Hot isotactic pressing

HIP hot isotactic pressing HVAC heating, ventilation, and air condi-... 

The effect of heterogeneous nucleation on the crystallization of isotactic polypropylene from the melt can be easily established as follows. A small amount of powdered polypropylene is well mixed with about 0.1 wt% of sodium benzoate in a mortar or by means of an analytical mill. Some of the mixture is transferred with a spatula to a microscope slide and melted at about 250 °C on a hot block. A cover slip is pressed on to the melt with a cork to obtain as thin a film as possible.The sample is held at 200-250 °C for some minutes and then allowed to crystallize at about 130 °C on the hot stage of the microscope an unadulterated polypropylene sample is crystallized in the same way. Both samples are observed under a polarizing microscope during crystallization,the difference in spherulite size between nucleated and untreated polypropylene can be seen very clearly. An ordinary microscope can also be used by placing polarizers on the condenser and eyepiece, and adjusting these to give maximum darkness. 

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... 

Four possible calibration curves of IR absorption ratio versus NMR tacticity were investigated for PP films hot pressed at 120-200 "C absorption at 10.02 pm referenced to bands 10.28 pm or 8.57 pm, and the absorption at 11.89 pm with the same reference bands i.e., ratios A10.02/A10.28, A10.02/A8.57, All.89/Al0.28 and A11.89/A8.57, respectively. Burfield and Lo [21] use the 10.28 pm band as reference to provide linear calibration curves for both ratios. Calibrations based on the 8.57 pm reference are curves that provide rather low sensitivity in the important high isotacticity (mm >0.8) region. Burfield and Lo [21] consider the 10.28 pm band as the most appropriate reference and consequently data for this band are described, i.e., ratios A10.02/A10.28 (Figure 6.5) and A11.89/A10.28 (Figure 6.6). A further advantage of calibrations involving the 10.28 pm reference is the possibility of representation as the simple linear equation ... 

Figure 6.5 Calibration curve for IR absorbance ratio A998/A973 versus NMR triad isotacticity. ( ) = high temperature annealed, (o) = hot pressed only, (A) = ambient temperature annealed. Reproduced with permission from D.R. Burfield and RS.T. hoi. Journal of Applied Polymer Science, 1988, 36, 2, 279.

Polymer pellets of isotactic polypropylene (iPP) were melted in a laboratory hot press for 15 min at 230 °C and 10 MPa, and then quenched in ice water (0 °C) or boiling water (100 °C). To control the crystallinity of the iPP sample, we annealed the sample sheets prepared at 0 °C for 2 hr at various temperatures from 40 to 140 °C. Square pillar shaped test specimens were cut out from a 1 mm thick sheet and used for the measurements. Double-edge notched sample specimens with the gauge length of 2 mm were used for the temperature dependence and the dumbbell shaped specimen with gauge length of 5 mm for the elongation speed dependence. 

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