R Yadav, D Srivastava - Studies on cardanol-based epoxidized novolac resin and its blends - страница 2

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Results of TG/DTG traces of unmodified and CTBN-modified cardanol-based epoxidized novolac resins

cured with polyamine

Blend

 

First step

 

 

 

Second step

 

Total % CY

sample

T

T

1 max

T

%CY

T

T

1 max

T

%CY

 

ECF52

465

589

616

49.3

616

711

771

47.2

3.5

ECFxi

451

592

626

62.6

626

702

787

34.4

3.2

ECF522

441

599

630

90.7

630

713

772

7.0

2.3

ECF523

449

578

628

53.8

628

711

764

42.1

4.1

ECF524

472

595

628

55.6

628

714

778

40.5

3.9

Note: To - onset temperature of degradation; Tm char yield.

- temperature of maximum rate of mass loss; T - extrapolated final decomposition

temperature; CY

3.7 Thermal stability

The systems were evaluated for the thermal stability in nitrogen atmosphere by thermogravimetric analysis. The thermogravimetric results (TG) obtained for samples ECF52 and ECF523 are shown in Figs. 11 and 12 for the evaluation of thermal stability in the nitrogen atmosphere. The onset temperature of degradation (To), temperature of maximum rate of mass loss (Tmax) and extrapolated final decomposition temperature (Tf) were noted from TG traces and are pre­sented in Table 3. TG analysis confirmed the occurrence of samples degradation. The degradation of the blend systems was found to occur in two steps. The temperature of 5 % weight loss increased slightly from 567 K for pure epoxy (sample ECF52) resin to 573 K for the epoxy/CTBN blend (i.e. blend sample ECF523). The addition of the appropriate amount of epoxy could decrease the mobility and increase the stability of CTBN via the reaction between the thermal carboxyl group of CTBN and hydroxyl group of epoxy [33-36].

3.8. Scanning electron microscopic analysis

Figs.13 and 14 show the SEM micrographs of fractured surface of the pure epoxy and CTBN modified epoxy matrix respectively. SEM of CTBN modified system showed the presence of precipitated, discrete rubber particles, which were dispersed throughout the epoxy matrix, i.e. they revealed the presence of two-phase morphological features. The soft elastomeric phase was separated from the hard epoxy matrix during the early stage of the cure. The fractured surface of the most of the rubber-toughened epoxy system has a rigid continuous epoxy matrix with a dispersed rubbery phase as isolated particles [37]. Some cavitations of the rubber particles accompanied by stress whitening zones were also observed in the scan (Fig.14). This stress whitening effect may be related to the location deformation at the crack tip. Furthermore, the cavitations were followed by the onset of the shear localization process [38-40] resulting in the observed increase of thermal properties.

4. Conclusions

DSC studies showed the exothermal heat of epoxy crosslinking reaction due to addition of rubber into epoxy

0.1

S -OJ

5

273

323

373 413 Temperature (К)

4~3

523

Fig. 9. DSC scan of epoxidized novolac resin ECF52

373 423

Temperature (K)

Fig. 10. DSC scan of blend sample BECF

523

273        473       673        873       1073 1273 Temperature (K)

Fig. 11. TGA Trace of blend sample ECF52

Fig. 13. SEM micrographs of preapared sample ECF52

Fig. 14. SEM micrographs of preapared sample BECF523

matrix. The thermal stability of the cardanol based epoxy resin was increased with the addition of 15 wt% CTBN in the epoxy matrix. Cardanol-based epoxy network modified with CTBN displayed two phase separated morphology with dispersed rubber globules in the matrix resin.

Acknowledgements

This work was sponsored by Council of Science and Technology, UP, Lucknow. We, also, thankfully acknowledge the contributions rendered by M/s Satya Cashew Pvt. Ltd., Chennai for providing cardanol and M/ s Emerald Performance Materials, LLC, Hong Kong for providing CTBN.

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ВИВЧЕННЯ ЕПОКСИДНИХ НОВОЛАЧНИХ СМОЛ НА ОСНОВІ КАРДАНОЛУ ТА ЇХ СУМІШЕЙ

Анотація. Синтезовано фенольну новолачну смолу на основі карданолу з мольним співвідношенням карда-нол: формальдегід 1.0:0,5 з використанням як каталізатор дикарбонової кислоти, зокрема янтарної. Таку смолу у подальшому модифікували надлишком епіхлоргідрином при 393 К у лужному середовищі. Вивчені у різному масовому співвідношенні суміші дигліциділового етеру бісфенолу А і полігліцидної новолачної смоли з кополімером бутадієну з акрилонітрилом, що містить кінцеві карбоксильні групи (БАКК). Як структуруючий агент таких сумішей використаний поліамін у стехіометричній кількості стосовно епоксидних груп. Формування зшитих структур вищеназваних сумішей вивчено різними методами ІЧ-спектроскопічного аналізу. . Середньомолекулярну масу визначали гель-хроматографією. Встановлено, що мінімальна тривалість структурування і найвища термічна стабільність систем спостерігається при вмісті в таких сумішах 15 % мас. БАКК.

Ключові слова: карданол, формальдегід, новолак, епіхлоргідрин, епоксидна смола, бутадієн-акрилонітриловий кополімер, спектральні методи.

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R Yadav, D Srivastava - Studies on cardanol-based epoxidized novolac resin and its blends