Epoxy resin can be reinforced with glass (fabric form) in presence of Vulkadur-A, a phenol formaldehyde resin containing a hardening agent. Overall enhancement in mechanical properties has been found stocks cured with Vulkadur-A containing 2.5 parts of carbon black as filler

Banerjee, S.

Ghosh, T. K.

English

Defence Science Journal

*The bauds at f + 6 0 0 ~ ) - ~  and 910 c q 1  were attributed to epoxy J Acc. Na-_, f STUDIES ON GLASS REINFORCED EPOXY RESIN USING VULKADUR-A AS CROSSLINKING AGENT BOTH IN PRESENCE AND ABSENCE OF CARBON BLACK AND OTHER NON-BLACK FILLERS / T. K. GHOSH & S. BANERJEE Indian Institute of Technology, Kharagpur (Received 13 June 1972; reuised 16 August 1973) Epoxy resin can be reinforced with glass (fabric forrn);n presence of Vulkadur-A, a phenol formaldehyde resin con- ttining a h d e n i n g  agent. Overall enhancement in mechanical properties has been found with stocks cured with Vulkadur-A containing 2 .5  parts of carbon black as filler. The choice of matrix resin in reinforced plastics is a matter of prime importance, since on it depend, many properties such as strength, ease of fabrication, resistance to service conditions (temperature, humi- dity etc.) and cost. Attempts have been made to utilise various types of resins to improve, particularly, the quality of the existing structural materials and to replacd various other materials of general interest. In this work, investigation on reinforcement of epoxy resin (Araldite CY & 230) with glass (fabric form) both in presence of carbon black and non-black materials as fillers and also ih their absence has been carried out by measuring different mechanical properties of the composites. Infra-red spectra have been taken in case of unfilled stocks and a reaction scheme has been suggdsted to correlate the mechanical properties with the data obtained from spectral analysis. M A T E R I A L S  A N D  M E T H O D S  Araldite CY 230-It is an epoxide resin obtained from CIBA of India Ltd., Bombay. Vulkadur-A-It is a Phenol, Formaldehyde resin containing a hardening agent obtained from Bayer (India) Ltd,, Bombay. < Carbon Black (SRF)-A product of Cabet, U.S.A. Alumini~m Oxide and Silica-These were of a chemically pure grade. Glam Fabric-It was of a quality given in Table 1 and obtained from Fibre glass Pilkington Ltd., Bombay. Lamimte'o~z Laminates were fabricated with heat cleaned woven ' glass fabric3 and cured in a big david bridge curing press under heat and pressure. Mechanical properties of the composites namely tensile strength, hardness and 'OoO- ARALD"E Cy 230+VULKADuR-At5r' WTa bursting load were measured by known methods.1 LAMINATING PRESSURE =20 UQISV cm NO. OF P L Y S = ~  Ififrared Spectra 2600- I.R. spectra* were taken with udlled stock cured e at 100" C for different cure times. r \ R E S U L T S  A N D  D I S C U S S I O N  d The variation of tensile strength, Brine11 hardness 2 0 0 0  - and bursting Ioad with cure time at different tempera- tures is given in Fig. 1-3. The maximum values of E tensile strength and bursting load at 180°C and 100°C 5 TABLE 1 w J QUALITY OF GLASS BABRIC U) Z1000 ~.-H-_^I- 2 0  3 0  4 0  60  8 0  I 2 0  180 CURE TIME (MIN.) . Fra 1-Variation of tensile strength with cure time at various cure temperatures for glass fabric epoxy resins composites. .-. - . W T y P i ~  glass . ---.+- : . Desiw . ---- Thrmds per inch E ---.------ 4 om. (Appx.) irc-c-h- Plain weave Dm. SOI. J., VOL. 24, Apm 1974 ARALDITE CY 2 3 O t  VULKADUR - A= 5:I BY WT. LAMINATING PRESSURE = 2 0  KG.ISq;.C* LAMINATING PRESSURE=20 KG. IS% Cm. No. OF PLYSs6 No. O F  PLYS=6 5 1 . - *  1 0  2 0  3 0  4 0  6 0  80  120 CURE T I M E  (MIN.) CURE TIME (MIN.) h o  2-Variation of Brine11 hardness with cure time at FIU 3-variation of bursting load with cure time at various femperatures for glass fabric epoxy resin various cure temperatures for glass fabric composites. epoxy resin composites. I ! are practically the same and they occur almost at  the same cure time at  each temperature and, as is ex- pected, the optimum cure time is much greater at  100°C. The curves at  l6O0C, however, show a peculiar behaviour which may be explained thus : The curing s f  the resin may occur in two stages, The second stage may involve some of the reaction products of the first stage and occurs appreciably at higher temperature. Highkr temperatures also cause a, degradation of the uncured resin. At 100°C, the second stage is almost absent, so it is only after prolonged heating that the finally curedmass is obtained. At 180°C, due to rapidly occuring second stage curing, the final product is obtained before the thermal degradation is appreciable. A% intermediate temperatures, the degradation and the second stage curing proceed simuItaneously with equivalent rates and that is why the properties are less developed and there is no maximum in the bursting load curve in Fig. 3. Other features are more or less similar to those reported in our earlier communicationl. In case of carbon black filled stock, .