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1963 Volume 5 Issue 3
1963, 5(3): 101-109
Abstract:
Effects of vulcanizing temperature and time on the physico-mechanical properties of wet-gel and dry-film of vulcanized natural latex were studied．The physico-mechanical properties of wet-gel became worse when the temperature or the degree of vulcanization was increased．The properties of dry-film were improved by increasing the degree of vulcanization and became worse on increasing the vulcanizing temperature(while the combined sulphur is constant)．The differences in these properties between the wet-gel and dry-film were attributed to the difference in the mechanism of rupture，e.g.，inter-globule for wet-gel and intraglobule for dry-film．The effect of vulcanizing temperature was explained by the non-uniform distribution of the intraglobule sulphur-bond．in the latex．
Effects of vulcanizing temperature and time on the physico-mechanical properties of wet-gel and dry-film of vulcanized natural latex were studied．The physico-mechanical properties of wet-gel became worse when the temperature or the degree of vulcanization was increased．The properties of dry-film were improved by increasing the degree of vulcanization and became worse on increasing the vulcanizing temperature(while the combined sulphur is constant)．The differences in these properties between the wet-gel and dry-film were attributed to the difference in the mechanism of rupture，e.g.，inter-globule for wet-gel and intraglobule for dry-film．The effect of vulcanizing temperature was explained by the non-uniform distribution of the intraglobule sulphur-bond．in the latex．
1963, 5(3): 110-122
Abstract:
The properties of cis-1,4-polybutadiene rubbers with different molecular weights which were obtained with titanium catalyst have been studied．The properties of raw cis-1，4-polybutadiene rubbers with different molecular weights are similar to each other with respect to (1) gel content，less than 1％，(2) cis-1，4-con-tent,93—97％，and (3) glass temperature，-110 to一114℃ (Table 1A)．However，the Mooney viscosity increases rapidly with [n] (Fig．1)．It is shown by stress-strain curves that a11 the cis-1，4-polybutadiene samples under examination do not crystallize during stretching (Fig．2)．The behaviour of cis-1，4-polybutadiene in milling is very sensitive to temperature．Carbon black compoundings have been carried out on an open laboratory mill at cylinder temperatures of 25，40，and 60。C，respectively． Smooth compounds from which vul-canizates with tensile strength over 200 kg／cm2 may be prepared can only be obtained at 25℃． When compounding is carried out at 40 or 60℃，cis-1，4-polybutadiene tends to crumble(Fig．4)，no smooth compound can be prepared，and the vulcanizate obtained loses tensile strength(Fig．3)．According to the following experimental results： (1)no gel formation，no signi ficant degradation，and no change in microstructure can be observed when cis-1，4一poly- butadiene is masticated either at 25℃ or at 40 or 60℃ (Fig．6 and Table 3)；(2)the effect of temperature on milling is reversible (Table 4)，it is presumed that the lOSS of tensile strength of the vulcanizate obtained from compound prepared at 40 or 60℃ is due to the difficulty of incorporation and dispersion of carbon black into the cis-1,4-polybutadiene rubber at a temperature above 40℃．This presumption is supported by the microscopic photographs of the CROSS-sections of the vulcanizates(Fig．5)．It is found that the tensile strength of the vulcanizate decreases rapidly as the mo-dulus(M300％) exceeds 60 kg／cm2 (Fig．8)．However，with a suitable amount of sulphur to control the degree of cross-14nking，vulcanizates of tensile strengths over 200 kg／cm2 can be obtained (Fig．8 and Table 1B)．The elastisity (Yerzley) and abrasive resistance of cis-1，4-polybutadiene vulcanizates are much better than those of natural rubber(Table 1B)．The effect of molecular weight of cis-1,4-polybutadiene on the mechanical proper-ties of the vulcanizate has been investigated． It is found that vulcanizates of tensile strength around 200 kg／cm2 can be obtained within wide range of molecular weights ([n] 2.5 to 3.6)，whereas elasticity increases with the M of the raw rubber(Fig．9)．
The properties of cis-1,4-polybutadiene rubbers with different molecular weights which were obtained with titanium catalyst have been studied．The properties of raw cis-1，4-polybutadiene rubbers with different molecular weights are similar to each other with respect to (1) gel content，less than 1％，(2) cis-1，4-con-tent,93—97％，and (3) glass temperature，-110 to一114℃ (Table 1A)．However，the Mooney viscosity increases rapidly with [n] (Fig．1)．It is shown by stress-strain curves that a11 the cis-1，4-polybutadiene samples under examination do not crystallize during stretching (Fig．2)．The behaviour of cis-1，4-polybutadiene in milling is very sensitive to temperature．Carbon black compoundings have been carried out on an open laboratory mill at cylinder temperatures of 25，40，and 60。