NOVEL EPOXY NOVOLAC COMPOSITES

Abstract

The present invention disclosed novel epoxy novolac composite comprising environmentally friendly toughening agents based on bio-derived chemicals namely, Difunctional glycidyl ether epoxy resin (Cardolite NC-514) and Polyglycidyl ether of an alkenyl phenol formaldehyde novolac resin (Cardolite NC-547) used for the toughening of epoxy novolac resin namely Poly[(phenyl glycidyl ether)-co-formaldehyde] [PPGEF].

Claims

1. A epoxy novolac composites comprising: a) an epoxy novolac resin; b) hardener for curing epoxy novolac resin; c) polyglycidyl ether of epoxy resin as flexibilizer; characterized in that impact strength of the said composite is in the range of 24 J/m to 69 J/m; wherein polyglycidyl ether of epoxy resin (c) is selected from di-functional glycidyl ether epoxy resin (Cardolite NC-514) and polyglycidyl ether of an alkenyl phenol formaldehyde novolac resin (Cardolite NC-547).

2. The composite as claimed in claim 1, wherein epoxy novolac resin (a) is poly [(phenylglycidyl ether)-co-formaldehyde] (PPGEF).

3. The composite as claimed in claim 1, wherein hardener (b) is selected from the group consisting of 4,4′-diamino-3,3′-dimethyldicyclohexyl methane (BMCHA), diethylene triamine, triethylene tetramine, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, dicyandiamide, methyl hexahydrophthalic anhydride, isophorone diamine, bis(4-aminocyclohexyl)methane, methylenedianiline and meta-phenylenediamine.

4. The composite as claimed in claim 1, wherein tensile strength of said composite is in the range of 63 MPa to 77 MPa.

5. The composite as claimed in claim 1, wherein glass transition temperature (Tg) of said composite is in the range of 90° C. to 120° C.

6. The composite as claimed in claim 1, wherein flexibilizer to resin is in the range of 5 to 30 wt %.

7. The composite as claimed in claim 1, wherein hardener to resin is in the range of 1 to 1.5 equivalents.

8. A process for preparation of epoxy novoloc composite comprising: a. mixing epoxy novolac resin with bio-derived modifier/flexibilizer in amounts ranging from 5 to 30 wt % to obtain mixture; and b. adding hardener to the mixture of step (a) in amounts ranging from 1-1.5 equivalents to obtain the composite.

9. The process as claimed in claim 8, wherein the epoxy novolac resin is poly [(phenylglycidyl ether)-co-formaldehyde] (PPGEF).

10. The process as claimed in claim 8, wherein the natural modifier/flexibilizer is polyglycidyl ether of epoxy resin which is selected from -di-functional glycidyl ether epoxy resin (Cardolite NC-514) and polyglycidyl ether of an alkenyl phenol formaldehyde novolac resin (Cardolite NC-547).

11. The process as claimed in claim 8, wherein the hardener is selected from a group comprising of 4,4′-Diamino-3,3′-dimethyldicyclohexyl methane (BMCHA) diethylene triamine, triethylene tetramine, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, dicyandiamide, methyl hexahydrophthalic anhydride, isophorone diamine, bis(4-aminocyclohexyl)methane, methylenedianiline or meta-phenylenediamine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1: FTIR spectra for (a) PPGEF/Cardolite NC-514 and (b) PPGEF/Cardolite NC-547 composites

[0045] FIG. 2: Differential Scanning Calorimetry curves for (a) PPGEF/NC-514 and (b) PPGEF/NC-547 composites

[0046] FIG. 3: Thermogravimetric analysis curves for (a) NC-514 and (b) NC-547 composites

[0047] FIG. 4: Storage modulus (E′) and Tan δ plots of (a) PPGEF/Cardolite NC-514 and (b) PPGEF/Cardolite NC-547 composites

[0048] FIG. 5: Scanning electron microscopy images for [0049] a) PPGEF/Cardolite NC-514 composites [0050] b) PPGEF/Cardolite NC-547 composites

[0051] FIG. 6: % Elongation verses Cardolite content for PPGEF-Cardolite composites

[0052] FIG. 7: Izod impact strength comparison for PPGEF-Cardolite composites

DETAILED DESCRIPTION OF THE INVENTION

[0053] The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

[0054] In view of above, the present invention provides novel epoxy novolac composites and process for preparation thereof.