(Pig. 4) maximum tensile strength has been found wit#h stock con - taining 2-5  parts of carbon black cured at  60 minutes as in case of u d l e d  one; but the value is higher than 1000 I- 1 5 00 /"--""- I 0  2 0  3 0  4 0  6 0  80 ' 2 0  I0 2 0  3 0  4 0  60  8 0  120 CURE TIME (MIN 1 CURE TIME (MIN.) Eko 4-Variation of tensile strength with cure time for FIU 5-Variation of tensile strength with cure time for glass fabric epoxy resin composites containing glass fabric epoxy resiq composites containing different pa& of oarbon black (SRF) as fillers. fillers (Filler contents 2.6 phr). 3 0 0 0 1  - e E Y, - d V 2 0 0 0 -  0 5 a 5 W -I- 2 W I- ARALDITE CY 2 3 0  + VULKADUR - A 5: 1 BY WTe. 3 0 0 0 -  ARALDITE CY 230fVULKADUR - A  = 5.1 BY WT. LAMINATING PRESSURE=%O KG.IS% Cm. LAMINATING PRESSURE = 2 0  KG.IS9. Cm. CURE TEMR =I~O'C CURE TEMR =180°c No. OF PLYS 2 6  E N s  OF PLYS= 6 U 4 Z . ci 2 5 0 0 -  Y m z W I- I Gaos~ & BANWBID :Studies on Glass Wiorced Epoxy Resin that of the latter. Moreover, the fall in tensile strength after attainment of maximum is not so steep as in case of unfilled stock. It is also evident from Fig. 4 that as carbon black increases there is an overall decrease in tensile strength and its maxima shifts towards higher values of cure time. The higher value of maximum tensile strength and its slow fall after attainment of maximum may be due to high surface activity of carbon black which causes stiffening of the polymer by holding two or more chains on their surfaces thus functioning as additional crosslinks. Further, its good disper8ion in the resin matrix may facilitate transfer of stress to the neighbouring chains in the event of rupture of one chain re- sulting in high tensile strength values a t  optimum cure time and onwards. Moreover, it has been found by McBarry et a12 that precipitated particles of elastameric material, distributed throughout the crosslinked resin matrix in a fibrous glass reinforced epoxy resin composite, act as toughening agent against cracking. Carbon black with chemisorbed polymer chain on its surface may also be effective as a toughening agent to some extent against cracking in the composite as a whole. The increase in parts of carbon black increases the probability of getting unreacted carbon black particle in the composite, which causes many discontin- uities in the resin phase as in case of non-black filled stock and thus i t  ultimately reduces the tensile strength values. The shifting of maximum tensile strength values towards higher cure time with increase in parts of carbon black in the composite is due to the faot that carbon black may have some retarding influence on the rate of cure and it increases with increase in its content in the stock. This retardation with 7.6 phr is so great that the rnaximum value in the curve is almost suppressed. In ease of stocks containing silica and AZPO3 as fillers as shown in Fig. 5, it is evident that tensile strength values fall from tbe very beginning in both the cases. This shows that the fillers are not reactingin any way with the resin matrix. Moreover, their mere presence produces many discontinuities in the resin phase. In case of bursting load with stocks containing different parts of carbon black, Fig. 6, i t  is found that maximum bursting load values shift towards higher values of cure time with increase in carbon black filler content. This was also so in case of tensile strength (Rg. 4). The reason is same as discussed therein. Here, the steep rise and fall in all the cases unlike those of tensile strength clearly indicates that carbon black is a good reinforcing agent for the resin. Bursting load values in case of stocks containng A2,0, and silica as fillers (Fig. 7) have been found to decrease a t  a rapid rate compared to fall in tensile strength values with the same stock (Fig. 5). This is obvious because bursting is much dependent on the resin matrix which contains many discontinuities due , to presence of these inactive fillers in the composite. ARALDITE CY 23O+ VULKADOR -A * 531 BY WT* LAMINATING PRESSURE - 2 0  KG, ISqr  Cm. CURE TEMP.