C，respectively． Smooth compounds from which vul-canizates with tensile strength over 200 kg／cm2 may be prepared can only be obtained at 25℃． When compounding is carried out at 40 or 60℃，cis-1，4-polybutadiene tends to crumble(Fig．4)，no smooth compound can be prepared，and the vulcanizate obtained loses tensile strength(Fig．3)．According to the following experimental results： (1)no gel formation，no signi ficant degradation，and no change in microstructure can be observed when cis-1，4一poly- butadiene is masticated either at 25℃ or at 40 or 60℃ (Fig．6 and Table 3)；(2)the effect of temperature on milling is reversible (Table 4)，it is presumed that the lOSS of tensile strength of the vulcanizate obtained from compound prepared at 40 or 60℃ is due to the difficulty of incorporation and dispersion of carbon black into the cis-1,4-polybutadiene rubber at a temperature above 40℃．This presumption is supported by the microscopic photographs of the CROSS-sections of the vulcanizates(Fig．5)．It is found that the tensile strength of the vulcanizate decreases rapidly as the mo-dulus(M300％) exceeds 60 kg／cm2 (Fig．8)．However，with a suitable amount of sulphur to control the degree of cross-14nking，vulcanizates of tensile strengths over 200 kg／cm2 can be obtained (Fig．8 and Table 1B)．The elastisity (Yerzley) and abrasive resistance of cis-1，4-polybutadiene vulcanizates are much better than those of natural rubber(Table 1B)．The effect of molecular weight of cis-1,4-polybutadiene on the mechanical proper-ties of the vulcanizate has been investigated． It is found that vulcanizates of tensile strength around 200 kg／cm2 can be obtained within wide range of molecular weights ([n] 2.5 to 3.6)，whereas elasticity increases with the M of the raw rubber(Fig．9)．
1963, 5(3): 123-130
Abstract:
The radiation copolymerization of tetrafluoroethylene and hexafluoropropylene was investigated at -78℃ with a 20，000-curie Co60 r-source． Values of the copolymeriza-tion rate constant were found to decrease with the increase of the amount of hexafluoro-propylene in the monomcr mixtures．This indicates that hexafluoropropylene has a lower copobrmerization reactivity． Values of n in the rate equation R=KIn are 0.60,0.78，and 0.85, as the mole fractions of hexafluoropropylene in the monomer mixtures are 0.1，0.5，and 0.7，respectively．This signifies that an increase in hexafluoropropylene concentration lowers the propability of biradical termination．A post-effect of the copolymerization was noticed． It was found that values of kp/kt in post-polymerization increase with the irradiation dosage．This fact is explained as due to the decrease in kt resulting from the enrichment of trapped polymeric radicals as a consequence of increased “in source”conversion on lfigher irradiation dosages．The effect of some common organic solvents and inhibitors on the copolymerization rate was also studied．Most of the results support a free．radical mechanism for this low-temperature liquid—phase radiation copolymerization；possibilities of simultaneous radical- cationic polymerization or of cationic polymerization，however，can not bc ruled out．
The radiation copolymerization of tetrafluoroethylene and hexafluoropropylene was investigated at -78℃ with a 20，000-curie Co60 r-source． Values of the copolymeriza-tion rate constant were found to decrease with the increase of the amount of hexafluoro-propylene in the monomcr mixtures．This indicates that hexafluoropropylene has a lower copobrmerization reactivity． Values of n in the rate equation R=KIn are 0.60,0.78，and 0.85, as the mole fractions of hexafluoropropylene in the monomer mixtures are 0.1，0.5，and 0.7，respectively．This signifies that an increase in hexafluoropropylene concentration lowers the propability of biradical termination．A post-effect of the copolymerization was noticed． It was found that values of kp/kt in post-polymerization increase with the irradiation dosage．This fact is explained as due to the decrease in kt resulting from the enrichment of trapped polymeric radicals as a consequence of increased “in source”conversion on lfigher irradiation dosages．The effect of some common organic solvents and inhibitors on the copolymerization rate was also studied．Most of the results support a free．radical mechanism for this low-temperature liquid—phase radiation copolymerization；possibilities of simultaneous radical- cationic polymerization or of cationic polymerization，however，can not bc ruled out．
1963, 5(3): 131-140
Abstract:
A new method of determination of the lateral order of cellulose fibres is proposed．1t is based on the measurement of the density of the fibre by the loss of weight method in a series of sodium hydroxide solutions of increasing concentration from zero to 2N．Due to the gradual penetration of the swelling agents into the fibre texture，the density values change step by step，the increments of density being plotted against sodium hvdroxide concentrations to yield the lateral order distribution curve．The slight error resulting from the partial solubility of the fibre in sodium hydroxide of higher concen-trations is corrected．The method is direct，simple，quick，of high power of resolution and good reproducibility．It seems to possess many advantages over current methods of tudying lateral order which in turn is the most essential dement in the characteriza-tion of the supermolecular structure of cellulose fibres．
