EFFECT OF BIOLOGICAL MEDIA ON PHYSICOMECKANICAL PROPERTIES OF PVC MATERIALS* UDC 611.08:539.3

G. G. Bochkareva and Yu. V. Ovchinnikov

Research into the effects of biological media on polymer materials is being pursued in two seemingly opposite directions. Thus, while efforts are being made to develop materials that will resist the action of biological media, research is also being directed toward obtaining biodegradable products. The resistant materials are intended for use in the biochemical industry, in certain branches of agriculture, in tropical conditions, and in medicine, for prostheses compatible with living tissue [I]. The research on biodegradables is motivated by concern for the environment [2]. In all these cases it is necessary to investigate the degradation mechanism and, in particular, the mode of action of microorganisms. We have studied the effect of microorganisms on the common plastic PVC. Exposure to bacteria and mold fungi affects both the appearance the physicomechanical properties of PVC articles [3]. The extent of the changes depends mainly on the nature of the ingredients of the PVC material. The PVC itself is resistant to many microorganisms, which presents a problem from the standpoint of waste disposal [2]. It is the p!asticizers usually present in high conqentrations in PVC compositions that are mainly vulnerable to microorganimn attack. As a result of the degradation of the plasticizer and the liberation of various products of the microorganism metabolism, most PVC articles undergo a change in physicomechanical properties. In this connection, we have investigated such properties of PVC as the tensile breaking stress, the 100% elongation stress, the relative elongation at break, shrinkage, the Clash-- Berg freeze resistance, and the dielectric and optical characteristics. In Fig. 1 we have plotted the tensile breaking stress, the 190% elongation stress, the relative elongation at break and the bulk and surface resistivities of PVC film against the duration of exposure to a mold fungus medium [the film was plasticized with dioctyl sebacate, tests conducted in accordance with All-Union State Standard (GOST) 13410-67]. The curves in Fig. 2 represent the temperature dependence of the Clash--Berg modulus. From these data it is clear that the breaking stress and the 109% elongation stress increase, whereas the relative elongation at break decreases, as a result of the action of the molds. In this case the Clash-- Berg curves are shifted into the high-temperature region, and the Clash-- Berg freeze I

~;~ kgf/cm2

¢%t ¢,00 360

200

320

¢

b

280

f20

2#0 5 0

72

t68

2~

0

rs

6

~2

1,5

fO

30

Fig. I. Physicomechanlcal properties of PVC film as a function of the period of exposure to mold fungi, a: I) tensile breaking stress; 2) 100% elongation stress; 3) relative elongation at break, b: !) bulk resistivity; 2) surface resistivity. *Paper presented at the Third All-Union Conference on Polymer Mechanics, Riga (1976). Translated from Mekhanika Polimerov, No. 6, pp. 1117-1119, November-December, 1977. Original article submitted August 18, 1976. 0032-390X/77/1306-~937507.50

© 1978 Plenum Publishing Corporation

937

E, kgf/cm z

fO00~\ k \\

oo,

.%\ ,

,

-6o

.~o

-~o

-3o

? r°q -2o

-to

o

~o

Fig. 2. Clash--Berg modulus of PVC film as a function of temperature: I) film plasticized with dioctyl phthalate, starting; 2) after exposure to mold fungi; 3) film plasticized with DOS, starting; 4) after exposure to mold fungi. O,.rel. units

40 3 ,Y. rel. units

3 ' ~0

"

I

,

, ~00

~

,

,

~ ~_Jl,.~ ~00

f O00 "

" ~ l , p l

.......

