.
10 I I 12
13 14
16 17
15 18
Figur« 2. Su n ligh t and O z o n e R eilttance o f H y e a r - G c o n M ixtu re»
MJxt Hycar Geon,
No. OR, % %
1,10 100
4,13 75 25
7,16 50 50
M lxt Hycar G«on, M ixt Hycar Gaon,
No. OR, % % No. OR, % %
2,11 90 10 3,12 80 20
5, 14 70 30 6,15 60 40
«»17 25 75 9,18 100
The cold milling properties of the mixtures improve in direct proportion to the Hycar OR concentration; conversely, the hot mill
ing properties are improved with Geon ad
dition. A good balance is obtained with ap
proximately 20-40% Geon.
Precautions must be exercised in compound
ing mixtures of Hycar OR and plasticized Geon. Excessive use of most metallic oxides and salts and of amine-type age resisters and accelerators should be avoided. At elevated temperatures such materials tend to catalyze breakdown of polyvinyl chloride resins and thus liberate hydrochloric acid. (Salts and oxides of lead, however, act as stabilizers for polyvinyl chloride.)
Sulfur, accelerator (benzothiazyl disulfide, mercaptobenzothiazole, etc.), and activator (litharge in this case) are used approximately in proportion to the Hycar OR in the mixture.
The use of softeners and pigments may be varied in the same manner as in Hycar OR (12, 16) to obtain the desired physical prop
erties. The 3 % age resister already present in Hycar OR plus the inherently good age- resisting qualities of Geon 102 should be suffi
cient protection for almost all uses. Fatty acids aid both in processing and in obtain
ing the optimum in physical properties.
The curing rates of the mixtures are similar to those of Hycar OR. The curing curves become progressively flatter with Geon addi
tion. Cured articles, in which 25% or more Hycar OR is present, may be removed from the mold while hot. This represents an ad
vantage over molded vinyl chloride resins
(1 0 0% ) which generally must be cooled in the
press before removal.
C O M P O U N D S OF 75% HYCAR OR-15 WITH S5 % G E O N 10i
The preliminary studies of the previous section showed that a favorable balance be
tween the sunlight, ozone, and aromatic sol
vent resistance of Geon 102 and the thermo
setting properties of Hycar OR was obtained with a mixture of 75% Hycar OR-15 and 25 % Geon. With this polymer combination as a basis, the mixture (Table II) was prepared upon which a complete compounding study was made.
The mixtures were prepared by. milling well-masticated Hycar OR-15 into plasticized Geon at 220° F. Compounding was based on 125 parts of the mixture (Table II). Batches were mixed at 120-160° F. on a 12-inch mill.
The compounds were cured at 300° F., and optimum cures were determined from stress- strain data. Physical tests were run as follows:
S t r e s s - S t r a i n . A.S.T.M. p r o c e d u r e (S).
H a r d n e s s . Shore durometer, type A
(tested on Vr-inch sheets at room tempera
ture and 212° F.).
R e b o u n d . Schopper method, tested on Vi- inch sheets at room temperature and 212° F.
C o m p r e s s i o n S e t . A.S.T.M. p r o c e d u r e , m e t h o d s A a n d B (2), t e s t e d o n p e l l e t s ' / » i n c h t h i c k a n d 1.129 i n c h i n d i a m e t e r .
I m m e r s i o n T e s t s . A.S.T.M. procedure-»
m e t h o d B (11).
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734 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 36, No. 8
146.0 138.0 168.6 109.7 314 238 211 212 157. 1
3 6 .8 2 1.3 33.1 15.8 52.1 33.1 2G 3. 0 - 2 2 . 6 prior to testing; the longitudinal and transverse tear values were averaged.
H y s t e r e s i s . Goodrich flexometer (15), tested at room tem
perature and 212° F. with 17.5% stroke and 55-pound load.
A c c e l e r a t e d A g i n g S t r e s s - S t r a i n . T w o p r o c e d u r e s w e r e
The more important physical properties of these compounds are shown in Figure 3 and Tables IV, V, and VI.
The mixture shows advantages over Hycar OR-15 in resistance to sunlight and ozone (Figure 2), tear (Figure 3, g), flex cracking (Table V), and aging (Figure 3, 6 and c). It also has improved resistance to swelling in benzene and carbon tetrachloride (Table VI) and slightly higher plasticities (Table IV).
The mixture gives lower tensile strength (400-800 pounds per square inch), 300% modulus, and elongation than Hycar
OR-15 in comparable compounds (Figure 3, a). Because of the somewhat thermoplastic nature of the mixture, it manifests a greater decrease in hardness and a proportionally greater increase in rebound (Figure 3, d and e) than Hycar OR-15 at elevated tempera
tures. Compression set for the mixture is higher than Hycar OR-15, particularly in compounds tested:
under constant deflection (Figure 3 ,/) .
Hycar OR-15 shows better abrasion resistance than the mixture which, in turn, has better abrasion resistance than natural rubber (Figure 3, h). The hysteresis values of the mixture are high (Figure 3, i ) .
M i x i n g a n d C o m p o u n d i n g . The mixture of 75 % Hycar OR-15 and 25% Geon 102 (Table II) is slightly tougher than Hycar OR-15 on the mill but quickly --- breaks down to give a processable rubber which is less
sensitive to temperature change. Considerable heat is generated during breakdown and mixing. For best milling it is advisable to keep the mill temperatures between 120° and 160° F.
Tubing, calendering, and molding operations may bo carried out on rubber processing equipment. Because the mixture has less nerve than Hycar OR-15, it is possible to extrude or calender to much narrower gage limits. In molding, the stock should be used as fresh as possible and, if practical, resinous type softeners should be included in the compound to avoid flow and fusion cracks.
In compounding the mixture of Hycar OR-15 and Geon 102, zinc oxide (5 parts) was used for activation without harmful effect. This activation was less scorchy and gave vulcanizates with somewhat better physical properties than --- similar compounds activated with litharge. For ex
treme heat service, however, it is advisable to sub
stitute 2-3 parts of litharge for the zinc oxide to stabilize the polyvinyl chloride.
The preferred sulfur-accelerator ratios for general compounding are 1.2 parts of each per 125 parts of the mixture (Table II). Modifications of these ratios may be necessary for special compounds. Vulcan
izates with good physical properties, particularly after aging, may be obtained with a cure employing tetramethylthiuram disulfide (3 parts) and mer- _ _ _ _ _ captobenzothiazole (3 parts). High-quality hard rubber products may be obtained with 35-40 parts of sulfur.
The use of the remaining compounding ingredients (softeners, pigments, etc.) in the mixture (Table II) have been dealt with in the previous section. By proper selection of softeners and pigments and by control of the cure, practically all of the pos
sible varieties of compounds with Hycar OR-15 can be made with this mixture