PP-PC, PP-PE, PP-ABN, PP-HDPE, PP-Metal blending are generally immiscible,on the other hand HDPE and LDPE are miscible. What causes them miscible?
Hi, polymers are generally poorly miscible. The reason is their high molecular weight which lowers the entropy of mixing. The enthalpy contribution to the Gibbs free energy of mixing then outweighs this. Search for the Flory-Huggins equation; it is included in almost any standard textbook for polymer physical chemistry.
That said, it is unsurprising that PP is not miscible with other polymers. LDPE and HDPE are two types of polyethylene, so yes, polyethylene is miscible with itself.
It is well known that polymer-polymer blending or solubility is usually poor. For small molecules entropy can drive solubility but it is negligible for polymer mixing. So polymer miscibility must be driven by enthalpy - the interaction between polymer 1 and polymer 2 must have a negative delta H.
HDPE and LDPE are so similar that they can be made to blend. The only difference is in the greater branching of LDPE.
it has been reported that deuterated PE and regular PE (hydrogen instead of deuterium) do not blend - that even this most minuscule of chemical differences still results in segregation into deuterated and hydrogenated domains.
Dear James,
True answer.
This is true miscibility influence the thermal stability. As of now, I know enthalpy either can increase or decrease DeltaGm. According to dipolar physics, there is a quite difference enthalpy stability values between liquid liquid mixing and solid solid mixing, for example alloy-alloy binary system enthalpy formation closes to zero. Transition to immiscibility is largely affected by dipolar physics, + plus system indicates the immiscible system and - (minus) system for negative enthalpy for miscibility is exothermic
Dear Petr,
You are true.
Very true answer. What I understand , atomic size difference encourages enthalpy of mixing. Dilution is generally a process evolving negative enthalpy change and mixing occurs when the free energy is less than its ideal value. Perhaps this indirects the miscibility and immiscibility condition. polymer blending is mostly non fusible dilution, however crystallinity of HDPE is higher than LDPE(highly branched) staking neatly preventing the chain but being a same family group both are forcefully blended( highly permeable at a temperature) at almost same melting point.
Ashish
Readers can give their important technical view on the query beneficial for polymer science in health of academia and industry as well. They can correlate the multi concept interlaying with polymer, physics, chemistry, science and technology.
If blending similar M. Weight polymers, the main reason of incompatibility is that some of the Polymers mentioned are crystalline and others are amorphous; the addition of rubbers like EPDM will improve properties.
Dear Emilio,
Thank you very much for your technical review on questionnaire.
Ashish
Put it in short, like disoolves like and both HDPE and LDPE are made of (P)E repeating units in short range, so they get mixed, or rather two PE compunds with different average atomic mass and chain braching averages themselves out. Such is not the case for any polymer pairs yoy mentioned.
Dear Sumit,
Your answer may be true.
Though, crystallinity of HDPE is higher than LDPE. But they fall in the same group compound in one important feature, but what I understand enthalpy changes and mixing occurs when the free energy is less than its ideal enthalpy value.
Ashish
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