[0055] In an embodiment, the present invention provides epoxy novolac composites comprising:

[0056] a) an epoxy novolac resin; and

[0057] b) a hardener;

[0058] c) Polyglycidyl ether of epoxy resin as flexibilizer;

characterized in that impact strength of the said composite is in the range of 24 J/m to 69 J/m.

[0059] In an embodiment, said epoxy novolac resin (a) is poly [(phenylglycidyl ether)-co-formaldehyde] (PPGEF).

[0060] In another embodiment, said wherein hardener (b) is selected from 4,4′-diamino-3,3′-dimethyldicyclohexyl methane (BMCHA), diethylene triamine, triethylene tetramine, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenylether, 4,4′-diaminodiphenylmethane, dicyandiamide, methyl hexahydrophthalic anhydride, isophorone diamine, bis(4-aminocyclohexyl)methane, methylenedianiline and meta-phenylenediamine.

[0061] In still another embodiment, said polyglycidyl ether of epoxy resin (c) is selected from di-functional glycidyl ether epoxy resin (Cardolite NC-514) and polyglycidyl ether of an alkenyl phenol formaldehyde novolac resin (Cardolite NC-547).

[0062] The Differential scanning calorimetry and dynamic mechanical thermal analysis of the composites showed a gradual decrease in glass transition temperatures (T.sub.g) with increase in cardolite content confirming the incorporation of flexible moieties into the brittle resin matrix. Improvement in toughening of PPGEF/Cardolite composites is manifested by increase in the izod impact strength of both the composites.

[0063] The tensile strength increased marginally for composites with increasing amount of Cardolite NC-514 but, decreased for the composites containing Cardolite NC-547. This is due to restricted freedom of motion in NC-547. SEM of the cryo-fractured surfaces of composites showed good compatibility between PPGEF and cardanol based flexibilizers.

[0064] In preferred embodiment, tensile strength of said composite is in the range of 63 MPa to 77 MPa.

[0065] In another preferred embodiment, the glass transition temperature (Tg) of said composite is in the range of 120° C. to 90° C.

[0066] In still another preferred embodiment, the ratio of flexibilizer to resin is in the range of 5 to 30 wt %.

[0067] In yet another preferred embodiment, the ratio of hardener to resin is in the range of 1 to 1.5 equivalents.

[0068] The Epoxy novolac composites are prepared by the reaction between PPGEF with a curing agent BMCHA in presence of Cardolite NC-514 or Cardolite NC-547. The composites with different contents of flexibilizers are prepared and examined for their structural, thermal and mechanical properties.

[0069] The FT-IR spectra of neat PPGEF, Cardolite NC-514, Cardolite NC-547 along with cured epoxy novolac composites containing different amounts of cardolites are shown in FIGS. 1(a) and 1(b). The neat PPGEF resin showed characteristic peaks at 912 cm.sup.−1 and 860 cm.sup.−1 which correspond to the oxirane rings. These oxirane ring peaks also appeared in neat Cardolite samples. The peak at 3445 cm.sup.−1 corresponds to the —OH groups of both neat PPGEF and cardolites. The C—C stretching of aromatic groups in all the samples appeared at 1508 cm.sup.−1.

[0070] The reaction between PPGEF and Cardolite in presence of curing agent BMCHA resulted into disappearance of oxirane peaks at 912 cm.sup.−1 and 860 cm.sup.−1 from the epoxy novolac composites. These observations confirmed the incorporation of cardolite flexibilizers in epoxy novolac composites.

[0071] The DSC curves of epoxy novolac composites with different loadings of Cardolite NC-514 or Cardolite NC-547 along with the neat epoxy novolac (PPGEF) are shown in FIGS. 2(a) and 2(b). The decrease in T.sub.g may be attributed to the flexibilizing effect of the cardolites. Although the cardolites are chemically linked to the novolac epoxy by crosslinking, the value of T.sub.g is not altered.

