Polymer films melt pressing

The fusion temperature of these polymers is low enough to allow the spinning of fibres and melt pressing of films 263). They can also be blended with normal thermoplastics such as polystyrene or polyethylene oxide)2711. The conductivity shows a percolation threshold of about 16% which is expected for a random distribution of conducting spheres. 

Many polymers, including polyethylene, polypropylene, and nylons, do not dissolve in suitable casting solvents. In the laboratory, membranes can be made from such polymers by melt pressing, in which the polymer is sandwiched at high pressure between two heated plates. A pressure of 13.8—34.5 MPa (2000—5000 psi) is appHed for 0.5 to 5 minutes, at a plate temperature just above the melting point of the polymer. Melt forming is commonly used to make dense films for packaging appHcations, either by extmsion as a sheet from a die or as blown film. 

High molecular weight, rather high melting polymers were obtained and could be melt pressed or cast into films or spun into fibers. These polymers were soluble... 

Ester interchange between the additive and polymer would be expected if the mixture were held for an excessive time in the melt. In order to avoid the potential for interchange, the blendings were conducted in solution and heated only for a time necessary to melt press films for flammability testing. An alternative method of film preparation by solvent casting of films was discarded due to difficulties in preparing uniform, sufficiently thick, solvent free films for evaluation. 

Ir- and F-NMR spectra were determined for all soluble polymers. Most of the HFB polymers (8a-e) showed good solubility in common solvents (e.g., THF, CHCI3) whereas, most polymeric derivatives of the bishaloaromatics (9a-f), especially those with PFB as comonomer, were insoluble. Inherent viscosities ranging from 0.1 to 0.7 were obtained for soluble polymers. Coherent films could be either solution cast or melt pressed for a number of polymers. 

For higher molecular weight polymers, films were cast from solution for soluble polymers and melt pressed ca. 300 for insoluble polymers. 

Polymer Characterization. Melt-pressed films of the nylon samples were examined using a Nicolett 5DX FTIR. The samples were pressed at 240° C - 260° C at 4,000 to 20,000 psi. Samples in 88% formic acid were precipitated into methanol and also examined as KBR pellets. All samples were scanned a minimum of 100 times. 

Zhang et al. studied the effect of conductive network formation in a polymer melt on the conductivity of MWNT/TPU composite systems (91). An extremely low percolation threshold of 0.13 wt% was achieved in hot-pressed composite film samples, whereas a much higher CNT concentration (3-4 wt%) is needed to form a conductive network in extruded composite strands. This was explained in terms of the dynamic percolation behavior of the CNT network in the polymer melt. The conductivity of extruded strand showed a hopping resistivity dominated behavior at low concentrations and a dynamic percolation induced network dominated behavior at higher concentrations. It was shown that a higher temperature can reduce the filler concentration required for the dynamic percolation to take effect. 

The samples used in this study are listed in Table I with selected characterization data. Also given are our notations for the samples. S and B represent polystyrene and polybutadiene, respectively. The block polymers are denoted S/Bi, S/B2, etc. The letters identify the polymer components with the first letter indicating the center segment. The polymers were isolated from the polymerization solution by precipitation into cold (0°C), well-stirred methanol. After careful drying in a vacuum oven (25°C), film samples were prepared by melt pressing at temperatures ranging from 25 °C for homopolybutadiene to 150 °C for homopolystyrene. 

The detected current is influenced considerably by any incomplete contact between sample and electrode, bubbles, grain boundary, and so on. So it is necessary to be careful in preparing the contact conditions for the sample and electrode interface in polymer systems. When the polymers are flexible films or soft paste, good contact is obtained by simply pressing. For hard or brittle polymer systems, it is difficult to get good contact by the pressing pressure. To improve the contact, it is necessary to melt the polymer material or to sputter electrode material on the... 

Thin films of isotactic or elastomeric [51] polypropylene can be prepared from pellets by melt pressing. For this purpose several iPP or ePP pellets are placed between two sheets of thick aluminum foil and are subjected to pressure in in a hot press (T - 175°C pressure ca. 1-10 tons). Careful Wear appropriate safety shields and gloves After cooling the sample down to ambient temperature, the foil is unwrapped. If the polymer sticks to the foil, the film can be removed after cooling it down below the glass transition temperature e.g. in liquid nitrogen. Careful For... 

It is usually difficult to isolate and characterize a copolymer from a melt-processed polymer blend. Model studies of copolymer formation between immiscible polymers have been performed either in solution (where there is unlimited interfacial volume for reaction) or using hot-pressed films of the polymers (where the interfacial volume for reaction is strictly controlled at a fixed phase interface). Model smdies using low molecular weight analogs of the reactive polymers are useful but their applicability to high molecular weight reacting systems is limited. 

The linear PE studied was Marlex 6015 obtained from Phillips Petroleum Co. The polymer powder was compression-molded between Teflon-coated aluminum foil at 170°C. Temperature was maintained for 15 min prior to compression for 5 min. The sample was then allowed to cool slowly to room temperature with no pressure while still in the platens of the press. Thin films were obtained which showed no macroscopic melt flow orientation and which were less than 0.002 in. thick. This sample preparation will be referred to as slow-crystallized. 

Sample preparation In order to measure the interfacial thickness, always bilayer specimens were prepared containing a thick substrate (about 1mm) and a thin film on top (in the range from 15 to 100 nm). The substrates were melt-pressed between two silicon wafers at 200 °C. The thin films were prepared by spin-casting of the polymer solutions onto a silicon wafer and the resulting films were floated off onto a water surface. The floating films were then picked up with the substrate and dried at elevated temperatures in a vacuum oven. 

Melt pressing is a first technique which results in thin polymer films. Polymer granules are heated between electrically heated plates, which can be forced against each other. Since this is a discontinuous process, it has little industrial application. However, if the mould plates are micro-structured, structured polymer sheets can be developed. In this case, the term hot-embossing is generally applied. 

Samples were melt pressed in a vacuum laboratory hot press (Carver Press, Model C) at 160°C for 30 min. The molded films were then allowed to cool to room temperature under vacuum. A dual temperature chamber for the melt crystallization experiments consists of two large thermal chambers maintained at the melt temperature (Ti = 160°C) and the crystallization temperature (Ts = 81°C, 83°C, 86°C, 89°C, 92°C or 96°C). After 5-10 min at Ti, the copper sample cell was transferred rapidly ( 2 s) to the other chamber by means of a metal rod connected to a pneumatic device. A detailed description of the arrangement of the sample and of the two detectors used to measure WAXS and SAXS simultaneously has been provided previously [32]. Each polymer sample within the copper cell was 1.5 mm thick and 7 mm in diameter and was contained between two 25 im thick Kapton films. The actual sample temperature during crystallization (T2) and melting (Ti) was monitored by means of a thermocouple inserted into the sample cell. The crystallization temperature was usually reached 120 s after transfer without overshooting. Under isothermal conditions the fluctuations in the sample temperature are less than 0.5°C. Unless stated otherwise, all references to time are times elapsed after transferring the sample to the crystaUization chamber. 

Stereo-complex films were reported by Masutani et al7 % combining bifunctional PLLA and PDLA pre-polymers, multi-stereo-block copolymers having different block lengths and sequences are obtained. The resultant copolymers are readily fabricated into transparent films by hot-pressing. The films present excellent thermal stability and thermo-mechanical properties because of the easy formation of stereo-complex crystals. This synthetic method based on tbe dual terminal couplings allows obtaining stereo-block copolymers of PLLA and PDLA showing excellent thermo-mechanical properties and melt processability. 

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