Behavior of Polyvinyl Chloride Plastics under Stress J
J
J. J. RUSSELL General Electric Company, Schenectady, N. Y.
The procedure used to determine the tensile s tress-strain diagrams for polyvinyl chloride plastics over a temperature range of -50" to +80° C. is described. For compounds containing little or no filler, Poisson's ratio is about 0.5. This value is practically the same as that obtained for soft vulcanized rubber. The stress-strain curves change in shape as the temperature is lowered and ultimately reduce to the "brittle point". This temperature is characteristic for each composition of plasticized polyvinyl chloride. The stress V S . temperature plot consists of at least two portions-a low-er temperature portion exhibiting a linear relation between stress and temperature, and a higher temperature portion following an exponential relation. The heats of activation thus derived are of the same order of magnitude as those obtained for a number of pure metals. O L W I K Y L chloride alone can be molded at and above 120" C. under a pressure of 35.19 kg. per sq. cm. (500 pounds per square inch), but the resulting product is very hard at room temperature. To reduce or eliminate this brittleness, it is necessary to mix another substance, known as a plasticizer, with the polyvinyl chloride. When the two in proper proportions are milled together a t 105-115' C. on rubber compounding rolls, a pliable, rubberlike material is formed. Even these materials, however, tend to become brittle enough to be readily broken a t some definite l o r temperature (the "brittle point"), Stress-strain diagrams and brittle points for polyvinyl chloride plastics with different plasticizers have been oLtained and are given here.
P
WIRE ISSULATED WITH FLAMEXOL (PLASTICIZED POLYVINYL CHLORIDE) Is FLEXIBLE
pressed into sheets 34.29 X 16.51 X 0.10 em. (13.5 X 6.5 X 0.040 inch) in a flash-type mold at 150" C. for 3 niinutes under 38.7 kg. per sq. cm. (550 pounds per square inch) pressure. The sheet was usually quite uniform, was transparent unless fillers had been added, and was tested only if it was free from imperfections. The test specimen, a dumbbell of the size and shape described by the A. S. T. M. (I), was cut from this sheet of plastic, placed in the grips, and adjusted so that the tension would be as uniform as possible. The stretching was performed at a constant rate of 14.48 cm. (5.7 inches) per minute, during n-hich time the load and elongation were recorded by a .park recorder at increments of 25 per cent elongation. Six plasticized polyvinyl chloride compounds were chosen to illustrate the data obtained in this work, although many other compounds and mixturei; of compounds can be used as plastirizers. The compositions of these plaitics are given in Table I.
Preparation of Samples and 31ethod of Testing A Srott tester, model LP, was fitted with an air thermostat capable of maintaining a uniform temperature to *0.5' C. over a range from 30" to 150" C. By the use of liquid nitrogen and solid carbon dioxide, temperatures as low as -50" 0. could be obtained constant t o A1.0' c'. A standard technique was employed for the preparation of the test pieces. Three hundred grams of the plastic \yere made by mixing the Plasticizer and the polyvinyl chloride (gamma form) until a uniform mixture was obtained. (In compound 6, 2 er cent of chrome green was included as an inactive filler.) htlling was carried out on differential compounding rolls for 10 minutes at 100" to 110" C. with the rollers set about 0.015 em. (6 mils) apart. The compound was
WIRE IXSULATED WITH FLAJIEXOL (PLISTICIZED 1 ' 0 ~ 3 VINYL cHI.ORIDE) HAS
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VOL. 32, NO. 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Chloroform Extract of Reclaimed Rubber T
H E purpose of this paper is to discuss the effects of the processing operations in the manufacture of reclaimed rubber which may affect its solubility in chloroform and also the significance of the chloroform extract in interpreting the quality and processibility of reclaimed rubber. The amount of chloroform extract appears to be significant when an examination is made of reclaimed rubber after acetone and chloroform extractions have been made. The residue after extraction is hard and elastic, and on a mill it resembles vulcanized rubber. Obviously, the joint plasticizing action of the extractable plasticizers, which appear chiefly in the acetone extract, and depolymerized rubber, which is the chief constituent of the chloroform extract (17, 18), makes possible the production of commercial reclaimed rubber. A number of factors which contribute to the degree of formation of chloroform-extractable material are discussed in this report. The significance of chloroform extract has been mentioned or discussed by several investigators ( 3 , 7-13, 15-19). Stafford (16)called attention in 1926 to the presence of the chloroform-soluble portion of reclaimed rubber and also demonstrated that the chloroform-soluble rubber contained a definitely lower proportion of combired sulfur than remained in the chloroform-insolubleportion.
HENRY F. PALMER AND F. L. KILBOURNE, JR. Xg-10s Rubber Company, Akron, Ohio
Weber (17) described the chloroform extract and pointed out the low viscosity of its solution as evidence of a Iarge degree of depolymerization or disaggregation. He pointed out that the amount of chloroform extract did not give an accurate indication of the difference in plasticity between various reclaims. Winkelmann (18) showed four cases where the chloroformsoluble portion of the reclaimed rubber was from 37 to 45 per cent of the total rubber hydrocarbon of the reclaim and yet this portion contained less than 10 per cent of the combined sulfur. He offered two possible explanations: (a) The chloroform-soluble rubber is rubber that was merely aggregated in the presence of, but not combined with, sulfur during vulcanization; (b) the chloroform extract consists of fragments of long rubber molecules which were combined with sulfur a t one end of the molecule during vulcanization and which were broken off during the devulcanization. Boiry (3) showed that substantially all of the chloroform extract is produced in the early part of the devulcanization