[0072] Thermal degradation of neat PPGEF and epoxy novolac composites with cardolite flexibilizer is studied by thermogravimetric analysis in the air atmosphere. The TGA curves of neat resin (PPGEF) and the epoxy novolac composites with different contents of Cardolite NC-514 and Cardolite NC-547 are shown in FIGS. 3(a) and 3(b) respectively.

[0073] The FIGS. 3(a) and 3(b) shows that all the composites have shown one-step degradation. Tables 2(a) and 2(b) show the results of TGA for PPGEF/Cardolite NC-514 and PPGEF/Cardolite NC-547 composites. It is observed that the char residue at 600° C. (char yield) is slightly higher in the case of epoxy novolac with Cardolite NC-547 which may be due to more number of aromatic rings present in the Cardolite NC-547.

[0074] The storage modulus (E′) and the tan δ values of the cured neat epoxy novolac composite and epoxy novolac composites containing 5, 10, 20, 30 wt % of Cardolite NC-514 and Cardolite NC-547 as a function of temperature are shown in FIGS. 4(a) and 4(b). A single glass transition temperature (T.sub.g) with a clear rubbery plateau region is observed. The storage modulus decreased gradually with the addition of cardolite revealing the increased flexibility of the epoxy novolac composites. The storage modulus also dropped with increasing temperature and passed through T.sub.g region before reaching the rubbery plateau, where the segmental motions of the network chain occur cooperatively

[0075] The incorporation of Cardolite NC-514 and Cardolite NC-547 flexibilizers in novolac epoxy resins affected the mechanical properties of the final cured epoxy novolac composites. The results are summarized in Table 3. The results show that in the case of composites with Cardolite NC-514, the tensile and impact strength increased with increase in cardolite content from 5 to 30 wt %. However, there is hardly any change in the % elongation w. r. t. increase in cardolite content. While the tensile strength increased by 5-6%, more effect of flexibilizer was seen in impact strength which increased from 31.7 J/m to 68.6 J/m with Cardolite NC-514 content from 5 to 30 wt %. The increase in impact strength may be attributed to the presence of flexible chains in the backbone of the Cardolite NC-514, which can absorb an appreciable amount of energy under the impact.

[0076] The SEM images of the cryo fractured specimens for cured neat and cardolite incorporated epoxy novolac composites are shown in FIG. 5. The specimens are scanned at a magnification of 1K. The fractured surface of the neat composite [FIG. 5(a.1) or 5(b.1)] shows a very smooth and plain morphology, which indicate that the fracture is brittle. In all the scanned images, no phase separation is observed which clearly indicates the compatibility of PPGEF and Cardolite NC-514/Cardolite NC-547. The figures FIG. 5(a) (2-7) shows that the fracture is ductile for the PPGEF/Cardolite NC-514 composites influenced by the incorporation of Cardolite NC-514. For PPGEF/Cardolite NC-547 composites the FIG. 5(b) (2-7) shows the fractured surfaces indicate the homogeneity of PPGEF and Cardolite NC-547 upon curing.

[0077] In another embodiment, the present invention provides a process for preparation of epoxy novoloc composite comprising: [0078] a. Mixing epoxy novolac resin with bio-derived modifierin different amounts ranging from 5% to 30% per hundred resin (phr) varying by 5% in each composition to obtain mixture; [0079] b. Adding hardener to the mixture of step (a) to obtain the composite.

[0080] In preferred embodiment, said epoxy novolac resin is poly [(phenylglycidyl ether)-co-formaldehyde] (PPGEF).

[0081] In another preferred embodiment, said bio-derived modifier is polyglycidyl ether of epoxy resin which is selected from di-functional glycidyl ether epoxy resin (Cardolite NC-514) and polyglycidyl ether of an alkenyl phenol formaldehyde novolac resin (Cardolite NC-547).

