions of the reactants were changed. The proportions are mentioned in Table 2; whereas, the properties are listed in Table 3.
EXAMPLES 3-5
The procedure of Example 1 was repeated except that sebacic acid was used to replace polymer fatty acid and/or the proportions of the reactants was changed. The proportions and reactants are mentioned in Table 2; whereas the determined properties are listed in Table 3.
Table 2
Reactant Example 2 Example 3 Example 4 Example 5
(equivalent %) (equivalent %) (equivalent %) (equivalent %)
Polymeric fatty acid 50.0 -
Sebacic acid - 50.0 50.0 50.0
Ethylenediamine 35.0 45.0 40.0 35.0
Castor oil 15.0 5.0 10.0 15.0

TABLE 2

Properties Example No.
1. 2. 3. 4. 5.
Acid Value (mg KOH/g sample) 9.8 9.9 9.2 9.4 9.5
Amine Value (mg KOH/g sample) 5.2 4.7 5.5 5.1 5.3
Tg(°C) 0.0 -9.3 27.4 11.2 -18.3
Tm(°C) 90.0 76.0 247.8 225.9 211.1
Tc (°C) 82.0 59.0 227.8 197.5 161.0
Tensile Strength (MPa) 8.7 2.8 9.7 8.3 7.4
Elongation at Break (%) 24.8 52.7 30.2 36.8 42.9
Shore D Hardness 57 42 65 58 51
T-Peel Strength (N/mm) 2.2 1.9 2.7 2.5 2.2
Lap Shear Strength (MPa) 3.9 1.8 3.6 3.9 4.3
While the invention has been described in connection with preferred embodiments, it is not intended to limit the invention to the particular forms set forth, but on the contrary, it is intended to cover such alternatives, modifications, equivalents as many are included within the spirit and scope of the invention.
We Claim:
1. A poly (ester-amide) hot melt adhesive composition which comprises the product of polymerization of:

a. from about 10 to 95 equivalent percent diamine; whereas, the preferred
composition of diol are from 5 to 80 equivalent percent,
b. a substantially equivalent amount of from 20 - 85 equivalent percent of the
organic diacid
2. The poly (ester-amide) adhesive composition of claim 1, wherein the organic diamine
is selected from the group consisting of ethylenediamine, 1,3-diaminopropane, 1,4-
diaminobutane, terephthalyl diamine, known as p-xylene diamine, 1,6-hexamethylene
diamine, 4,4'-methylenebis(cyclohexylamine), 2,2-di-(4-cyclohexylamine)propane,
polyglycol diamines, isophorone diamine, isophthalyl diamine, known as m-xylene
diamine, cyclohexanebis(methylamines), bis-l,4-(2'-aminoethyl)benzene and 4,4' -
methylenebis(cyclohexylamine).
3. The poly (ester-amide) adhesive composition of claim 1, wherein the organic diacid is
selected from the group consisting of oxalic, glutaric, malonic, adipic, succinic,
suberic, azelaic, sebacic, dodecanoic and pimelic acid.
4. The poly (ester-amide) adhesive compositions as defined in claim 1 have application
as hot melt adhesives.