How to avoid pellets agglomeration issue for PBAT/PLA blends?

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Roaa Mohammed Muneer

Hello, you must first disperse the pellets with the ultrasonic device at high frequency by placing the pellets in ethanol and then using the solution in the extrusion process.

Marius Murariu

Dear Saud,

I’m not sure that I have understood 100% your approach, what are the conditions of processing and properties of PLA and PBAT that are mixed, thus I will try only to suggest some answers.

Please firstly consider the PLA and PBAT need compatibilization, and carefully selection of optimal PBAT/PLA or PLA/PBAT ratio. In fact, this it will be a function of your main goal by considering the requirements of the application.

However, for a more homogenous blend I will strongly recommend using firstly a twin-screw extruder with relatively high L/D ratio (40-50) and compatibilizers, and then to process the blend using a single screw extruder.

Please take in consideration that the L/D of a single screw extruder is small, and it will not be enough mixing & residence time to have a good blend for film blowing (a delicate technology if you can not control the rheology).

The sticking on the screw zones (feeding and compression zone) could be to some wrong processing conditions could arrive even easier in the case of amorphous PLA….Finally, follow some advice given by industrial producers of PBAT/PLA blends (e.g., BASF)!

Good luck and best regards,

Marius

For eventual help!

Best regards,

Source BASF/ Ecoflex

https://plastics-rubber.basf.com/global/en/performance_polymers/products/ecoflex.html

Li, X., Yan, X., Yang, J., Pan, H., Gao, G., Zhang, H. and Dong, L. (2018), Improvement of compatibility and mechanical properties of the poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends and films by reactive extrusion with chain extender. Polym Eng Sci, 58: 1868-1878. https://doi.org/10.1002/pen.24795

Uncompatibilized PBAT/PLA Blends: Manufacturability, Miscibility and Properties; Materials 2020, 13(21), 4897; https://doi.org/10.3390/ma13214897

https://www.mdpi.com/1996-1944/13/21/4897/pdf

A study on properties of PLA/PBAT from blown film process

P Hongdilokkul et al 2015 IOP Conf. Ser.: Mater. Sci. Eng. 87 012112

https://iopscience.iop.org/article/10.1088/1757-899X/87/1/012112

Saud Khalid

Thanks for your suggestion. I have not tried this approach. Will try it, and let you know the outcome.

Thanks for your detailed feedback, and for recommending relevant articles.

I mixed the PBAT/PLA blends in twin screw extruder (L/D: 40), and cooled the strand in water bath, before granulation. However, I didn't dry the pellets properly before running in film blowing machine (moisture content before drying: 2.56%). The pellets started to agglomerate at high temperature, and could not enter screw barrel of film blowing machine (image of agglomerated pellets is enclosed).

I made another attempt to run the pellets in the film blowing machine after drying the pellets (moisture after drying: 0.85%). Furthermore, I added CaCO3 and chain extender in the blend.

I don't know which factor helped, but I can now run the pellets in single screw extruder to make film.

Thanks again for your suggestions!

I am just curious if it is nucleating agent (CaCO3) or final moisture content that helped in resolving pellets agglomeration issue!

Would highly appreciate your feedback in this regard!

It is nice to know that you are in progress with your R&D works, thank you also for the additional information shared with us! Please note that some biopolyesters such as PLA are very sensitive to the degradation due to presence of water (the drying is absolutely required to have finally

Dear @Marius,

Quick question: Is it ok to cool the PBAT/PLA strand in water bath (after the strand comes out from the die, but before granulation); incase I don't have the conveyor belt in lab? Will it affect the performance of final blend in anyway?

Thanks for your response!

Saud

Point of view industrial production, the cooling of polymeric strands using a water bath is preferred because can allow higher productivity,. In fact, the water is a very effective cooling agent. Based on my experience, I will say that is not any problem if you do not have a conveyor belt in your laboratory (NB: I will refrain some comments regarding the effects of quick cooling on PLA crystallinity!). Please take only in consideration that using the cooling with water, your granules will have some superficial moisture, thus I will firmly recommend drying the polymer compound before the extrusion of films (e.g. drying overnight at 60-70°C).

Good luck in your research and best regards,

Fabio Caixeta Nunes

Dear all,

I recommend using some commercial coupling agent, such as Polybond 3039.

In our paper, we investigated this point.

Good luck and best regards!

Article PBAT/PLA/cellulose nanocrystals biocomposites compatibilized...

Emerson Oliveira da Silva

If I understand correctly, you already mixed the two polymers and obtained the pellets of that blend. Your problem is how to avoid the agglomeration of the pellets of the blend. I think you need to dry properly the pellets before feeding the film blow machine.

For your answers, you have already tried using dry pellets. It's worked! But, you add CaCO3, too. I think as CaCO3 is a descant, it acted on maintenance of low moisture.

I think your solution is to dry the pellets only.