[0082] In still another preferred embodiment, the present invention provides a process for preparation of composition wherein the hardener is selected from the following: 4,4′-diamino-3,3′-dimethyldicyclohexyl methane (BMCHA) diethylene triamine, triethylene tetramine, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, dicyandiamide, methyl hexahydrophthalic anhydride, isophorone diamine, bis(4-aminocyclohexyl)methane, methylenedianiline or meta-phenylenediamine The process for the preparation of epoxy novoloc composite is as shown in below scheme 1:

##STR00001## ##STR00002##

EXAMPLES

[0083] The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

Example 1: Preparation of Composites with Cardolite NC-514

[0084] Epoxy novolac composites were prepared by two step mixing process. Initially, PPGEF was mixed with Cardolite NC-514 in a beaker in different amounts ranging from 5-30% per hundred resins. To this mixture, a stoichiometric amount of BMCHA was added. The composite was thoroughly mixed and vacuum was applied to remove the entrapped air bubbles. All the mixing was performed at ambient temperature. It was then poured in greased PTFE mould following the cure schedule of 80° C./1 h and further 120° C./4 h. The mould was cooled and the cured specimens were taken out for further characterization. Similarly, epoxy novolac composites with Cardolite NC-514 were prepared by varying its content upto 30% per hundred PPGEF. The sample code for example is denoted as follows: NC-514-00 corresponds to the neat epoxy novolac composite. NC-514-05 corresponds to the composites containing 5% Cardolite etc.

TABLE-US-00001 (Composition) Sample code NC- NC- NC- NC- NC- NC- 514- 514- 514- 514- 514- 514- Ingredients 05 10 15 20 25 30 PPGEF 1 1 1 1 1 1 (equivalents) BMCHA 1.5 1.5 1.5 1.5 1.5 1.5 (equivalents) Cardolite NC-514 5 10 15 20 25 30 (%)

Example 2: Preparation of Composites with Cardolite NC-547

[0085] Epoxy novolac composites using Cardolite NC-547 were prepared in a similar way as described in example 1 by two step mixing process. Initially, PPGEF was mixed with Cardolite NC-547 in a beaker in different amounts ranging from 5-30% per hundred resin. To this mixture, a stoichiometric amount of BMCHA was added. The composite was thoroughly mixed and vacuum was applied to remove the entrapped air bubbles. All the mixing was performed at ambient temperature. It was then poured in greased PTFE mould following the cure schedule of 80° C./1 h and further 120° C./4 h. The mould was cooled and the cured specimens were taken out for further characterization. Similarly, epoxy novolac composites with Cardolite NC-547 were prepared by varying its content upto 30% per hundred PPGEF. The sample code for example is denoted as follows: NC-547-00 corresponds to the neat epoxy novolac composite. NC-547-05 corresponds to the composites containing 5% Cardolite etc.

TABLE-US-00002 (Composition) Sample code NC- NC- NC- NC- NC- NC- 547- 547- 547- 547- 547- 547- Ingredients 05 10 15 20 25 30 PPGEF 1 1 1 1 1 1 (equivalents) BMCHA 1.5 1.5 1.5 1.5 1.5 1.5 (equivalents) Cardolite NC-547 5 10 15 20 25 30 (%)

Example 3: Characterization of Composites

[0086] A. Fourier Transform Infrared Spectroscopy (FT-IR):

[0087] FT-IR spectra of the composite films were recorded on a Perkin Elmer Spectrum GX FT-IR spectrometer in the range of 4000 to 750 cm.sup.−1 with a resolution of 4 cm.sup.−1. The measurements were performed in the ATR mode.

[0088] The FT-IR spectra of neat PPGEF, Cardolite NC-514, Cardolite NC-547 along with cured epoxy novolac composites containing different amounts of cardolites are shown in FIGS. 1(a) and 1(b). The neat PPGEF resin showed characteristic peaks at 912 cm.sup.−1 and 845 cm.sup.−1 which correspond to the oxirane rings. These oxirane ring peaks also appeared in neat Cardolite samples. The peak at 3445 cm.sup.−1 corresponds to the —OH groups of both neat PPGEF and cardolites. The C—C stretching of aromatic groups in all the samples appeared at 1608 cm.sup.−1.

