Polyamides processing conditions

Nylon (polyamide fibers). The chemical structure of the nylon fiber looks just like the nylon resin. The polymerization processes are the same the numbering systems are the same and the two most important nylon fibers are the same nylon, 6 and 66. The difference is the length of the molecule in comparison to the cross-section. Thats regulated by the polymerization process conditions. 

Plastics. Plastics are the polymeric materials with properties intermediate between elastomers and fibers. In spite of the possible differences in chemical structure, the demarcation between fibers and plastics may sometimes be blurred. Polymers such as polypropylene and polyamides can be used as fibers and plastics by a proper choice of processing conditions. Plastics can be extruded as sheets or pipes, painted on surfaces, or molded to form countless objects. A typical commercial plastic resin may contain two or more polymers in addition to various additives and fillers. Additives and fillers are used to improve some property such as the processability, thermal or environmental stability, and mechanical properties of the final product. 

In order to form PTFE polyamide block copolymers high shear rates are necessary under melt processing conditions, to receive a good distribution and a further break down of PTFE micropowder particles. The particle size of the added PTFE micropowder is in the order of 2-8 pm. The crucial point for a successful coupling reaction is the contact between the carboxylic acid groups on the surface of the PTFE microcrystals and the amide groups of the molten polyamide matrix. As a result, a very homogeneous distribution of PTFE in the PA matrix is observed after reactive extrusion [21-23]. 

Another interesting phenomenon - the fractionated crystaUisatiOTi of PTFE -could be observed by DSC. PTFE melts near 325°C and crystallises near 310°C. The crystallisation behaviour of the dispersed PTFE phase in a PA matrix is influenced by the melt viscosity of the polyamide matrix, the processing conditions in twin-screw extruders and the irradiation dose of PTFE. With increasing... 

The mechanical properties of the surface-modified products were examined by a special shear test. After reactive surface modification under optimised chemical and technological conditions, the test specimens were cut and the pieces were bonded by special adhesives. The coimected pieces were examined in a shear test and the shear strength was determined in dependence on the chemical and processing conditions. The best results for polyamides were obtained for polyacrylic acid as the modifier with an increase of the shear strength from 28 MPa (non-modified polyamide) up to 37 MPa for polyacrylic acid-modified polyamide surfaces. 

Polymer clay nanocomposites have, for some time now, been the subject of extensive research into improving the properties of various matrices and clay types. It has been shown repeatedly that with the addition of organically modified clay to a polymer matrix, either in-situ (1) or by melt compounding (2), exfoliation of the clay platelets leads to vast improvements in fire retardation (2), gas barrier (4) and mechanical properties (5, 6) of nanocomposite materials, without significant increases in density or brittleness (7). There have been some studies on the effect of clay modification and melt processing conditions on the exfoliation in these nanocomposites as well as various studies focusing on their crystallisation behaviour (7-10). Polyamide-6 (PA-6)/montmorillonite (MMT) nanocomposites are the most widely studied polymer/clay system, however a systematic study relating the structure of the clay modification cation to the properties of the composite has yet to be reported. 

Lamellar dispersion of polyamide domains within HDPE matrix has been achieved by proper choice of rheology of the resins and processing conditions [Subramanian, 1985]. The platelet shape of PA domains enhanced its barrier properties against permeation by gases or liquids. The technology was commercialized and marketed by DuPont (Selar RB), aiming at packaging applications... 

Blends of polyamide copolymers with butyl acrylate copolymers (Durethan C, with PA being a copolymer of e-caprolactam and other monomers) can be blown into films. The recommended processing conditions are screws having L/D = 25-33 and compression ratio = 3.5-4.0, barrel feed zone at T = 225-260°C and melt temperature of T = 250-280°C. For multi-layer films, adhesion between layers can be achieved either by addition of an adhesion promoter to either of the two materials or (preferably) by co-extrusion with an adhesive layer. 

Linear aliphatic homopolyamides are partially crystalline materials. Therefore they are characterized by both an unordered amorphous state and an ordered crystalline state. The latter may exhibit polymorphism. The extent to which each state or specific modification is represented depends, for a given chemical structure, considerably on processing conditions and treatment operations. It affects the properties of the shaped polyamide product. Thus the corresponding structure parameters are of importance for optimizing fiber processes as well as for assessing the performance of fiber products in particular applications. 

Yeh JT, Chao CC, Chen CH (2000) Effects of processing conditions on the barrier properties of polyethylene (PE)/modified polyamide (MPA) and modified polyethylene (MPE)/polyamide (PA) blends. J Appl Polym Sci 76 1997-2008... 

Fiber-forming PP melts behave Uke non-Newtonian viscoelastic liquids having drop of viscosity with increasing share rate. The declination from a Newtonian flow and elasticity of PP melt are essentially higher comparing with polyamides and polyesters. Typical values of melt viscosity at processing conditions are 150-450 Pa s [4]. 

Processing conditions or chemical reactions occurring in one or both phases of the blend can strongly affect the phase inversion. Of course, these two parameters have a direct effect on the viscosity ratio of the components. The same blend of polyamide/styrene-acrylonitrile copolymer developed phase morphology where PA6 is the matrix when processed using a single-screw extruder, whereas the inverse situahon occurred when the blend was mixed several times in a laboratory mixer. 

Vainio, T. P. and Seppala, J. V., The effect of mixer type and processing conditions on the morphology of polyamide polypropylene blend, Polym. Polym. Compos. 1 421 (1993). 

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