Hydroxy Ethyl Fatty Amide Effect on the Perfomance ..Acrylic Copolymers

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One of the major pollutants emittedby a surface coating is organic solvent used during processing andapplication. Hence, efforts have been made to develop alternativetechnologies that minimize the use of organic solvents in surfacecoatings. These include the use of coating curing agents derived fromvegetable oils, which have been directly used to obtain coating films.Since these oils, by themselves, cannot directly meet the desired filmproperties, a number of oil modifications have been proposed such asalkyd, epoxy, polyesteramide, polyurethanes, polyurethaneamide, etc.The polyesteramide resins hold considerable application scope in thecoatings field. A number of polyesteramides have been developed fromdifferent oils e.g., dehydrated castor oil, pilu fat, argemone,linseed, etc. The presence of repeating units of ester (-COOR) andamide (-NCOR) in the polymeric chain of polyesteramide (PEA) improvesthe ease of application, thermal stability, chemical and waterresistance, and causes faster drying and enhanced hardness over normalalkyds. These polyesteramides have shorter curing times at elevatedtemperature, while considerably longer times at room temperature.
                                                

Copolymer Code	Monomer(mol)	Number Average Molecular                   weight(Mn)	Weight Average Molecular                   weight (Mw)	Poly Dispersity Index                   (PDI)	Acid Value
A	1	1	8297	19210	345

In the present study, an acid-functional acrylic copolymer has beensynthesized using butyl methacrylate and maleic anhydride. In addition,the hydroxyl ethyl fatty amide of castor oil has also been synthesizedand used as a curing agent for the acid-functional acrylic copolymer toform polyesteramide resins. The effect of crosslinking agent on theacrylic copolymers was examined. A series of coating compositions withvarying amounts of acrylic copolymer and hydroxyl ethyl fatty amidewere prepared, and their mechanical, optical and chemical resistanceproperties studied.
Experimental        
       Reagents
      Castor oil was procured from a commercial manufacturer. Maleicanhydride, butyl methacrylate (BMA), diethanolamine, zinc oxide,methanol, xylene, acetone, and potassium hydroxide were of LR grade.

Synthesis of Acrylic Copolymer         
                               The copolymer was synthesized by dissolving maleic anhydride (1 mol) in 100 ml of xylene in a 3-neck flask with inlet for N2gas, reflux condenser and mechanical stirrer. BMA (exactly 1 mol)containing 1.4 gm of benzoyl peroxide was added drop wise at a constantrate into the flask over the period of 2 hours keeping the temperatureconstant at 95 °C. The reaction mass was stirred for another 2 hours tocomplete the reaction. The resulting copolymer was diluted with acetoneand precipitated with methanol with constant stirring. Table 1 showsthe characteristics of the acrylic copolymer.
Synthesis of Hydroxyethyl Fatty Amide (HEFA)
      The oil (0.1 mol) was placed in a multi-necked flask equipped withstirrer, thermometer and condenser, and heated to 150 °C with thediethanolamine (0.34) and zinc oxide (0.002). The temperature wasraised to 200 °C and maintained at ± 200 °C until it gave a methanolsolubility test. Samples were periodically withdrawn and mixed with twovolumes of methanol at room temperature; the disappearance of turbidityshowed the completion of the reaction. The formation of hydroxy ethylfatty amide was further confirmed by a TLC method. After reactioncompletion the product was dissolved in diethyl ether, washed with 15%NaCl solution and dried over anhydrous sodium sulphate. The etherealsolution was filtered and evaporated in a vacuum evaporator to obtainthe light-colored hyroxy ethyl fatty amide of dehydrated castor oil.Table 2 shows the physico-chemical properties of hydroxyl ethyl fattyamide of castor oil.
          

[tr=#f4f8ff][/tr]                    Properties                    Hydroxyethyl Fatty Amide (HEFA)                                        Acid value                    4.00                    Iodine value                    80.00                    Viscosity at 25 °C                    5.00                    Specific gravity                    0.95                    Refractive Index                    1.4770              Table 2: Properties of hydroxyl ethyl fatty amide (HEFA)

Measurements      
      Infraredspectra of the synthesized co-polymer were recorded using aPerkin-Elmer 1750 FT-IR spectrophotometer. Molecular weight wasdetermined by GPC (model HPLC 600, RI detector with two ultra styragelcolumns); polystyrene was used as a standard, and THF as eluent. ForDSC analysis, a universal V4.2E TA instruments Q20 differentialscanning calorimeter was used. The temperature range was kept as 20-200°C at the rate of 20 °C/min. The analysis was carried out in an argonatmosphere at the rate of 40 ml/min. The thermal stability of the resinwas measured by using a universal V4.2E TA instruments Q50thermogravimetric analyzer under dynamic scans from 0-600 °C at therate of 20 °C/min under nitrogen flow at the rate of 30 ml/min.Viscosity of the fatty amide was determined by Brookfield cone andplate 2000 + viscometer, at 25 °C.
Coating Sample Preparation
                Coatingcompositions with varying ratios of acrylic copolymer and HEFA wereprepared using xylene/acetone (95/5% v/v) as a solvent. All thecompositions were thinned with the above mixture to 50% weight ofnonvolatile matter. The sample designations are given in Table 3.Coating films were prepared by applying the various coatingformulations on mild steel panels using a bar applicator. Film drythickness was maintained at 40 ± 5 microns and cured for the evaluationof various mechanical and chemical resistance properties.
          