A new method of determination of the lateral order of cellulose fibres is proposed．1t is based on the measurement of the density of the fibre by the loss of weight method in a series of sodium hydroxide solutions of increasing concentration from zero to 2N．Due to the gradual penetration of the swelling agents into the fibre texture，the density values change step by step，the increments of density being plotted against sodium hvdroxide concentrations to yield the lateral order distribution curve．The slight error resulting from the partial solubility of the fibre in sodium hydroxide of higher concen-trations is corrected．The method is direct，simple，quick，of high power of resolution and good reproducibility．It seems to possess many advantages over current methods of tudying lateral order which in turn is the most essential dement in the characteriza-tion of the supermolecular structure of cellulose fibres．
1963, 5(3): 141-145
Abstract:
With 0.1-1.5％ polyaluminophenylsiloxane as catalyst，the rate of curing of poly-methylphenylsiloxane resin increases．The apparent energy of activation of curing falls from 26 kcal／mole in the absence of the catalyst to 20 kcal/mole in its presence，being little affected by the amount of catalyst used．However，the apparent frequency factor of curing increases with the increase of the catalyst，being one order of magnitude higher with 0．6％catalyst than without．There are two stages in the thermal oxidative degradation of the thermally cured polymethylphenylsiloxane resin．The methyl groups decompose at a much lower tem-perature than the phenyl groups．The addition of the polyaluminophenylsiloxane during the curing of the resin raises the initial temperature of decomposition of the methyl group and lowers that of the phenyl group．With increasing amount of the catalyst used，the difference in the temperature of decomposition gradually diminishes．
With 0.1-1.5％ polyaluminophenylsiloxane as catalyst，the rate of curing of poly-methylphenylsiloxane resin increases．The apparent energy of activation of curing falls from 26 kcal／mole in the absence of the catalyst to 20 kcal/mole in its presence，being little affected by the amount of catalyst used．However，the apparent frequency factor of curing increases with the increase of the catalyst，being one order of magnitude higher with 0．6％catalyst than without．There are two stages in the thermal oxidative degradation of the thermally cured polymethylphenylsiloxane resin．The methyl groups decompose at a much lower tem-perature than the phenyl groups．The addition of the polyaluminophenylsiloxane during the curing of the resin raises the initial temperature of decomposition of the methyl group and lowers that of the phenyl group．With increasing amount of the catalyst used，the difference in the temperature of decomposition gradually diminishes．
1963, 5(3): 153-157
Abstract:
The value of dln[n]θ／dlnT for a polydimethylsiloxane fraction of Mn=1．4×106 has been determined in a temperature range of 10一100℃ by using a series of θ-solvents made of ethylbenzene-diethylphthalate．The compositions of these θ-solvents at various temperatures were determined by the precipitation threshold method of Elias，and finally confirmed by light scattering to give vanishing second virial coefficient．The results show that dln [n]θ／dlnT=0.45．Using the Flory-Fox theory of intrinsic viscosity we get din h20／dlnT=0.30，that is，the unperturbed dimension of polydimethylsiloxane mole-cult increases with increasing temperature．This seems reasonable in view of the dipole-dipole interactions of the Me2SiO units along the chain，so that the gauche conforma-tion has lower energy than the trams conformation．
The value of dln[n]θ／dlnT for a polydimethylsiloxane fraction of Mn=1．4×106 has been determined in a temperature range of 10一100℃ by using a series of θ-solvents made of ethylbenzene-diethylphthalate．The compositions of these θ-solvents at various temperatures were determined by the precipitation threshold method of Elias，and finally confirmed by light scattering to give vanishing second virial coefficient．The results show that dln [n]θ／dlnT=0.45．Using the Flory-Fox theory of intrinsic viscosity we get din h20／dlnT=0.30，that is，the unperturbed dimension of polydimethylsiloxane mole-cult increases with increasing temperature．This seems reasonable in view of the dipole-dipole interactions of the Me2SiO units along the chain，so that the gauche conforma-tion has lower energy than the trams conformation．
1963, 5(3): 158-162
Abstract:
