COMECON
DIARY
SYMPOSIUM
ON R A D I A T I O N - M O D I F I E D
L . S. A k t a b a e v a , V.M. a n d l~. I . S e m e n e n k o
POLYMER
MATERIALS
Kodyukov,
This s y m p o s i u m of s p e c i a l i s t s f r o m COMECON m e m b e r - c o u n t r i e s and Y u g o s l a v i a was held Sept. 13-16, 1977, in W a r s a w . The p a p e r s dealt with the m a i n lines of advance in applied radiation c h e m i s t r y and s u r v e y e d the accumulated data on the p r a c t i c a l use of radiation modification of p o l y m e r s and r a d i a t i o n - c h e m i s t r y gene r a l l y in the industries of COMECON m e m b e r - c o u n t r i e s . T h e r e w e r e altogether 58 p a p e r s at the p l e n a r y s e s s i o n s and t h r e e sections: radioation p o l y m e r i z a t i o n and crosslinking, p r o c e s s e s in radiation grafting, and technology and equipment. The r e s e a r c h e s in hand in COMECON m e m b e r - c o u n t r i e s c o r r e s p o n d in scope and scientific level to world t r e n d s in the development of radiation technology and engineering. Radiation-modified p o l y m e r s have now been used on an industrial scale for :[5 y e a r s ; the advantages of radiation techniques a r e obvious, p a r t i c u l a r l y in the low t e m p e r a t u r e and p r e s s u r e s at which the p r o c e s s e s c a n be operated, t o g e t h e r with the v e r y high yields of the d e s i r e d product, which goes with high purity and s c o p e for close control. In addition, the c o s t s of the modification are low when high-power e l e c t r o n a c c e l e r a t o r s a r e used. The level of r e s e a r c h is such that it is possible to r a i s e the p e r f o r m a n c e of technological p e r f o r m a n c e s c o n s i d e r a b l y . I n t e r e s t h e r e is attached to s e v e r a l p a p e r s f r o m Hungary, the G e r m a n D e m o c r a t i c Republic, Poland, and the Soviet Union that dealt with the effects of s e n s i t i z e r s in radiation c r o s s - l i n k i n g , since t h e s e can r e d u c e the o p t i m u m radiation dose and thus the cost of the p r o c e s s ; other studies have been concerned with the effects of the a t m o s p h e r e used in the p r o c e s s , the s t r u c t u r e of the p o l y m e r , the p h y s i c a l s t a t e of the m a t e r i a l , the i r r a d i a t i o n t e m p e r a t u r e , and other such f a c t o r s decisive in the p r o c e s s . One of the new and p r o m i s i n g t r e n d s is the combination of ionizing radiation with e l e c t r i c fields, light, etc. A p a r t i c u l a r e x a m p l e of this combined t r e a t m e n t is c r o s s - l i n k i n g in polyethylene under illumination and i r r a d i a t i o n . Radiation-modified m a t e r i a l s are based to a considerable extent on polyethylene, PVC, and p o l y e s t e r s , and these a r e of c o n s i d e r a b l e p r a c t i c a l value in e l e c t r i c a l engineering, c h e m i c a l engineering, e l e c t r o n i c s , n u c l e a r power, and the building i~dustry. A m a j o r example of u s e s for r a d i a t i o n - m o d i f i e d p o l y m e r s is the use of radiation c r o s s - l i n k e d polyethylene as an insulator in high-voltage cables. The poor t h e r m a l stability of polyethylene has p r e v i o u s l y p r e v e n t e d its extensive use in the cable industry, but the stability i m p r o v e s on c r o s s - l i n k i n g . H e r e r a d i a t i o n - c h e m i c a l methods are of p a r t i c u l a r value. Cables with radiation c r o s s - l i n k e d polyethylene insulation can be installed in buildings, on the open ground, and even in the p r e s e n c e of u n d e r ground water; they are insensitive to m e c h a n i c a l v i b r a t i o n s and can sustain c o n s i d e r a b l e v i b r a t i o n a l loading. The expected working life at the m a x i m u m p e r m i s s i b l e field strength is 50 y e a r s o r m o r e . T h e s e f e a t u r e s of the cable insulation also m a k e the m a t e r i a l p r o m i s i n g for use in n u c l e a r power. The industrial production of high-voltage cables with this modified polyethylene has been in hand for s o m e t i m e in the G e r m a n D e m o c r a t i c Republic and the USSR. Shrinkable components f o r m one of the m a j o r f o r m s of r a d i