Stretching-quenching process

PET/iPP The transcrystallites fabricated through a slit extrusion hot stretching-quenching process Li et al. 2004... 

Li et al. utilized another approach, melt extrusion-hot stretching-quenching , to prepare several MRCs such as PET/PE [9], PET/PP [3], PC/PE [10], PA/PE [11] and Poly(phenylene sulfide) (PPS)/PP [12] MRCs. The factors affecting structures, morphologies, mechanical, rheological and crystallization properties of the MRCs such as composite composition, hot stretch ratio and viscosity ratio, etc., have been studied in detail. This chapter briefly describes the preparation, structure and properties of MRCs obtained by this specific melt extrusion-hot stretching-quenching process. 

Microfibril reinforced polymer-polymer composites (MRCs) based on two thermodynamically nonmiscible thermoplastics with different melting temperatures (T ) are prepared through a melt extrusion-hot stretching-quenching process, during which the high-melt-temperature component as the dispersed phase in situ deforms into microfibrils. The post... 

There exist a limited number of studies on the occurrence of transcrystaUinity in MFC. Li et al. [38,42,43] studied the crystal morphology of iPP/PET in situ MFC, prepared by a slit extrusion, hot stretching-quenching process, and foimd that transcrystallinity occurred aroimd the PET in situ microfibrils. The authors propose different nucleation mech-... 

Li Z M, Li L B, Shen K Z, Yang W, Huang R and Yang M B (2004) Transcrystalline morphology of an in situ microfibrillar poly(ethylene terephthalate)/poly(propylene) blend fabricated through a slit extrusion hot stretching-quenching process, Macromol Rapid Commun 25 553-558. 

F. 8.1 Schematic diagram depicting the melt extmsion-hot stretching-quenching process... 

The data in this work were obtained by quenching either uniaxially stretched samples for which the low thickness of the specimens allows rapid cooling, or samples deformed in simple shear where higher thickness of the specimens was required in order to perform the scattering experiments along the three principal shear directions. For both types of flow, special devices were developed to control the flow kinematics in the molten state as well as the quenching process which freezes the molecular orientation. These devices are briefly described in the next paragraphs. 

The orientation of the spun monofilaments and, consequently, the draw ratio necessary for producing a satisfactory product depend on the stretch rate during spinning and quenching, just as they do in the air-quench process. The larger the stretch rate, the higher the spin-line stress, the higher the orientation, and the lower the required draw ratio. 

The process uses crystallizable polymers, of which the most important in PET. The first step is to injection mould (hence the name) a parison, or preform as it is more usually termed here. The preform is closed at the bottom and is considerably shorter and thicker than the final bottle. It is rapidly cooled (quenched) by using chilled water to cool the injection mould and this ensures that it is in its amorphous condition, i.e. no crystalline structure. Next it is reheated with infra-red elements to above its Tg, about 90-100 C for PET and enters the bottle mould and the mould is closed. The blow pin enters and pushes the soft preform downwards almost simultaneously the blow occurs, compressed air blowing the material outwards. The result is biaxial orientation - downwards from the movement of the blow pin, outwards from the action of the expanding air. The orientation induces crystallization, but in the form of lamellar crystals rather than spherulitic ones. This type of crystallization is strain-induced, and is characteristic of synthetic fibres and film, e.g. Melinex. It gives a transparent product with enhanced physical properties, both important for bottling carbonated drinks. The alternative name for the process is the stretch-blow process. Its main feature as a process is the control of the crystallinity of the polymer at its different stages. 

Inspired by the intrinsic deformation nature of polymer melt, various proposals have been put forward to constmct particular structure in polymer blend, aiming at the achievement of excellent performance. One of the typical examples is the methodology of in situ micro/nanofibrillation, in which, under the process of melt extrusion-hot stretching-quenching, the spherical dispersion domains in situ deform into micro/nanofibrils, realizing the scalable achievement of in situ micro/nanofibrillar composites, accompanied with greatly improved mechanical... 

Li ZM, Lu A, Lu ZY, Shen KZ, Li LB, Yang MB (2005) In-situ microfibrillar PET/iPP Blend via a slit die extrusion, hot stretching and quenching process influences of PET concentration on morphology crystallization of iPP at a fixed hot stretching ratio. J Macromol Sci Part B Phys 44(2) 203-216... 

Poly(ethylene terephthalate) film is produced by quenching extruded film to the amorphous state and then reheating and stretching the sheet approximately three-fold in each direction at 80-100°C. In a two-stage process machine direction stretching induces 10-14% crystallinity and this is raised to 20-25% by... 

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