Studies on ?-radiation treatment of poly(tetrafluoroethylene) powder

Abstract

SYNOPSISy-Irradiation of poly(tetrafluoroethy1ene) (PTFE) in the presence of air results in degradation of polymer chains by insertion of oxygen. At first, in the low-dose range below 400 kGy, a rise in crystallinity can be observed due to main chain scission in the amorphous part of the macromolecules. Dose increase up to approximately 1000 kGy causes progressive degradation of molecular weight as well as a growing degree of carboxylation of PTFE and increased concentration of trifluoromethyl groups in near-surface regions. At constant irradiation temperature, the properties of irradiated PTFE hardly depend on dose rate and starting material. The degree of carboxylation of the irradiated unsintered PTFE is appreciably lower in comparison with electron-irradiated PTFE under comparable conditions.

Radiation grafting of vinyl monomers onto poly(tetrafluoroethylene) powder produced by ? irradiation and properties of grafted poly(tetrafluoroethylene) filled low density polyethylene

“…The dominant effect of ionizing radiation on PTFE is a molecular weight decrease through a chain scission process. [1][2][3][4][5] Radiation induced chain scission is responsible for the increasing crystallinity of PTFE while decreasing the molecular weight. Chain scission can also act to relieve intramolecular stresses of molecules in the amorphous phase.…”

“…A further increase in crystallinity can also be observed by ␥ irradiation at a temperature just below the melting point of PTFE. [1][2][3][4][5] So, the dramatic decrease in the polymer molecular weight changes its melting and crystallization behaviors. The melting temperature of PTFE decreases with irradiation, 2 but the elevation in crystallization temperature of PTFE after irradiation is also indicated as being due to increased molecular mobility.…”

“…6 This result is explained by two competing processes: the crystallization of the molecules in the amorphous phase and the introduction of defects in the crystalline phase such as chain branching reactions. [1][2][3][4][5][6][7][8][9][10][11][12] The changes in crystalline content upon irradiation of PTFE can also be determined by increases in density and heat of fusion, the reduction and/or increase in intensity of absorption bands in the IR spectrum whose intensities are proportional to the amorphous content (775, 375, and 270 cm Ϫ1 ) and crystalline chain folding (286 cm Ϫ1 ), 2 and the change in the crystalline peaks in the X-ray diffraction. 6,13 The low crystalline PTFE was found to have higher G values for chain scission in comparison to high crystalline PTFE, because radiation induced chain scission mostly proceeded in the amorphous region of the polymer.…”

“…6,13 The low crystalline PTFE was found to have higher G values for chain scission in comparison to high crystalline PTFE, because radiation induced chain scission mostly proceeded in the amorphous region of the polymer. 1,11 Chain degradation was shown to be affected by the dose rate; but, particularly at very low dose rates, the rate of chain scission was reduced. 1 Radiation induced changes in the number-average molecular weight (M n ), and hence the chain scision, can be followed by melt viscosity and heat of crystallization measurements.…”

“…1,11 Chain degradation was shown to be affected by the dose rate; but, particularly at very low dose rates, the rate of chain scission was reduced. 1 Radiation induced changes in the number-average molecular weight (M n ), and hence the chain scision, can be followed by melt viscosity and heat of crystallization measurements. 1 It was also found that radiation induced crosslinking of PTFE could only be produced by irradiation with high energy radiation under a vacuum in the molten state at around 340°C.…”