a t i o n - m o d i f i e d product available in m o s t ind u s t r i a l l y developed countries: tubes, s l e e v e s , films, and other such shaped components. T h e s e m a t e r i a l s a r e capable o f m e e t i n g v e r y rigid specifications, such as prolonged viability at high t e m p e r a t u r e s (up to 250"C), r e tention of e l a s t i c i t y at low t e m p e r a t u r e s (down t o - 6 0 " C ) , good oil r e s i s t a n c e , v e r y high r e s i s t a n c e to s u r f a c t a n t s , excellent c o r r o s i o n r e s i s t a n c e , and r e s i s t a n c e to m o s t solvents. These good f e a t u r e s go with a combination of good p h y s i c o m e c h a n i c a l and other p r o p e r t i e s to make the m a t e r i a l s o f c o n s i d e r a b l e value in r e a c t o r engineering and o t h e r a r e a s in n u c l e a r engineering. The m a j o r lines of r e s e a r c h on new m a t e r i a l s includes the development of swelling c o m p o s i t e s based on polyolefins; such m a t e r i a l s should p r o v e of c o n s i d e r a b l e value if they can be produced successfully. An interesting s e r i e s of r e s e a r c h e s was also r e p o r t e d on radiation modification of highly filled m a t e r i a l s based on polyolefins, which can reduce substantially the consumption of the p o l y m e r while providing m a t e r i a l s T r a n s l a t e d f r o m A t o m n a y a Energiya, Vol. 44, No. 3, pp. 281-282, March, 1978.
0038-531X/78/4403-0319507.50
9 1978 Plenum Publishing C o r p o r a t i o n
319
and components with valuable properties. Large amounts of filler in polyethylene reduce the strength and the melting index, which complicates the processing technology. Radiation-modified filled polyethylene can pro~ide strength characteristics as good as those of pure polyethylene, particularly ff carbon black and SiO2 are the fillers. A valuable feature is that the improvement in the physicomechanical p a r a m e t e r s of the radiationmodified and filled polyethylene is maximal at 100-110~ and this predetermines the area of application of such materials (manufacture of pressurized tubes for hot water, and also for handling corrosive liquids, as polyethylene is highly resistant). Such materials may also find applications in the nuclear industries. The r e s e a r c h and development lines have now provided a basis for general use of radiation-chemical technology; the current level of attainment and future progress in this area have been determined to a considerable extent by the design of several types of high-current electron acceleratorsintheUSSR, which have many industrial applications (the Elektron, the ]~LV, the ILU-6, etc.), which is in addition to the design of highintensity ~,-ray sources containing 6~ and the use of irradiation loops in nuclear react ors. Electron accelerators were overwhelmingly the radiation source p r e f e r r e d in the studies reported at the symposium the reason for this is that the radiation utilization factor is much higher, while the monoenergetic radiation is readily controlled to a constant dose rate, and the cost of the radiation shielding is considerably less. Also, the latest accelerators provide outputs in the range of absorbed doses necessary for good industrial productivity, since this has to be comparable with the throughput of other polymer-processing equipment (ext r u d er s , casters, etc.), which means that the a c c e l e r a t o r can be incorporated in a production line. At the present time, studies designed to provide higher powers and cheaper accelerators are in hand along with l a r g e r - s c a l e production of existing designs, which has involved particular r e s e a r c h e s on reliability, control simplicity, servicing, and size and weight reduction. The papers presented at the symposium show the important place that this area of technology now occupies in the processing of polymers; the development prospects pose major tasks for r e s e a r c h e r s and technologists, which range from purely chemical problems to aspects associated with the design of new and better radiation systems. Advances in these areas will provide the economics of COMECON member-countries with new materials having combinations of valuable properties, particularly ones for which the demand is rising continuously.
320
