Dear everyone,
I tried to prepare Poly lactic acid (PLA) and Polybutylene adipate terephthalate (PBAT) blend. PLA and PBAT resins were mixed together(PLA=800g and PBAT = 17,500 g). Twin screw extruder was used to prepare the resins of the blend. However, when the melt (PLA/PBAT blend) comes out of the die, it breaks after some time before cooling (water cooling). The melt as it comes out of die becomes thicker or thinnner (at one side) and breaks.
If anyone could explain me this situation? if it is a problem with the mixing ratio or any other problem? The temperature of the twin screw was not more than 190oC in all cells.
Thankyou
Dear Manish Pokhrel, what about the compatibility of this binary polymer blend? I think this is due essentially to phase separation once the melt exits the die and starts to cool down. My Regards
Thankyou so much Abdelkader BOUAZIZ .... I am quite new to this area and I will try again using a compatibilizer. However, are there any other reasons that might create such scenario, for instance, due to high cutting speed of the pellets or issue with temperautre etc.?
No thanks, other thing to consider is the melting temperatures of both polymers and the processing one. My Regards
The blend breaks because the material of die (metal) and blend have different Coefficients of Thermal Expansion.
Dear all, I add also the phenomena of melt instabilities such as 'shark skin' and others, which indicate the relaxation of imposed stresses during extrusion. So by this I mean do both polymers have similar or close processing conditions? My Regards
It depends on the extrusion parameters. Sometimes one of the co-extruded components is pushed into the outer (near-wall) layer.
Thankyou Abdelkader BOUAZIZ and Leonid V Vladimirov for the responses
Hi. May I know what do you means by break? Does the blend still has visible of 2 different phases during the break?
Faizall Mohd.... the melt when it comes out of the extruder becomes thick and gets separated from the bulk. I cannot put it exactly but it is similar to drops of water which falls drop by drop.
I'm sorry that I'm not familiar on using PLA or PBAT, either of it's blend.Strictly in my opinion, however, if you consider the structure of these both polymer, double bond oxygen from both side of the polymers might be the issue. Dipole moment of the oxygen bond may cause the polymer to be polar, and with same polarity from PLA and PBAT, it repelling each other, create incompatibility. From my experience, to extrude this kind of polymer, temperature parameter is critical to control any oxidation occured and make it worst. Do these both polymer have special compatibilizer in any literature?
Dear Manish,
Some polymer blends are brittle because the co-continuous phase structure is incomplete.
I have attached some articles about the mentioned problem about PLA and PBAT blend. I hope they would be useful.
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