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T H E JOURNAL OF INDUSTRIAL A N D ENGTNEERING CHEMISTRY
Vol. 14, No. 9
Physics of Rubber, 1920-1921 By W. B. Wiegand MANAGING DIRECTOR, AMES HOLDGN MCCREADY, LTD., MONTREAL, CANADA
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ERHAPS the most valuable publication of the period is “Plantation Rubber and the Testing of Rubber,” by G. S. Whitby; Part I1 of which includes a review of the work on rubber by some of the master physicists of the nineteenth century. Kothing could be more fruitful than the repetition of much of this work, with with due regard to composition and life history of the mixings employed.
peated stresses, emphasizing the superiority of high-rubber compounds for work (such as in airplanes) requiring a slow rate of energy absorption. An important application to automotive equipment is the use of rubber sprillg shackles.16 Hysteresis losses, as influenced by cure, pigment loading, and cyclic elongation, are described by Wiegand.16 An interesting fact is the very large increase in resilience induced by the addi-. tion of a highly dispersed nonelastic phase PHYSICAL STRUCTURE such as carbon black. ’ UNSTRAIKED-The spatial distribution VOLUME CHANGES-The outstanding of discrete ingredients in vulcanized rubcontribution is H. F. Schippel’s4 paper ber has been admirably studied by Mr. H. showing the enormous increases in volume Green,lI* whose photomicrographs show (as much as 100 per cent) when highly clearly the phenomena of dispersion and pigmented stocks are strained. This has agglomeration. The extension of his work a vital bearing on elastic theory. Santo uncompounded rubber may add to our derson’7 has studied the thermal expansion knowledge of its ultimate colloidal strucof various mixings, finding no discontinuity ture and so supply visual confirmation or at the vulcanizing point. otherwise of the net work hypothesis of GRAIK-van Rossem18 has described C . 0. North,2 and of the spheroidal theory calender grain, including its dirappearance of R. ’CV. L ~ n n . ~ through heating, which he assigns to the STRAINED-The development of vacuJoule effect. In this opinion he is opposed oles a t the poles of particles in strained by Wiegandlg and Lunn3 who regard the rubber, predicted on theoretical grounds phenomenon as essentially due to viscosityby H. F. S ~ h i p p e l has , ~ been visually conW B. WIEGAID temperature relationships. (S e e a 1s o firmed by H. Green.5 This phenomenon Skellon.20) has deep Fignificance in connection with the theory of reinHardness tests have been thoroughly rtudied by Gurney,21 forcement .6 particularly as applied to the manufacture of rubber-covered MECHAXICAL PROPERTIES rolls. The physical testing of rubber has been actively carried EFFECT O F COMPOUNDJxG INGREDIENTS-The connection on but .with no important contributions to testing technic.7 between fineness of subdivision and reinforcing action has’ to equipment, procedure, and represen- been definitely established.2*6 Further work is necessary Standardjzation tation is beginning to receive the attention it deserves.8 to clear up the role played by adhesional forces as distinSTREGS-STRAIN CuRvE-The attention of rubber workers guished from specific surface. The mechanical properties continues to be directed less toward breaking values and of vulcanized rubber have been shown to be controllable toward the complete curve. The “conchoid” analogy Over very wide ranges through the intelligent use Of various of schidrowitz and Go~dsboroughhas heen shown to be fillers.. The remarkable reinforcing properties of carbonate inadequate;9 and Shields,io and somewhat later, Hatschek,ii of magnesium have been well established by Greider.22 Minstudy by have published ,new formulas based on curves distorted by eral rubber has been the subject Of a c. O. North-23 the former, who seems calculation to actual cross section; to use only the early part of the curve, arriving at a cornThe important bearing of particle shape upon the phenomplex logarithmic expression, the latter deriving in elegant ena of grain, set, and hysteresis demands further OF PARTICLE SIzE-The importance of subMEASUREMENT fashion a rectangular hyperbola for the same curve. The prerent writer finds that when the Hatschek method is ap- diviqion as a guide to pigment reinforcement has stimulated plied t o curves for stocks representing a range of typical H. Greenz5to develop to great precision the direct microfactory mixings the construction is inapplicable. More- scopic method. Using violet light, this worker has been able over, neither author has established any physical significance to measure particles down to 0.2 micron in diameter. H. for the parameters that appear in their equations. A. Gardner26 has described a very novel method of estiVogt12has described a modified method of recording stress- mating the fineness and texture of pigments by rubbing them strain data, which facilitates the closer study of reversion on a phonograph record. W. W. VogtZ7favors the obscurphenomena. ometer method of measuring average particle size. This has ENERGY RELATIONSHIPS-of the many physical constants had strong criticism from the standpoint of refractive index.28 Those who favor clay as a compounding ingredient will used to described the properties of a sample, perhaps the most comprehensive single index is the energy of resilience find the paper by Comberz9very suggestive. as measured by the area subtended by the 8.-s. curve on the The race for superfine rubber pigments has led to intenelongation axis. Proposed in June 1920,13 this quantity sive research, working both from the atomic state (sublimed has been widely adopted. Gurney and TavenerI4 describe litharge, zinc oxide, magnesium carbonate), and from the the energy absorption of various mixings subjected to re- coarse condition.30 Thus we may soon come upon the ideal pigment, one * Numbers in tevt refer to References at end of paper.
