Fluorinated-pitch PTFE

The heat-treatment for PTFE containing the various amount of fluorinated-pitch [PTFE / fluorinated-pitch polymer-blend PTFE / FP] was carried out at 350 °C + 5 °C for 30min. Figure 2 shows the thermal properties of heat-treated PTFE with fluorinated-pitch. The melting and the crystallization temperatures shift to lower temperatures by addition of fluorinated-pitch. And also, the heat of crystallization (AHc) decreased with increasing of amount of fluorinated-pitch. 

Table I shows the mechanical properties of the carbon fiber-reinforced PTFE (PTFE composite non-crosslinked) and the carbon fiber-reinforced PTFE with fluorinated-pitch (PTFE / FP composite thermo-chemical crosslinked). For the tensile test with a direction of 45 ° for plane-woven carbon fabric, the tensile strength of the PTFE / FP composite was about 2.3 times higher than that of the non-crosslinked PTFE composite. Moreover, the Young s modulus of the crosslinked composite was about 2.6 times higher than that of the PTFE composite. The tensile strength and Young s modulus are results of 0 ° or 90 ° direction for the fabric reflected the carbon fiber strength and the modulus.

Fig. 5. Cls ESCA spectra of solid type fluorinated pitch, (CF) and PTFE (A) solid type fluoride prepared at 70 C (B) graphite fluoride, (CF) (C) PTFE. (Quoted from the poster material of Ref. [18]).

Compared with PTFE, fluorinated pitch has a higher oxygen transmission constant, but a lower separation ratio a. 

The materials for the experiments were an aqueous dispersion PTFE (FLUON XAD -911 average diameter of particles 0.25 pm, concentration 60 wt%, Mn 1.4 x 106, viscosity at 25 °C 20 mPa-s, Asahi-Glass Fluoropolymers Co. Ltd.), and fluorinated-compound such as fluorinated-pitch (Rinoves P N-7-M average diameter of particles 1.2 pm, atom ratio of F/C 1.6, Mn 2.0 x 103, Osaka Gas Chemicals Co. Ltd.) [12, 13]. And also the plane-woven carbon fabric (TORAYCA T-300, C06142, TORAY Industries, Inc.) was used for the mechanical tests such as the tensile and the flexural tests. 

The polymer-blend dispersions of PTFE and fluorinated-pitch with various concentration of fluorinated-pitch have been coated on stainless steel (SUS-304). The various coated polymer-blend were heat-treated at 350 °C 5 °C for 30 minutes. Further, samples were subjected to EB irradiation with a 200keV from EB accelerator (CURETRON , NHV Corporation) up to 1000 kGy at 330 °C 3 °C in nitrogen gas atmosphere. 

For mechanical test such as tensile test and flexural test, the impregnation of polymer-blend to the carbon fiber was carried out several soakings of the fiber in the polymer-blend dispersion consists of PTFE (98.2 wt%) and fluorinated-pitch (1.8 wt%). A sheet of chemical crosslinked pre-forming sample was prepared under the pressure at around 20 MPa and then heat-treated at 350 °C 5 °C for 30 minutes. Samples were irradiated by EB up to 1000 kGy at 335 °C 3 °C in nitrogen gas atmosphere. 

Chemical Crosslinking of PTFE using Fluorinated-Pitch... 

Figure 1 shows SEM photographs of each powder of PTFE and fluorinated-pitch. For PTFE, the average particles sizes were few pm caused by coaggregation of sub-micron size fine particles. In the case of fluorinated-pitch, it was found a similar structure to graphite fluoride (CF) , that size was about 1 pm or 2 pm. 

The present experimental results show that the changes of thermal properties of PTFE with fluorinated-pitch after heat-treatment at around 350 °C in the molten state are completely different from those of PTFE non-additive fluorinated-pitch. The changes and the behavior of thermal properties in the... 

Figure 2 The thermal properties of heat-treated PTFE with fluorinated-pitch as Junctions of amount offluorinated-pitch.

The crosslinking between PTFE polymer chains and fluorinated-pitch should prevent crystallization of molecules from the molten state. When the crosslinking density is low, the molecules with rather long chain between crosslinking points might ciystallize, where the crystal size would be small and also the ratio of crystalline against amorphous parts would decrease. The DSC results are well explained by above model. 

The first degradation step of fluorinated-pitch should be induced crosslinking reaction in PTFE molecules. That is, the crosslinking would be occurred in PTFE molecules through thermal chemical reaction with decomposion of fluorinated-pitch without EB irradiation. 

Figure 3 The solid-state I9FNMR spectrum of heat-treated PTFE (98.2 wt%) with fluorinated-pitch (1.8 wt%). The magic angle spinning frequency is 12 kHz. The measurement temperature is at 150 X.

Figure 4 The TGA curves of fluorinated-pitchf PTFE and heat-treated PTFE with fluorinated-pitch (1.8 wt% additive PTFE/FP). (a) Temperature range of 0 X to 900 X, (b) Temperature range of400 X to 600 X.

Table I. The tensile and flexural properties of the carbon fiber-reinforced PTFE and the carbon fiber-reinforced PTFE with fluorinated-pitch. Volume of carbon fiber was 54.3 %...

The synergistic crosslinking was carried out, that is, EB-crosslinking treatment was performed after thermo-chemical crosslinking treatment of PTFE with fluorinated-pitch (1.8 wt% additive). The thermal properties of obtained crosslinked PTFE were examined by DSC analysis shown in Table II. The melting and the crystallization temperatures of radiation-crosslinked PTFE (RX-PTFE), thermo-chemical-crosslinked PTFE (CX-PTFE), synergetic-crosslinked PTFE (thermo-chemical and radiation SX-PTFE) shift to lower temperatures, compared with PTFE. 

Table III shows the flexural properties of RX-PTFE composite with an EB dose of 500 kGy and SX-PTFE composite (fluorinated-pitch 1.8 wt% additive) with an EB dose of 500 kGy. For the three-point bending test of the sixth plys laminate panels, the flexural strength of SX-PTFE composite was about 1.1 times higher than that of the RX-PTFE composite. The flexural modulus of SX-PTFE composite was about 1.3 times higher than that of RX-PTFE composite. It was found that the flexural properties of SX-PTFE were improved, compared with RX-PTFE composite.

Figure 5 The tensile strength and the Young s modulus with the direction of 45 ° tensile properties of one ply sheet composites consist ofplain-woven carbon fiber-reinforced RX-PTFE and the carbon-fiber-reinforced SX-PTFE (fluorinated-pitch 1.8 wt% additive) as a function of EB dose.

A convenient method for defining helical symmetry and calculating the distribution of Intensity In a fiber pattern was devised by Cochran, Crick and Vand (CCV) (4). As Indicated in Figure 1, the molecular conformation is treated as a regular series of diffraction units uniformly spaced along a helix of pitch, P, with axial separation, s. In PTFE, one helix defines the carbon positions two helices define fluorine positions. If there is a meaningful translational Identity, c, It follows that P/s will be the ratio of small whole numbers ... 

Mesophase pitch, derived from coal tar, reacts smoothly with fluorine to give pitch fluoride [147, 148] with a composition between CFi 3 and CFi 6, as a yellowish white solid which differs from graphite fluoride in that it is soluble in some fluorocarbon solvents. Consequently, thin films of pitch fluoride may be deposited on materials and the resulting surfaces have been claimed to have even lower surface energies than PTFE. 

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