Annealing, polypropylene

FIGURE 3.43 Tensile strength as a function of birefringence for spun, hot-drawn, and cold-drawn and annealed polypropylene fibers. (From Nadella, H.P. Spruiell, J.E. White, J.L. J. Appl. Polym. Sci., 1978, 22, 3121. With permission.)... 

FIGURE 3.52 DTA traces for annealed polypropylene fibers. (From Jaffe, M. In Thermal Methods in Polymer Analysis, Shalaby, S.W. ed., Franklin Institute Press, Philadelphia, 1977, p. 93. With permission.)... 

Fig. 4. The dielectric loss at 100 Hz and 1 kHz of the unannealed and annealed polypropylene films from 4.2 to 10 K shown on expanded scale.

Figure 54 ows typical X-ray patterns of hard-elastic, annealed polypropylene... 

Fig, 54a-g. Wide-angle (a-c) and small-angle (d- ) X-ray diagrams of hard-elastic, annealed polypropylene a-c polypropylene film annealed for 0.75 h at 140 °C, a undrawn, b 73% extension, c recovered after extension to 73% strain d-g polypropylene fiber annealed for 1 h at 150 °C, d undrawn, e 50 % extension, f 100% extension, g recovered after extension to 100 % strain [reproduced from Noether, H. D., W. Whitney, Kolloid-Z. und Z. Polymere, 251.991-1005 (1973) by permission of the publishers. Dr. Dietrich Steinkopff Verlag, Darmstadt, West Germany)... 

The commercial poly-(4-methypent-1-ene) (P4MP1) is an essentially isotactic material which shows 65% crystallinity when annealed but under more normal conditions about 40%. For reasons given later the material is believed to be a copolymer. In the crystalline state P4MP1 molecules take up a helical disposition and in order to accommodate the side chains require seven monomer units per two turns of the helix (c.f. three monomers per turn with polypropylene and polybut-I-ene). Because of the space required for this arrangement the density of the crystalline zone is slightly less than that of the amorphous zone at room temperature. 

Figure 19 Chemiluminescence from oxidation of polypropylene containing 0.5 % wt. of Irganox 1010 at 150°C in oxygen. Line 1 represents the original polymer film line 2 is the same sample after 7,890 s of annealing at 130°C.

Figure 20 An increase of induction time of oxidation of polypropylene stabilized by Irganox 1010 (points 1) due to prior sample annealing at 130°C (points 2) in oxygen. The induction time corresponds to the time of cross-section of the straight line passing the CL inflexion point and time axis. It was determined for an oxygen atmosphere and temperature 150°C.

Figure 1. Specific charge (thick line) and discharge (thin line) capacity of tin electrode without annealing. Bronze interface is absent. Current collector - copper. Testing mode C/5. Counter electrode - lithium foil. Separators - 2 layers of unwoven polypropylene (Mogilev, Belarus).

Annealing can reduce the creep of crystalline polymers in the same manner as for glassy polymers (89,94,102). For example, the properties of a quenched specimen of low-density polyethylene will still be changing a month after it is made. The creep decreases with time, while the density and modulus increase with time of aging at room temperature. However, for crystalline polymers such as polyethylene and polypropylene, both the annealing temperature and the test temperatures are generally between... 

For polypropylene, by using the spectrum of an annealed sample and subtracting it from a quenched sample it is possible to obtain a difference spectrum characteristic of the amorphous regions of polypropylene 210). In Fig. 13, the difference spectrum characteristics of the amorphous phase of the quenched sample (a) is compared with the difference spectrum characteristic of the ordered phase of an annealed... 

Fig. 21. X-ray diffraction pattern of the annealing effect on polypropylene quenched to the CD-glass (control trace). The changes may suggest a glass transition at 340 to 360 K. Curve courtesy of Dr. W. W. Cox of the Research Laboratory of Hercules Inc.

Zannetti, R., Celotti, G. C., Fichera, A. and Francesconi, R. The structural effects of annealing time and temperature on the paracrystal-crystal transition in isotactic polypropylene. Makromol. Chemie 128, 137 (1969)... 

Fichera, A. and Zannetti, R. Thermal properties of isotactic polypropylene quenched from the melt and annealed. Makromol. Chemie 176, 1885 (1975)... 