Sample Code                    EOPA                    HDDA                    TMPTA                    PE-1                    A                    HEFA                    1:0.3                    PE-2                    A                    HEFA                    1:0.5                    PE-3                    A                    HEFA                    1:0.7                    PE-4                    A                    HEFA                    1:1              Table 3: Formulation of             coating samples

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Results and Discussion

Spectral Analysis of BMA-MA Copolymer
[IR spectrum of acrylic copolymer]
Figure 1: IR spectrum of acrylic copolymer

The IR spectrum of BMA-MA copolymer, shown in Figure 1, shows the presence of an absorption band at 2972 cm-1 due to carboxylic acid of the saturated anhydride. This confirms the inclusion of maleic anhydride in the copolymer. A strong band at 1716 cm-1 may be due to the ester group of the butyl methacrylate.

Spectral Analysis of Hydroxyethyl Fatty Amide (HEFA)
[IR spectrum of HEFA]
Figure 2: IR spectrum of HEFA

Figure 2 shows the IR spectrum of HEFA. A strong absorption at 720 cm-1 and a weak band at 920 cm-1 can be attributed to (-C-H-) bending arising from poly-methylene groups (-CH2-) groups and (-CH=CH-) groups, respectively, which are present in the fatty amide. A very strong absorption band at 1050 cm-1 is thought to be arising out of (-C-O-) stretching and bending of the primary alcohol. A strong absorption band at 1460 cm-1 can be attributed to (-C-H-) bending and to the presence of tertiary amide. A strong absorption band at 3350-3400 cm-1 may be due to the free (-OH) group.

Molecular Weight
[Molecular Weight of acrylic copolymer]
Figure 3:Molecular Weight of acrylic copolymer

Gel permeation chromatograms are shown in Figure 3. Mn was found to be 8297 and Mw of the resin was found to be 19210.

Thermal Analysis
[TGA thermogram of polyesteramide]
Figure 4: TGA thermogram of polyesteramide

Figure 4 shows the TGA thermogram of the polyesteramide resin. It is quite obvious that the thermal stability of the resin is quite high as only 10% weight loss is observed up to a temperature of 250 °C. Beyond this temperature a sluggish decomposition takes place and, as a result, about 50% weight loss occurs up to 370 °C and 80% weight loss occurs up to 405 °C.
[DSC of polyesteramide]
Figure 5: DSC of polyesteramide

In Figure 5 an endothermic peak is observed at 155 °C in the DSC thermogram of the resin. The TGA thermogram does not show any significant weight loss at this temperature. The endothermic peak can be attributed to the melting of the resin.


Coating Film Characterization

The various coating formulation panels were cured and tested for different mechanical and chemical resistance properties, as per test methods viz. gloss at 60° (ASTM D 523-99); scratch hardness (ASTM D 5178); pencil hardness (ASTM D 3363-00); and chemical resistance (EN: 438-2:1991). The results are given in Table 4.
Property
       
PE-1
       
PE-2
       
PE-3
       
PE-4
Scratch hardness
       
3200
       
2700
       
2500
       
2400
Pencil hardness
       
5H
       
4H
       
3H
       
2H
Cross hatch adhesion (%)
       
100%
       
100%
       
100%
       
100%
Flexibility
       
Pass
       
Pass
       
Pass
       
Pass
Impact resistance
       
125
       
140
       
150
       
165
Gloss
       
86.5
       
87.4
       
89.3
       
90.2
Table 4: Coating films physical properties

Scratch Hardness

Scratch hardness results are shown in Table 4. The comparison of mechanical properties of the films of various compositions reveals that, in general, scratch hardness increases as the amount of curing agent (HEFA) decreases. The scratch hardness property of the film, in general, improves with an increase in the film complexity resulting from a higher degree of crosslink density. The amount of HEFA has a controlling effect in the scratch hardness of all the coating films. The scratch hardness of coating films decreases as the HEFA content increases. This might be due to the presence of a nonpolar fatty acid moiety in HEFA which brings a plasticizing effect to the films.

Cross Hatch Hardness

Cross hatch was measured by using a cross cut adhesion tester. The test was rated good if 5% of squares were removed. All the coating films showed good cross hatch hardness properties because a significant degree of crosslinking has taken place in the coating films.

Gloss

Gloss was measured using a Triglossometer (Sheen). All the coating films had good gloss.

Flexibility

Flexibility was carried out on 1/4 inch Mandrel bend tester. Films of all the coatings compositions were flexible enough to pass (Table 4).

Impact Resistance

Impact resistance was measured using an impact tester. The comparison of impact resistance of the films reveals that, in general, coating films having lower HEFA content have poorer impact resistance, indicating the plasticizing effect of the crosslinking agent in the coating films. The presence of the nonpolar fatty acid moiety of the HEFA is thought to improve the film toughness resulting in the high impact resistance.
Chemical Resistance Properties
Chemical
       
PE-1
       
PE-2
       
PE-3
       
PE-4
1.0 N H2SO4
       
A
       
A
       
A
       
A
1.0 N NaOH
       
B
       
B
       
B
       
A
Distilled water
       
A
       
A
       
A
       
A
MTO
       
A
       
A
       
A
       
A
Methyl Ethyl Ketone
       
B
       
B
       
B
       
A
Xylene
       
A
       
A
       
A
       
A
Ethyl alcohol
       
C
       
C
       
C
       
B
Table 5: Chemical Resistance Properties
Conclusion

Acrylic copolymer was synthesized successfully using butyl methacrylate and maleic anhydride. Hydroxy ethyl fatty amide derived from castor oil was also synthesized and used as a crosslinking agent for these acrylic copolymer/resins to get polyesteramide resins. The study shows that the mechanical and chemical resistance properties of the films are dependant on the HEFA content of the compositions; an optimum acrylic copolymer and HEFA i.e., PE-4 ratio, can be selected to obtain the balanced film properties.