[0089] The reaction between PPGEF with a curing agent BMCHA in presence of Cardolite resulted into disappearance of oxirane peaks at 912 cm.sup.−1 and 845 cm.sup.−1 from the epoxy novolac composites. These observations confirmed the incorporation of cardolite flexibilizers in epoxy novolac composites.

[0090] B. Differential Scanning Colorimetry (DSC):

[0091] DSC experiments were performed using DSC Q10 TA Thermal Analyzer using aluminum sample pans. The samples were heated from 25° C. to 225° C. with a heating rate of 10° C./min in the nitrogen atmosphere with a flow rate of 50 ml/min. Glass transition temperature (T.sub.g), curing temperature and extent of curing were studied from the DSC thermograms.

[0092] The DSC curves of epoxy novolac composites with different loadings of Cardolite NC-514 or Cardolite NC-547 along with the neat epoxy novolac (PPGEF) are shown in FIGS. 2(a) and 2(b). It can be readily seen that all the samples exhibited single T.sub.g indicating no phase separation. The neat epoxy novolac resin (PPGEF) showed the T.sub.g of 120° C. Upon incorporating cardolites, the decrease in T.sub.g was observed with increasing amounts of cardolites. A similar trend was observed in the DMTA measurements also (see Table 1). The decrease in T.sub.g can be attributed to the flexibilizing effect of the cardolites. Although the cardolites were chemically linked to the novolac epoxy by crosslinking, the value of T.sub.g did not alter. It may be due to the fact that the flexibility of the cardolite is more dominant as compared to the crosslinking of PPGEF.

[0093] It was also observed that in the case of Cardolite NC-514, the T.sub.g decreased from 120° C. (neat PPGEF) to 90° C. (30 wt % Cardolite NC-514) upon incorporating cardolite NC-514. Whereas, the decrease in T.sub.g with Cardolite NC-547 (30 wt % Cardolite NC-547) was only up to 100° C. The relatively more decrease in T.sub.g with Cardolite NC-514 at the same loading can arise from more flexible nature of Cardolite NC-514 in which the flexible chain is situated in the backbone of the cardolite chemical structure. On the other hand, Cardolite NC-547 contains flexible groups in the side chain of the backbone and might induce less flexibility to the epoxy novolac composites. Further, Cardolite NC-547 with more number of epoxide groups can lead to more crosslinking during the curing reaction resulting in the overall decrease of flexibility of Cardolite NC-547 incorporated epoxy novolac composites. These observations were clearly seen in the DSC studies.

TABLE-US-00003 TABLE 1 T.sub.g from DSC and DMTA analysis for PPGEF/NC-514 and PPGEF/NC-547 composites T.sub.g from tan δ peaks T.sub.g by DSC (° C.) DMTA (° C.) Car- PPGEF/ PPGEF/ PPGEF/ PPGEF/ dolite Cardolite Cardolite Cardolite Cardolite Sr. Content NC-514 NC-547 NC-514 NC-547 No. (Wt. %) composites composites composites composites 1. 00 120 120 128 128 2. 05 110 116 122 121 3. 10 108 112 120 119 4. 15 106 109 119 119 5. 20 102 108 116 118 6. 25 100 106 115 117 7. 30 90 100 112 116 C. Thermogravimetric Analysis (TGA)

[0094] TGA measurements were performed on a Perkin Elmer STA 6000 thermogravimetric analyzer. Around 10-15 mg sample was placed in a ceramic crucible and heated from 25° C. to 600° C. at a heating rate of 10° C./min in an air atmosphere with a flow rate of 30 ml/min. The initial decomposition temperature at 5% weight loss (T.sub.5%), the temperature at which maximum degradation occurs (T.sub.max %), the temperature where 50% decomposition occurs (T.sub.50%) as well as char residue at 600° C. were noted from TGA thermograms.

