Compressibility of natural and synthetic high polymers at high pressures

Abstract

Co mpressio n da ta ( -t. V IVo) are repor ted between 1,000 a nd 10,000 atmos pheres for the foll owing materi a ls : dry cellulose, polyvinylidene chloride (Saran), polyeth ylene, polyrn onochlorotrifluoroeth ylene (K el-F) , polytetrafluoro ethy le ne (T efion ), a polyester (Seleetron 5003), and raw r ubbers, H ycar OR25, H ycar ORIS, Neoprene, a nd Thiokol ST . All compression curves are smooth excep t that for polytetrafiuoroethylene, which shows a transition at 5,500 a t mospheres, resulting in a change in volume (t. V I Vo) of approximatel y 2 percent. Coefficients of t he cubic eq uat ions, -t. V I Vo= a (P -2000) + b (P -2000)2 +C (P -2000)3 fi tted to t he data are as follows: Cellulose: a = 9.26 X 10-6 , b=-3.25 X 10-1O, c= 2.93 X 10-'s; polyvinyJidene chloride (Saran) : a = 2.17 X 10-s, b=-1. 90 X IO-9, c= 8. 73 X lO-l4 ; polyethylene: a = 1.89 X IO-s, b=-1.45 X IO-9, c = 6. lO X lO-14 ; polymonochlorotrifjuoroethylene (Kel-F): a = 9.89 X lO-6, b=-4. 74 X lO-1O , c= 8.29 X lO-' 5 ; pol yester (Selectroll 5003) : a = 1.76 X lO-s, b=-1.23 X 10-9, c= 4.82 X lO-14 ; H ycar OR25: a = 2.26 X IO-5, b= -2.03 X lO-9, c= 9. 09 X IO-I4 ; H ycar OR15: a = 2.17 X 10-5, b=-2.03 X lO-9, c = 9.42 X IO-I4; Neoprene: a = 2.04 X IO-s, b=-1.75 X 10-9 , c= 7.66 X 10-14 ; Thiokol ST : a = 1.92 X 10-5, b= -1.41 X 10-9, c= 6.07 X 10-14 • Co mprcssibilities calculated from these eq uations s how fictitious minima cir ca 10,000 atmosphere, although t he eq uations represen t the data satisfacto ril y to 10,000 atmospheres. The data given co mpare favorably with those obtaine d 0 11 similar materials by previou workers.

The Effect of Pressure on the Mechanical Properties of Polymers

“…Equation (19), which is discussed in the results section, was used to correct the initial cross-sectional area of the specimen to the area existing at the experimental temperature and pressure, Since the extension of the specimen requires a finite time, tl, initial portions of the response, covering a time interval of about 10t l to 25tl, were discarded.…”

“…We took the effect of pressure into account by considering that poOlP = V!VOO where V is the volume at temperature T and pressure P and Voo is the volume in the reference state, and applying the Murnaghan equation (19) to obtain the volume at pressure P. Sharda and Tschocgl" ' have recently shown that POD! P should be replaced by (V !VOO)-~, where l' is a material parameter whose value is 0.2 for natural rubber.…”

Thermodynamic properties of high polymers as a function of their pretreatment as determined by specific heat measurements

“…By differentiating [ll] and [13] it is possible to obtain equations for Owc/dT which enable us to calculate (29) the effect on the specific heat of a change of equilibrium crystallinity with temperature. [17] As mentioned above the assumption has been made in the derivation of these equations that as and 2 Hu are independent of T and XA.…”

“…[5] 5 2 cp --cv = VT ~- [5] where V is the specific volume, ~ the cubical coefficient of thermal expansion and fl the compressibility, it is possible to calculate the difference between Cv and Co for those polymers whose compressibility has been measured. Weir (13) has measured the compressibility of a low density polyethylene at high pressures, above 1000 arm., see also (12), but it is the compressibility at atmospheric pressure that should be used in Eq. [5].…”

“…where p is the probability that an A-group is succeeded by another A-group (taken as the same as X~ in a random copolymer), O is a function of the temperature, 0 = (A Hu/B) (1IT-1/Tin 0) [12] and ~*, the smallest length of crystallites existing at equilibrium at T, [13] where D can be calculated from the expression D = ~xp (--2 ~s/R T).…”