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Anomalous freezing point depression of swollen gels
Author(s) -
Boonstra B. B.,
Heckman F. A.,
Taylor G. L.
Publication year - 1968
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1968.070120201
Subject(s) - crystallite , carbon black , natural rubber , benzene , materials science , composite material , chemistry , organic chemistry , metallurgy
The anomalous freezing point depression, Δ T , of benzene‐swollen vulcanizates has previously been attributed to the limitation of (benzene) crystallite size by the polymer network. This study was initiated to determine the benzene crystallite size in a number of rubber and benzene systems. A special low‐temperature specimen holder was designed and constructed in the Cambridge Laboratories for running diffraction patterns at temperatures near −30°C. X‐ray line broadening techniques were used to study a series of filled and unfilled vulcanizates of varying crosslink density. The results indicate that crystallite size is not depressed to the degree predicted by freezing‐point measurements. Benzene crystallite sizes were similar in all rubber benzene systems, regardless of degree of crosslinking or benzene fraction, although carbon black loading appears to increase crystallite size. This effect may be attributed to lesser depth of penetration of the x‐rays due to greater density as carbon black loading increases. Additional studies measuring the Δ T for solutions and similar vulcanizates of NR and SBR over a wide range of rubber concentrations showed that at the same rubber in benzene fraction, crosslinking increases Δ T but the addition of carbon black reduces Δ T . An explanation for the observed phenomena is advanced.