500

500

Fig. 3. Change in the optical characteristics of PVC film after exposure to mold fungi: a) integral optical reflection density; b) relative luminescence, i) PVC film plasticized with DOP, DOS, starting; 2) film with DOP after exposure to mold fungi; 3) film with DOS after exposure to mold fungi. resistance (temperature corresponding to the modulus 5366) decreases. All these data indicate that the film becomes less elastic as the plasticizer is consumed by the molds. It is clear from Fig. ib that when the molds were introduced (on the 15th day) only the surface resistivity fell, the bulk resistivity continuing unchanged. Hence the attack on the material begins at the surface. Owing to the considerable loss of plasticizer (up to 30% by weight) from film containing sebacates and adipates (good sources of carbon for molds) the film shrinks appreciably, in some cases by up to 15-20% of the length. However, if the plasticizer is not a food source for the microorganisms (e.g., phosphates and phthalates), then the physicomeehanical properties of the PVCmaterial may be affected by the products of the vital activity of the microorganisms liberated at secondary sources of carbon. In these circumstances the opposite picture is observed. As the film absorbs these byproducts, which may develop, for example, in the presence of sucrose, it becomes more elastic (Fig. 2, curves I, 2). The damage suffered by PVC materials containing various plasticizers can be estimated from the change in the optical properties of samples. Film containing adipates or sebacates may change color as a result of absorbing organic pigments released by the molds. In Fig. 3 the curves represent the integral optical reflection density and the relative luminescence of PVC film of varying composition before and

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after exposure to mold fungi.* material most affected.

These data show that the film containing sebacates is the

Thus, we found that when PVC film plasticized with sebacates or adipates is exposed to the action of mold fungi, the tensile breaking stress and the 100% elongation stress increase; correspondingly, there is a decrease in the relative elongation at break and the Clash-- Berg freeze resistance, the Clash-- Berg curves being shifted toward higher temperatures. Significant changes are observed in the integral optical reflection density and the relative luminescence. On the other hand, PVC film containing phthalates may experience an increase in elasticity as a result of the absorption of products of the vital activity of the molds developing on secondary nutrient sources. LITERATURE CITED !. 2. 3.

R . K . Kulkarni, "Brief review of biochemical degradation of polymers," Polym. Eng. Sci.~ ~, No. 4, 227-230 (1965). I . R . Crowder, Meeting Reports. Plast. Polym., 42, No. 158, 53-62 (1974). R. Blagnik and V. Zanova, Microbiological Corrosion [in Russian], Moscow--Leningrad (1965).

*A. A. ll'ina participated in these experiments.

ASSEMBLY FOR STRENGTH-TESTING RINGS OF COMPOSITE MATERIALS IN ONE-SIDED HEATING V. A. Leont'ev, B.' D. Oleinik, V. G. Perevozchikov, and Yu. V. Sokolkin

UDC 620.17:678.067.5

The development of methods for mechanical testing of nonmetallic materials under nonuniform heating has great importance at present [1-3]. In the work at hand we giwa a description of the construction of an assembly for strength-testing of annular specimens of composite materials in loading with internal pressure under conditions of fast external heating. The assembly, whose scheme is shown in Fig. i, is mounted on the base 1 with a cylindrical lug. A heating element 4 in the form of a nichrome spiral is placed on the plasterof-paris insulation 2 of the base around the annular specimen to be tested 3. To reduce heat loss, a shield 5 of asbestos cord and a reflector are provided. A cap 7 is fastened to the base of the assembly with the aid of bolts 6. Between them is the working body-shaped ring 8, made from SKU-7L high-elasticity polyurethane. We note that the fabrication of the shaped ring is performed by casting into a form. Insert 9 serves to transmit force from the testing machine clamp to the shaped ring. Protective pins i0 of the base protect the spiral from shocks at the moment of specimen failure. To measure radial displacements of the specimen, four dial-type indicators Ii are fastened on the base. Thermocouple 12, which is inserted in a hole in cap 7, serves to record the temperature on the outer surface of the specimen. TABLE i.

Results of Tests of Annular Specimens

Testmethod Semidisk method Elastic-ring method

Number of Mean valueof Mean-square Coefficient of variation, specimens stress,deskgr.mm tructivet/ z deviation, kgf/cmZ

i0 10

158,6

158,0

10,2 11,9

%

6,4 7,6

Translated from Mekhanika Polimerov, No. 6, pp. 1119-1121, November-December, 1977. Original article submitted October 7, 1976.

0032-39OX/77/1306-0939507.50

© 1978 Plenum Publishing Corporation

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