Editorial Type:
Article Category: Research Article
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Online Publication Date: 01 Dec 2015

PROBING THE POSTGELATION REACTIONS OF EPOXIDIZED NATURAL RUBBER CROSS-LINKED WITH DODECENYL SUCCINIC ANHYDRIDE

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Page Range: 560 – 573
DOI: 10.5254/rct.15.84888
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ABSTRACT

Pregelled mixes of an epoxidized natural rubber, known as ENR50, containing dodecenyl succinic anhydride (DDSA) as cross-linking agent and dimethyl benzyl amine (DMBA) as catalyst, were cured isothermally at 160 °C, and the progress of the reactions was followed by both thermal analysis (differential scanning calorimetry and thermogravimetric analysis [TGA]) and infrared spectroscopy (Fourier transform near-infrared and attenuated total reflection). The curing reactions were found to be approximately first order for both heat of reaction associated with cross-linking and the disappearance of the epoxy groups, even though the reduction of epoxy group concentration was found to be substantially greater than the amount expected from reactions with the anhydride, because of the formation of large quantities of vicinal OH groups. The TGA data have indicated that the pregelled mixes undergo more extensive anaerobic degradation at higher temperatures than the un–cross-linked elastomer, which is accelerated by the presence of the DMBA catalyst.

Copyright: 2015
<sc>Fig. 1</sc> .
Fig. 1 .

Structure of the main components of the mixes and expected reaction products. Left: Structure of reactants. Right: Structure of expected products.

<sc>Fig</sc> . 2.
Fig . 2.

FT-NIR spectra for the catalyzed ENR50/DDSA mix (absorbance normalized for the sample thickness). The blue trace corresponds to the pretreated sample (8 min at 160 °C) and the black trace is for the same systems cured for 50 min at 160 °C. The insets highlight the relevant wave number ranges of the spectra after isothermal cure periods, respectively: 0, 15, 30, and 50 min.

<sc>Fig. 3</sc> .
Fig. 3 .

FTIR spectra of ENR50/DDSA mix, catalyzed with DMBA, collected at different cure times up to 60 min. The downward red arrow relates to the increase in cure time to a maximum of 60 min.

<sc>Fig</sc> . 4.
Fig . 4.

Degree of conversion, αepoxy, as function of cure time for ENR50/DDSA mixes and the effect of the DMBA catalyst.

<sc>Fig</sc> . 5.
Fig . 5.

Conversion of epoxy groups during isothermal cure at 160 °C presented as a first-order process.

<sc>Fig</sc> . 6.
Fig . 6.

DSC thermograms at different heating rates for DMBA catalyzed ENR50/DDSA mixes.

<sc>Fig</sc> . 7.
Fig . 7.

DSC thermograms for scan at 5 °C on DMBA-catalyzed systems after thermal isotherms at 160 °C for periods up to 40 min.

<sc>Fig</sc> . 8.
Fig . 8.

DSC thermograms for the original sample and after 30 min cure at 160 °C. Top: Original ENR50. Bottom: ENR50/DMBA systems mixed at 160 °C for 20 min.

<sc>Fig</sc> . 9.
Fig . 9.

Example of the procedure used to estimate the residual heat of reaction using a presumed base line separating the main reactions from the secondary reactions at higher temperature.

<sc>Fig</sc> . 10.
Fig . 10.

Plots of log(ΔHr) and log(1 − α) against time, for samples cured at 160 °C up to 30 min. Top: Scan 2 °C/min up to 250 °C. Bottom: Scan 10 °C/min up to 250 °C.

<sc>Fig</sc> . 11.
Fig . 11.

TGA thermograms in nitrogen at 5 °C/ min for control samples ENR50 and ENR50+DMBA. Left axis: Weight loss with increasing temperature. Right axis: Rate of weight loss with increasing temperature.

<sc>Fig</sc> . 12.
Fig . 12.

TGA Thermograms in nitrogen at 5 °C/ min for mixes ENR50/DDSA (with and without DMBA). Left axis: Weight loss with increasing temperature. Right axis: Rate of weight loss with increasing temperature.

Contributor Notes

*Corresponding author. Email: L.Mascia@lboro.ac.uk
Received: 01 Mar 2015
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