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Performance of PP polypropylene extruder foaming system

data:2019-9-14
 
Performance of PP polypropylene extruder foaming system
1.1 Viscoelasticity of polypropylene melt
During the bubble growth stage of PP extrusion foaming, the PP melt forming the bubble wall is subjected to biaxial stretching, and the PP combustion body undergoes intense techniques.
Stretching deformation, so the viscoelasticity of the polypropylene explosive body is stable to the growth of the bubble, the uniformity of the cell size, the collapse of the bubble, and the crack
Whether or not, the expansion ratio will eventually have an important effect on the performance of the foamed product. In the initial stage of bubble length, polypropylene is required.
The tensile viscosity of the olefin melt is low to allow the bubble to grow rapidly; in the subsequent growth process, the stretched pig must be increased.
To a high enough level to keep the growth of the bubble stable, if the tensile viscosity of the melt decreases at this time, the stretch has changed
The bubble wall of the book will become thinner under the action of internal pressure, and the bubble will easily collapse, affecting the uniformity of the bubble size and the foaming of the product.
Magnification. If the tensile viscosity of the melt increases at this time, the deformation of the thinner bubble wall will decrease as the viscosity increases with the force.
A product having a uniform cell size and a large expansion ratio is obtained. In addition, at the final stage of bubble growth, at high tensile rates
The melt elasticity of the PP should be high enough to prevent the bubbles from exploding and promote the closed-cell bubble structure. Therefore PP melt is at different temperatures
And the tensile viscosity and melt elasticity at strain rate are the key in polypropylene extrusion foaming, too low blocking viscosity and melt zenness will
The window for extruding the PP is narrowed, and the stable growth of the bubbles cannot be controlled, and a high-quality foamed material is obtained.
-• At a constant temperature and strain rate, the phenomenon that the tensile viscosity of a flame increases rapidly with time or stress is called strain hardening.
Also known as tacky; melt elasticity, industrially characterized by flame strength and extrusion swell, which is commonly used in extrusion foaming
Melt strength, which is the tensile force (at a certain temperature) when the extruded spline is stretched at the maximum stretching rate. The general PP melt is pulled.
The tensile viscosity during stretching does not show strain hardening, and the elasticity (melt strength) of the melt is very low, resulting in general PP
The hair expandability is poor, and the processing window suitable for extrusion foaming is narrow. Therefore, how to improve the expandability of polypropylene for a long time, that is,
Improving the viscosity and elasticity of the general PP part and broadening the processing window of PP extrusion foaming must be solved for the development of PP foaming materials.
A key technology.
To date, the main techniques for improving the viscoelastic properties of general-purpose polypropylene melts include: (1) increasing the relative molecular mass; and (2) broadening the phase.
Molecular mass; (3) blending with other branched polymers; (4) grafting long chain branches on the universal polypropylene linear backbone to obtain long
Chain branched polypropylene; (5) Universal linear polypropylene blended with long chain branched polypropylene. These methods are used to stretch the polymer melt
The effects of viscosity and melt elasticity are different: among them, increasing the relative molecular mass and broadening the relative molecular mass distribution can improve the melting.
Body strength, but the increase in melt viscosity is not significant; and the introduction of long branches on the universal polypropylene linear backbone gives long
Chain-branched polypropylene can simultaneously increase tensile strength and melt elasticity, and long-chain branched polypropylene has significant strain hardening.
And higher melt strength.
Before the 1990s, researchers mostly changed the rheological properties of polypropylene by cross-linking and blending with other polymers.
Improve the melt elasticity of PP. Cross-linking includes fu-crosslinking and peroxide cross-linking, but the degree of cross-linking is difficult to control, and
The presence of gels affects recycling, and cross-linking is not a good technique. And blended with other branched polymers
Sex technology such as blending with LDPE, in order to obtain suitable carcass strength, the amount of other resin added even exceeds the matrix tree
Lipopolypropylene cannot fully utilize the advantages of polypropylene. Therefore, since the 1990s, it can be used for polypropylene.
The focus of research has shifted to the development of long-chain branched polypropylene, the most researched and commercially available technology in this field.

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