The paper chromatographic behaviour of the following antioxidants has been investigated.
A. Aldol-α-naphthylamine (M. P. 65100°C)
C. Aldol-α-naphthylamine (M. P. 140°C min)
P. A. Phenyl-α-naphthylamine
D. Phenyl-β-naphthylarnine
F. Di-β-naphthyl-p-phenylenediamine
H. N, N'-diphenyl-p-phenylenediamine
Agerire Stalite Mixture of mono and di-hepthlated diphenylamine
Agrite Resin D. Polymerized trimethyl-dihydroquinoline
Santoflex B. 1.2. -dihydro-2, 2, 4-trimethyl-6 phenylquinoline
Santoflex BX Blend of Santoflex B (85) +H (15).
After antioxidants (dissolved in acetone) were coupled with diazonium salt of aniline, reaction products were developed on paper strip (Toyo paper strip for Chromatography No.50) up to about 30 cm high. and then, after drying at room temperature, paper strip was treated with conc HCI vapor in order to observe developing spots having Specific colour.
As developers a number of solvents and solvent mixtures were investigated.
Acetone-benzene-water (61 : 4 : 35 by volume at 20°C) -was finally chosen as a best developer for separation and identification of antioxidants.
The following paper chromatographic data were obtained on antioxidants alone. (Table 1)
Table 1.
Paper chromatographic data of various an-tioxidants (developed at 20°C)
Developer. Aceton-Benzene-Water
61 - 4 - 35
(by volume at 20°C)
Antioxiodants R_f × 100 Specific Colour of Spot
A 90, 78 Reddish Violet
C 90, 78 Reddish Violet
P A 61 Bluish Violet
D 48 Orange
F 98100 Pinkpale orange
H 98100 Pinkpale brown
Agerite stalite 37 (5052) Violet
Santoflex B 49 Pink
Agerite Resin D. 060 Pale Pink diffuse zone
(a) A and C showed over laped spot.
(b) H and F also showed oved laped spot
(c) Agerite Resin D gave diffuse zone.
(d) D and Santoflex B mutually interfered.
With the above chromatographic deta as a guide, further experiment was carried out in order to detect and identify of antioxidants which are present in mixed state. It was possible to separate and identify component antioxidant in A+PA+D, A+H+PA, F+Agerite resin D, C+D, F +Agedite stalite etc,
Therefore, it would be expected that the proposed method provides a very convenient means for identification of antioxidant mixture. when A and C or H and F. or D and Santoflex B are not present together with in the mixture.
Based on the results obtained on above-mentioned experiments, the identification of antioxidants was carried out with tread mix accelerated with MBT and tube mix accelerated with MBTS.
Vulcanized Rubber (5 g) grinded by passing through rolls was extracted with acetone (10 cc) at room temp. and acetone extract was evaporated to 2cc, then it was treated by the some method as antioxidants in acetone were treated.
The chromatographic treatment has been successfully applied to the vulcanized rubber. Chromatographic data obtained were quite similar to the data of antioxidants in free state.
The only exception was Santoflex B which was not detected.
Paper chromatographic method proposed in this experiments could be applied successfully to the identification of antioxidants either alone or in vulcanized rubber accelerated with MBT and MBTS. But more precise and general method could be developed by finding diazonium salt and developer which gives more specific spot and colour than diazonium salt of aniline and developer proposed in this experiment does.

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The flex-cracking appears on the surface of vulcanized rubber subjected to repeated, local elongation. The authors considered the boundary between rubber hydrocarbon and fillers (or every particle) as the nucleus of cracking.
They examined the test pieces of vulcanized rubber compounded with ZnO, CaCO₃ “Haku enka”, basic MgCO₃, clay, mica powder respectively by the De Mattia flexing machine, measuring the times of flexing, at which pin holes appear and cracks grow to 1 mm in length, and the rate of crack growth.
They recognized that the above results had close relation with the rate of cavity formation which had been given in the last report.
The greater the rate of cavity formation, the smaller the resistance against flex-cracking.

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Another verification, with regard to the recent development of the theory which has been described in the preceding papers on the assertion that the essential distribution of tensile strength of rubber is correctly of doubly exponential type is attempted in the present paper by use of four kinds of experiments whose details were previously published. Being concerned with the order statistics themselves, this verification is carried out as follows : the observed expectations and standard deviations of n order statistics which are computed practically from the experimental values when n=3, 4 and 5 are compared with the theoretically estimated expectations and standard deviations, respectively.
The comparison comes to the conclusion that all the expectations computed experimentally and theoretically are very well agreed although the relatively poorer agreements are seen between the practical and theoretical standard deviations.

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