The following XRD graph is given by natural rubber clay composite. Mechanical properties of the sample is good. ( higher modulus and tensile strength). Higher strain induce crystallization is also visible in stress strain curve. Has any other method to confirm that crystalline structure to be checked or calculate the degree of crystallinity ?
Did I get this right? You measured from 2Theta=2°-10°?
If yes, you cannot say anything useful with respect to crystallinity, as most polymers show their main crystalline peaks around 20°. If you repeat the experiment in 2Theta=10°-50° or larger, it would be more useful.
Did you try DSC? The x0 and Tm0 of natural rubber should be known. All you need to do is to normalize by the polymer content of your sample.
Thank you sir. I will try for that range too. I didn't use DSC because melting point of amorphous polymer is difficult to find. Crystallinity develops in the sample while it is stretched due to strain crystallization. if it has a method to determine crystalinity at higher elongation, then my attempt would be success. I want to check how much crystalline structure in the original sample and how much it develops while stretching.
Natural rubber is composed of close to 100% cis-polyisoprene structure, its counterpart, the synthetic polyisoprene rubber has around 90% -cis content while chloroprene rubber has around 92% -trans content. As a result, all these three show a good amount of stress induced crystallinity. However, some factors like short side branches, bulky groups in the main chain, and rigid structures are found to be hindering the crystallinity and thereby significantly reducing the tendency to crystallize under external stress.
A crystalline state is characterized by a regularly ordered array of units that are held together by strong intermolecular forces with associated high mechanical properties. They can resist external stress in a better way and hence these rubbers are often ‘self-reinforcing’. This is exactly the reason why natural rubber and chloroprene rubber vulcanisates often exhibit a series of properties even in their gum state, unlike other rubbers.
Thank you Mr Sasidharan. Can strain induce crystallization be improved by incorporation of layered particles such as clay ?
Due to the nanoclay platelet-like structure presenting a high aspect ratio and propensity to accelerate polymer crystallization, nanocomposites with these clays show enhanced mechanical properties, improved solvent resistance, high thermal stability, and, usually, reduced permeability.
I have done with Cloisite 93A.( Refer RCT)
First of all amorphous polymers do not have a melting point (by definition), they only have a glass transition.
Unless you have a possibility to determine XRD in stretched state (you have to essentially combine the mechanical tester and the XRD), you can only test offline. If you can not do such a test, the sample will partially relax the strain you induce and that might also reduce the strain-induced crystallinity and will definitely affect the crystal structure. So (off-line) XRD and DSC will both show you a state different from the one you want to test. Telling how much this relaxed state actually differs from the online state is not straightforward, as it highly depends on the material and strain history used.
It is possible to evaluate the degree of crystallinity for rubber composites following the methods recommended in this article:
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000701491
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Powders