Semicrystalline polymers, thermal analysis

Adiabatic Compression Heating Melting of polymers by adiabatic compression has been shown to be feasible for processes such as injection molding (2). Discuss this method, in principle, in terms of an order-of-magnitude analysis of the terms of the thermal energy balance for an amorphous (PS) and a semicrystalline polymer (LDPE). Use the data in Appendix A. 

The glass-transition temperature, melting point, heat distortion temperature, thermal degradation temperature, ete. are important parameters affecting the application and processing of semicrystalline polymer materials. These thermal parameters can be obtained via differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, etc. 

The overall rate of isothermal crystallization of PTT (semicrystalline polymer) can be monitored by thermal analysis through the evolution of heat of crystallization by DSC as depicted in Figure 10. The sample is isothermally crystallized at preselected crystallization temperature (T) until complete crystallization. Half time of crystallization for the polymer is estimated from the area of the exotherm at r = const, where it is the time taken for 50% of the crystallinity of the crystallizable component to develop. The rate of crystallization of PTT can be easily characterized by the experimentally determined reciprocal half time, (tg j) . ... 

A similar comparison of DSC and quasi-isothermal TMDSC for poly(ethylene terephthalate) is given in Fig. 3.92. The reversible melting is substantial and seems to contradict the schematic of melting developed with Fig. 3.76. More will be said about this topic in Chaps. 4—7 in connection with the description of temperature modulation in the melting range. The picture that has developed from this thermal analysis is that the globally metastable, semicrystalline, and flexible polymers in their... 

The large multiplicity of phases, of which many are mesophases, is typical for macromolecules. The old two-phase model for semicrystalline polymers is in need of considerable extension. Most of the phase areas are metastable and have, in addition, only nanometer dimensions [7]. Only when a full characterization has been completed, can an attempt be made to link structure and properties, the central goal of thermal analysis of materials. 

D2117 Test Method for Melting of Semicrystalline Polymers by the Hot Stage Microscopy Method D3417 Test Method for Heats of Fusion and Crystallization of Polymers by Thermal Analysis... 

One of the most useful, and practical, concepts in the characterization of a semicrystalline polymer Is the degree of crystallinity. Mechanical and physical properties depend on morphology but are closely related to the degree of crystallinity. Many methods, including A"-ray diffractometry, density determination, thermal analysis, and spectroscopic techniques have been used, but the degree of crystallinity cannot be measured absolutely since it is defined by the method of measurement. This has led to the questioning of the meaning of polymer crystallinity. Exact comparability between the values determined by the different methods should not be expected because some assumptions are invariably made in each case. 

Wunderlich B (2003) Reversible crystallization and the rigid-amorphous phase in semicrystalline macromolecules. Prog Polym Sci 28(3) 383 50 Wunderlich B (2005) Thermal analysis of polymeric materials. Springer, Berlin Wunderlich B, Cormier C (1966) Seeding of supercooled polyethylene with extended chain crystals. J Phys Chem 70(6) 1844-1849... 

JOSEPH D. MENCZEL PhD. a recognized expert in thermal analysis of polymers with some thirty years of industrial and academic experience, is Assistant Technical Director at Alcon Laboratories. He has researched more than 120 polymeric systems in which he studied calibration of DSCs, glass transition, nucleation, crystallization, melting, stability, mechanical and micromechanical properties of polymers, and polymer-water interactions. Dr. Menczel holds six patents and is the author of seventy scholarly papers. He is the author of two chapters in the book Thermal Characterization of Polymeric Materials In conducting DSC experiments, Dr. Menczel found a crystal/amorphous interface in semicrystalline polymers, which later became known as the rigid amorphous phase. He is also credited with developing the temperature calibration of DSCs for cooling experiments,... 

A polymer s Tg and 7 can be determined in several ways. A convenient method is thermal analysis. Measurements are carried out in a calorimeter that scans temperature and measures the quantity or rate of heat absorbed by a substance compared to a standard. Scans for an amorphous and a semicrystalline polymer are shown schematically in Fig. 19.9. 

Several examples, including polyethylene (PE), poly(trimethylene terephthalate) (PTT, poly(butylene terephthalate) (PBT), poly(lactic acid) (PLA), and others are shown in order to present the rationale behind quantitative thermal analysis of melting in several semicrystalline polymer systems. 

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