= I~O~C No. Of PLYSZ6 7-- "0!0 i0  h i 0 '  6 0  8 0  120 CURE TIME (MIN.) Fra &Variation of bursting load with cure time for ' glass fabric epoxy resin composites containing difhrent parts of carbon black (BPI?). 8 0 0 -  ARALDITE CY 23O*VULUADUR - A s  5:l BY % LAMINATING PRESSURE - 2 0  K G J S ~  C m  . CURE TEMR-I~O~C No. OF PWSrd 7 0 0 .  3 1 4 -  300;o i o  ;O o 6 0  8 0  120 CURE TIME (MIN ) Fra 7-Variation of bmting load with oure time for glass fabric epoxy resin composites containing differept fillers (Fillers contents 275 phr). DEB S ~ I .  J., VOL. 24, APRIL 1974 (a UNCURhD ARALblTE CY 230  W w (b) CURE TfME=120 MtW. W u. fi z 4 Q m a a $ S 9 m e (C) CURE fJME= 240 MIN. I I ' ~ ' I ' ~ ' 1 ' ' ~  3200 2 4 0 0  1600 8 0 0  2 0 e  I . 4000 32b0 2200 &0 8 2 0 0  * .  d FREQUENCY (~rn-l) FREQUENCY ( c ~ ' )  FIG 8-IR Spectrum of (6) uncured Araldite CY FIG 9-IR Spectra of cured Araldite CY 230 containing 230 (b) Vulkadur-A, and (c) Araldite CY 230 Vulkadur-A, cure time (a)60 minutes (b) 120 minutes cured with Vulkadur-A, (cure time 20 minutes). (c) 240 minutes. Spectral ~ n a l ~ s i s  and Reaction Scheme , IR  spectra have been taken in case of stocks cured a t  100°C for different cure times (Fig. 8 & 9). It has been found that a t  20 minutes of cure time almost all the epoxy groups are exhausted in addition to diminu- tion of all other reacting groups. Incidentally, the tensile strength also becomes higher at 20 minutes of cure time. The reaction scheme as suggested in our earlier communieationl correlates the mechanical data ob- tained with those from spectral analysis. The subsequent fall in tensile strength values upto 40 minutes of cure time may be due to partial breakdown of the products in addition to decomposition of the epoxy resin, leading to the evolution of gases like ammonia, methylamine and CHzO and formation of methylene- bridged compounds. The evolved gases may also give rise to voids in the structure and thereby weaken it. . The increase in tensile strength values from 40 minutes of cure time to 80 minutes of cure time may be die  to formation of further cross-linked productil. The final fall after 80 minutes of cure time can be attributed to ultimate deterioration of the cured product. The steep rise in tensile strength at higher temperature and its earlier attainment of maxima and subsequent falling down is due to enhancement of the rate of cure and rate of deterioration at higher temperature. C O N C L U S I O N S  Maximum values of tensile strength, hardness and bursting load have been found with stock cured a t  180°C for 60 minutes of cure time (Pig. 1-3). The same maximum values of tensile strength and bursting load have also been found with stock cured at 100°C for 80 minutes (Pig. 1 & 3). In case of filled stock containing TABLE 2 2-5  parts of carbon black, it has been found that MAXIMUM TENSILE STRENGTE, IIARDNESS AND BURSTING LOAD tensile strength and bursting load have increased. VALUES FOR BILLED AND UNFILLED STOCKS In all other cases there was deterioration in all Stock Filled Unfilled tensile strength and bursting load values. The su- perior performance of carbon black in lower proportion may be ascribed to the adsorption of resins on the surface acting as additional cross-linkings; but with higher proportion of carbon black or with other fillers, due to non-compatibility the fillers act as discontinuities in the resin matrix and thereby weaken it. Maxi- mum tensile strength, hardness and bursting load values as found both in case of filled and unfilled stock are given in Table 2. R E F E R E N C E S  1. G R O S ~ ,  T. K. & BANIDRJEE, S., J. Materials Sci. London 8, (1972), 915-923, 2. FBPDBIcK, J., MOGARBY & ANDRE M. WILLNEB, Amer. Chem. Soo., Div. Polym. Chem., 8, (1967), 2,1056-5iJ , 56 ~~~~~i~~ load (kglcm2) -725'00 703.10 the properties due to incorporation of fillers. .It has been found that lower contents of carbon black have some reinforcing'action whereas higher contents show some retarding effect on the overall curing process and reduce otrerall Tensile strengtb (kglcmP) 2800- 00 2585' 00 ~ ~ i ~ l l  hardness (kp,!-ma) --,-,-,-.-.---,------- - 19.89 

Studies on Glass Reinforced Epoxy Resin Using Vulkadur- A as Crosslinking Agent both in Presence and Absence of Carbon Black and other Non black Fillers

https://publications.drdo.gov.in/ojs/index.php/dsj/article/download/6506/3562

Studies on Glass Reinforced Epoxy Resin Using Vulkadur- A as Crosslinking Agent both in Presence and Absence of Carbon Black and other Non black Fillers

Abstract

Similar works

Full text

Available Versions

Defence Science Journal