【JST-035】Polymer One-on-One Mutual Assistance Office
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This post was last edited by Firefly on 2015-4-10 08:29. Technical discussant: arclie001; Field of expertise: Polymers. My area of specialization is polypropylene. Time spent online daily or weekly: 1–2 hours per day, from Monday to Sunday. Work experience: Over 18 years. PS: The field of polymers is very broad; it’s impossible for me to know everything, so I hope to learn and improve together with everyone else
Is it in terms of production technology or application technology?
Regarding PP, there are no issues with production or application; as for the other aspects, it mainly comes down to application, and everyone should discuss together ways to improve it
1 Why does the melt index increase after the load on the extruder is reduced? Has degradation occurred or what? ? Secondly, generally, after the powder material passes through the extruder, its melt index decreases; what kind of reactions take place in the mixer?//
This post was last edited by arclie001 on 2013-5-17 08:55. Let’s answer the later questions first. Generally, during mixing in an extruder, the molecular chains are broken, and the melt index should increase; however, in most domestic manufacturers this value actually decreases. The main reason for this is that antioxidants act as nucleating agents in this process, leading to increased crystallization and a consequent decrease in the apparent melt index. Returning to the previous question, regardless of whether the extruder is under high or low load, the apparent melt index should change in the same way – that is, it should decrease under high load and also decrease under low load. If the melt index increases in your case, it’s likely due to a change in the proportion of additives; please check the weighing system.
Many people combine polymers with rubber, feeling that the two have many similarities or even are equivalent to each other. Could you explain the differences and connections between the two in a simple yet detailed way? Thank you!
The three major synthetic polymer materials are plastics, rubber, and fibers; rubber is just one of them. Rubber is a polymer with a glass transition temperature below room temperature, which exhibits high elasticity at ambient temperatures.
I’ve been quite busy these days and haven’t had time to look into it. The company provides 7 methods in its training materials for improving the flow index: reducing the temperature and pressure of the molten resin, increasing the opening degree of the throttle valve, using a smaller number of screens, increasing the amount of additives used, reducing the speed of the extruder, and increasing the output capacity of the extruder. I don’t understand these methods; I hope the original poster can provide an explanation from a theoretical perspective. Also, every time the load is reduced, the index does increase, and the amount of additives fed in remains normal – I’m not sure why
This post was last edited by arclie001 on 2013-5-22 at 11:25. Simply put, it is the increased mixing intensity that leads to more breaks in the molecular chains, thereby raising the melt index. Theoretically, then, increasing the temperature and pressure while reducing the addition amount should increase the melt index. As for reducing the load, this means lowering the speed of the extruder; this in turn prolongs the mixing time. To a certain extent, this increases the mixing intensity and thus raises the melt index. However, such an increase is limited and there are constraints (it is not possible to reduce the speed indefinitely).
Polyoxymethylene is a linear polymer with no side chains, characterized by high density and high crystallinity. It possesses excellent mechanical properties, as well as good electrical insulation, solvent resistance, and processability. It is one of the five most common engineering plastics, and is commonly referred to as \"super steel\". It is mainly used to replace some markets traditionally occupied by metals, such as replacing zinc, brass, aluminum, and steel in the production of many components. Polyoxymethylene is a thermoplastic material, and it possesses the highest rigidity among thermoplastics. It maintains good creep resistance, geometric stability, and impact resistance even at low temperatures; the main consideration when using it is its somewhat poor thermal stability.