The agreement between heats of fusion of the same polymer is excellent in some cases, but very poor in others. Obviously, in the case of polypropylene more work needs to be done before the heat of fusion of this substance will be known with any certainty. Heats of fusion calculated from the copolymer equation, Eq. (6), are uniformly low, except in the case of Rybnikar s data. As pointed out by Dole and Wunderlich (1957) this is probably due to the failure to measure the maximum melting of carefully annealed samples. Thus, Dole and Wunderlich (1959) found that the calorimetrically estimated melting point in the case of the carefully annealed copolyester, the 80/20 polyethylene terephthalate and sebacate, was 240° C, whereas the value calculated from Eq. (6) using the heat of fusion estimated from the calorimetric data of Smith and Dole (1956) was 245° C. The unannealed sample had a melting point of ca. 210°. 

Drawn isotactic polypropylene (iPP) fibres have been studied by using deuterated n-decane as a 2H NMR probe of the chain deformation ratio in the amorphous regions. It is observed that the slope P=A/(X2-X 1) (defined in the limit of low deformations) indeed depends on the annealing temperature [82]. Thus, annealing above the melting temperature Tm of the crystallites allows chains to relax to some extent. Then, the local deformation ratio in the amorphous phase Xt becomes lower than the macroscopic one X and depends on the annealing temperature, i.e., on the amount of chain relaxation. Therefore, such systems have strongly non-affine deformation at the chain scale. 

As it was demonstrated by staining the oxidized polypropylene and its observation by UV microscope, a high degree of inhomogeneity at the micron level was observed even for the most thoroughly annealed samples. In most cases this is clearly associated with the catalyst residues. An observation of microdomains in the oxidized polymer in which the degree of oxidation is by far pronounced than in the rest of polymer may be explained by the effect of higher oxidation state of transition metal ions M which interact directly with polymer ... 

Fig. 2. The plot of induction time of oxidation of polypropylene (oxygen, 150 °C) on time tA of the polymer annealing in nitrogen at 150 °C...

Materials. Biaxially oriented polypropylene (PP) films of 50 um thickness were obtained from 3M and have been described (2). PMDA-ODA (PI) was Kapton H polyimide from Dupont. Copper-plated PTFE films were obtained from Spire Corporation (Bedford, MA). They were prepared using the Ion Beam Enhanced Deposition (IBED) process in which a 100 nm thick Cu film was vapor-deposited onto a PTFE substrate in the presence of a beam of 400 eV Ar+ ions of 25 uA/cm2 (IQ). Shortly before SIMS analysis, the Cu film was removed slowly by peeling at 90° in ambient conditions. Metal-coated PI films were prepared by sputtering 50 nm Cr and 1 um Cu onto a 50 um thick Kapton film on both sides. Thermal annealing was performed in a vacuum chamber at 2xl0 6 torr using a quartz lamp as the heating source. The samples were held for 15 min at the desired temperature and then cooled down to ambient temperature inside the chamber for about 2 hours. Just prior to SIMS analysis, the metal films were peeled slowly at 90° and then immediately introduced into the vacuum chamber of the instrument. 

Fig. 32. Storage modulus, E, and mechanical loss ctor, tan 6, for GM6I polypropylene (M 400,000). Frequency 5 Hz X = IS. As-drawn, A after 60 min annealing at 135 °C...

The dynamic mechanical behaviour of ultra high modulus polypropylene is shown in Fig. 32. As in LPE, the modulus is temperature dependent, rising to a value of 25 GPa at —140 °C, which is rather more than half (he value of 42 GPa obtained from crystal measurements. Although the a and y relaxations of the isotropic polymer can be seen in the highly drawn material, the -relaxation is undetectable. On annealing, the modulus at high temperatures is markedly reduced, and a P-relaxa-... 

If isotactic polypropylene is quenched from the melt to room temperature a so-called smectic modification is formed which shows only two crystal reflexions. Cabarcos, Bbsecke, and Zachmann investigated the kinetics of the transition from this modification into the a-modification. Fig. 54 shows the change of wide angle scattering during isothermal annealing at 90 °C. One sees that the 040-reflexion of the a-modification appears after about 200 sec and continues to increase in intensity afterwards. The time until the constant temperature is reached is about 150 sec. Therefore we can say that most of the process occurs at constant temperature. If the same is done at 130 °C the process occurs so rapidly that it is almost finished as constant temperature is reached. 

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