If we see a sudden deformation and compression of the polymer, we will see a local increase in the density of the system and the energy deposited into the polymer by performing mechanical work on it may as well lead to a small temperature spike (assuming the following and with the magnitude of this spike being dependent on the following as well: that the polymer is "stiff", that the deformation is very rapid and that the polymer conducts heat rather poorly).
Such conditions may be sufficient to trigger a solid state reaction between any free and reactive groups present in the polymer. If those groups react and yield a "bridge", then you will see an increase in cross-linking dnesity. I would, however, expect the magnitude of the effect to be rather low (if not negligible) and achieving a significant increase in cross-linking density would both require the polymer to be rich in such cross-linkable groups and possibly long-term compression/decompression cycling.
Can you suggest some related papers/published papers on this matter ?
Crosslinked polymers are formed only when monomers taking part in polymerization are polyfunctional means having bonding sites which may be in the form of functional groups or degree of unsaturation like double and triple bonds. Polyfunctionality of monomers is a prerequisite for crosslinking. Compression will not be reflected upon increase in crosslinking density. It may bring about just compaction of the polymer due to compressive load. No increase even due to decompression either.
@ Aviru Kumar Basu
Off the top of my head, DOI number: 10.1080/05698198308981519
Please take note that relatively harsh mechanical stimulation was used in the work and we would not expect to see as much of an effect in a short-term experiment.
@ Shrikaant Kulkarni
I agree with you on the matter of functionality, however, we would need to assume that all of the functional groups of the monomers have taken part in the polymerisation reaction. This is usually not the case, for a multitude of reasons and the "leftover", unreacted functional groups may take part in follow-up, post-polymerisation reactions. If we locally compress the polymer and, therefore, reorganise its microstructure, with a sufficiently high concentration of these groups and assuming that the conditions are sufficient to induce a reaction between them, we can observe a "second" polymerisation of these unreacted groups, resultin in an increase of cross-linking density.
Dear Dr.Tomasz Jarosz,
I shall be grateful if you kindly provide a reference which shows the effect of plastic strain (i.e. permanent deformation) of polymers on the cross-linking network density.
Regards
Aviru
In addition to involving unreacted functional groups in the cross-linking there is one more option - scission of the macromolecules under the applied mechanical loading. This possibility depends on the polymer nature and rigidity as well as on the mechanical force value, rate of its application and degree of the plastic deformation. This possibility can be checked by Electron paramagnetic resonance (EPR, ESR) measurements of the freshly deformed materials. Lowered temperatures (freezing) can be used to prolong life of the formed free radicals on the broken chains.
I shall be grateful if you kindly provide a reference which shows the effect of plastic strain (i.e. permanent deformation) of polymers on the cross-linking network density.
Regards
Aviru
@ Tomasz Jarosz
With a given stoichiometry between the monomers and processing conditions the polymerization reaction should go to almost to its logical end. The leftover functional groups may come into being if any of the monomers is like a limiting reagent or process conditions are not maintained till the completion of reaction or adequate stoichometric ratio is not maintained. Normally crosslinked polymers once set on curing become dead polymers which are stable thermodynamically. You mean we can reactivate them during post polymerization because of leftover functional groups and on subjecting polymers locally with the mechanical force. Will it bring about any reasonable change in the crosslinking density in the aftermath of the polymerization.At times crosslinked polymers are formed when monomers have polar functional groups in preference. I don't think there should be any change in crosslinking density to reckon with once polymer gets cured.
Article Effect of the molecular network on high-strain compression o...
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