[0095] Thermal degradation of neat PPGEF and epoxy novolac composites with cardolite flexibilizer was studied by thermogravimetric analysis in the air atmosphere. The TGA curves of neat resin (PPGEF) and the epoxy novolac composites with different contents of Cardolite NC-514 and Cardolite NC-547 are shown in FIGS. 3(a) and 3(b) respectively.

TABLE-US-00004 TABLE 2 (a) Results of TGA in Air of PPGEF/Cardolite NC-514 composites Sr. T.sub.5% T.sub.50% T.sub.max% Char residue No. Sample code (° C.) (° C.) (° C.) @ 600° C. (%) 1. NC-514-00 (neat) 342 420 470 0 2. NC-514-05 343 425 476 3 3. NC-514-10 337 424 478 3 4. NC-514-15 337 422 478 4 5. NC-514-20 336 391 477 3 6. NC-514-25 344 393 478 3 7. NC-514-30 341 395 475 3

TABLE-US-00005 TABLE 2 (b) Results of TGA in Air of PPGEF/Cardolite NC-547 composites Sr. T.sub.5% T.sub.50% T.sub.max% Char residue No. Sample code (° C.) (° C.) (° C.) @ 600° C. (%) 1. NC-547-00 (neat) 342 420 470 0 2. NC-547-05 341 393 476 4 3. NC-547-10 336 401 482 4 4. NC-547-15 340 396 476 5 5. NC-547-20 334 390 474 3 6. NC-547-25 331 395 475 3 7. NC-547-30 341 399 482 2

[0096] It can be seen from the figure that all the composites have shown one-step degradation. Tables 2(a) and 2(b) show the results of TGA for PPGEF/Cardolite NC-514 and PPGEF/Cardolite NC-547 composites. The 5% weight loss temperature (T.sub.5%) that corresponds to the temperature when 5% of initial weight was lost, decreased with an increase in the cardolite content. However, the decrease was not significant. The major weight loss was found to occur in the temperature range of 300-500° C. in all the epoxy novolac composites. About 50% degradation occurs at around 400° C. which is denoted as T.sub.50%. The maximum degradation was observed in the temperature range of 470-480° C. due to the oxidative degradation in the presence of air. It was also observed that the char residue at 600° C. (char yield) was slightly higher in the case of epoxy novolac with Cardolite NC-547 which may be due to more number of aromatic rings present in the Cardolite NC-547.

[0097] D. Dynamic Mechanical Thermal Analysis (DMTA)

[0098] Dynamic Mechanical Thermal Analysis (DMTA) studies were performed on a Rheometric Scientific DMTA dynamic mechanical analyzer to evaluate the viscoelastic properties of the epoxy novolac composites. In the dynamic mode, the samples were heated from 40° C. to 150° C. with a heating rate of 10° C./min. Three point bending method was used at a frequency of 1 Hz. Storage modulus (E′) and loss tangent factor (tan δ) were recorded as a function of temperature. The dimensions of the samples were (25×10×1) mm.

[0099] The storage modulus (E′) and the tan δ values of the cured neat epoxy novolac composite and epoxy novolac composites containing 5, 10, 20, 30 wt % of Cardolite NC-514 and Cardolite NC-547 as a function of temperature are shown in FIGS. 4(a) and 4(b). A single glass transition temperature (T.sub.g) with a clear rubbery plateau region is observed. The storage modulus decreased gradually with the addition of cardolite revealing the increased flexibility of the epoxy novolac composites. The storage modulus also dropped with increasing temperature and passed through T.sub.g region before reaching the rubbery plateau, where the segmental motions of the network chain occur cooperatively.

[0100] It can be clearly seen from the figure that, plots of loss tangent (tan δ) gave single peak which indicated that there was no phase separation in the cured epoxy novolac composition. With respect to temperature, tan δ changed slightly that corresponds to T.sub.g. The decrease in T.sub.g with an increase in cardolite content indicated the flexible nature of novolac epoxy composites which are otherwise brittle in nature. The T.sub.g values obtained from DMTA are shown in Table 1.

