Compression molding copolyester

Fig. 18. Randomizing processes in the aromatic copolyesters transesterification of PHBA/PHNA mixture during compression molding at 450°C...

Various process steps were used to determine their Influence on the morphological nature of liquid crystalline copolyester films. Compression molding was used to form quiescent films, while extenslonal deformation above and below the onset of fluidity, as well as shear deformation above the onset of fluidity was used to make non-quies-cent films. It Is a basic result that molecular orientation can only be achieved when the deformation is done while the polymer is In a liquid crystalline melt state. Experimental details are given In the subsection Materials and Processing, while an interpretation is offered in the discussion in the subsection Morphological and Process Consideration. ... 

Materials and Processing. Copolyesters of poly(ethylene terephtha-late) (PET) and para-oxybenzoic acid (FOB) were supplied by the Tennessee Eastman Corporation. Past work Indicates the copolyesters form thermotropic liquid crystalline phases at compositions containing more than 30 mole% POB (26,27,28). The composition of the copolyester studied here contains 60 mole% POB. Quiescent liquid crystalline films were made by compression molding the copolyester at 210, 230, 255, and 285 C, and followed by a quench Into Ice water, ambient air, or cooled In the press with the power off. Film thicknesses ranged between 0.05-0.15 mm. Another sa(q>le of the 40/60 PET/POB copolyester was melted at 270 °C In a Mettler hot stage, manually sheared between glass slides, and then ambient air cooled. 

Figure 4 Typical Iso-lntenslty Contour Patterns oC Compression Molded 40/60 PET/POB Copolyester A) 255 c, Press Cooled B) 285 C, Ice Water Quenched.

Figure 8 Typical SEM Micrographs of Compression Molded 40/60 PET/ POB Copolyesters A) 255 °C, Ice Water Quench B) 210 C, Air Quenched.

Viscosity measurements at low shear rates were made with a Rheome-trics System 4 or Rheometrics RMS-800/RDS-II spectrometer in either cone and plate (cone angle =0.1, radius = 25 mm) or plate and plate (radius = 25 mm, distance = 1 mm). For higher shear rates viscosity measurements were made with an Instron capillary viscometer. A capillary with L/D = 51.4 and D = 0.889 mm was used. Sample discs were prepared by compression molding of the predried (at least 3 days at 125°C in vacuum) copolyesters at 250°C. Prepared discs were dried at 125°C in vacuum for 5 hr before use. The correction for non-Newtonian behavior was applied, but entrance pressure corrections were neglected. 

Figure 9.6 DSC thermograms for compression-molded 60/40 HBA/PET copolyester specimens during (a) the heating cycle and (b) the cooling cycle at a rate of 20°C/min, where curve (1) is for the first heating or cooling cycle, curve (2) is for the second heating or coofing cycle, and curve (3) is for the third heating or cooling cycle.

Figure 9.28 DSC thermograms for compression-molded 73/27 HBA/HNA copolyester specimens annealed at different temperatures ...

Figure 9.29 Variations of G (O) and G" ( ) with time for a compression-molded 73/27 HB A/HNA copolyester specimen placed in the cone-and-plate fixture at 320 °C and annealed there. (Reprinted from Han et al.. Molecular Crystals and Liquid Crystals 254 335. Copyright 1994, with permission from Taylor Francis Group.)...

Figure 9.38 Trace of first normal stress difference of a compression-molded 73/27 HBA/HNA copolyester specimen during transient and steady-state shear flow, and dnring the relaxation after cessation of steady-state shear flow. The normal stress before applying a sudden shear flow to the specimen is taken to be zero. (Reprinted from Han and Chang, Journal of Rheology 38 241. Copyright 1994, with permission from the Society of Rheology.)...

Figure 9.40 Plots of (t, y) versus yt for compression-molded 73/27 HBA/HNA copolyester specimens at 290°C for various shear rates (s ) (O) 0.05, (A) 0.1, and ( ) 0.3. A fresh specimen was used for each applied shear rate. Each specimen, after being cooled from 320 to 290 °C, was annealed for 5 min before being subjected to shear flow. The unrelaxed normal...

Zini et al. [50] prepared composites of a bacterial copolyester poly(3-hydroxybutyrate-co-3-hydroxyhexanoate], P(3HB-co-3HH), reinforced with flax fibers by compression molding. In order to improve fiber-matrix adhesion in composites, fibers chemically modified at the surface (by acetylation or by short-chain-PEG grafting] were also used. The best results were obtained with surface acetylated fibers. In the flax fiber composites the crystallization rate of P(3HB-co-3HH] remarkably increased compared with that of the plain polyester. The fibers displayed a nucleating effect on P(3HB-co-3HH] crystallization, whose magnitude depended on fiber surface chemistry. This feature was confirmed by the appearance of trans-crystallinity in isothermal crystallization experiments run in a hot stage of a polarized optical microscope. 

Isayev AI, Modic M (1987) Self-reinfOTced melt processible polymer composites extrusion, compression, and injection molding. Polym Compos 8 158 James SG, Donald AM, MacDonald WA (1987) Blends of a liquid crystalline copolyester with polyethersulphone. Mol Cryst Liq Cryst 153 491 Jerman RE, Baird DG (1981) Rheological properties of copolyester liquid crystalline melts. I. Capillary rheometry. J Rheol 25 275... 

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