[0101] E. Tensile Strength and Izod Impact Strength

[0102] Tensile strength and % elongation values were determined using an Instron Universal testing machine as per the standard ASTM D 638-V. A 10 kN load cell was used for measuring the load and a constant cross head speed of 5 mm min.sup.−1 was maintained. At least five dog bone shaped specimens were prepared for each type of composite in mild steel mould and average value was considered.

[0103] The impact energies absorbed by the composites were measured on Ceast izod impactor. The specimens were prepared as per the standard ASTM D 256-02. At least five specimens were prepared for each composition and an average value was considered.

[0104] The incorporation of Cardolite NC-514 and Cardolite NC-547 flexibilizers in novolac epoxy resins affected the mechanical properties of the final cured epoxy novolac composites. The results are summarized in Table 3. It can be found that in the case of composites with Cardolite NC-514, the tensile and impact strength increased with increase in cardolite content from 5 to 30 wt %. However, there was hardly any change in the % elongation w. r. t. increase in cardolite content. While the tensile strength increased by 5-6%, more effect of flexibilizer was seen in impact strength which increased from 31.7 J/m to 68.6 J/m with Cardolite NC-514 content from 5 to 30 wt %. The increase in impact strength could be attributed to the presence of flexible chains in the backbone of the Cardolite NC-514, which can absorb an appreciable amount of energy under the impact. A moderate increase in the tensile strength of the composites with Cardolite NC-514 may be due to the rotational motion around the flexible —CH.sub.2 groups and shear yielding which may result into strain hardening. On the contrary, in the case of novolac epoxy composites with Cardolite NC-547, the tensile strength decreased from 71.5 MPa (neat epoxy composite) to 63.6 MPa (with 30 wt % Cardolite NC-547).

TABLE-US-00006 TABLE 3 Mechanical properties of PPGEF/Cardolite NC-514 and NC-547 composites Tensile Impact strength Elongation strength Sr. No. Samples (MPa) (%) (J/m) Neat PPGEF composite 1. Neat 71.5 2.46 24.5 PPGEF/Cardolite NC-514 2. NC-514-10 72.4 2.93 33.3 3. NC-514-20 74.3 3.02 42.4 4. NC-514-30 76.2 2.72 68.6 PPGEF/Cardolite NC-547 5. NC-547-10 68.9 2.60 36.9 6. NC-547-20 64.1 2.88 40.8 7. NC-547-30 63.7 2.15 53.3

[0105] The decrease in tensile strength could be attributed to the hindered rotational motion in the chain as a result of the close proximity of rigid phenyl groups. Further, the increase in impact strength was less as compared to the composites containing Cardolite NC-514. This could be due to the less flexible nature of Cardolite NC-547.

[0106] F. Scanning Electron Microscopy (SEM)

[0107] The surface morphology analysis was performed on SEM Leica-440 scanning electron microscope at ambient temperature. The cryo fractured cured composite specimens were gold sputter coated prior to scanning.

[0108] The SEM images of the cryo fractured specimens for cured neat and cardolite incorporated epoxy novolac composites are shown in FIG. 5. The specimens were scanned at a magnification of 1K. The fractured surface of the neat composite [FIG. 5(a.1) or 5(b.1)] shows a very smooth and plain morphology, which indicate that the fracture is brittle. In all the scanned images, no phase separation was observed which clearly indicates the compatibility of PPGEF and Cardolite NC-514/Cardolite NC-547. This can also be confirmed from the single T.sub.g peaks obtained in DSC and DMA measurements. It can be seen from FIG. 5(a) (2-7), the fracture is ductile for the PPGEF/Cardolite NC-514 composites influenced by the incorporation of Cardolite NC-514. For PPGEF/Cardolite NC-547 composites [FIG. 5(b) (2-7)], the fractured surfaces indicate the homogeneity of PPGEF and Cardolite NC-547 upon curing.

ADVANTAGES OF THE PRESENT INVENTION

[0109] Effective toughening of brittle epoxy novolac resin (PPGEF) using cardanol based epoxy resins (Cardolite NC-514 and Cardolite NC-547) used as modifiers. [0110] Bio-derived materials; may give better strength and toughening.