I am rather an expert in plasma treatment wich may not be on your list. I believe that a company called Gelest, Inc. may have some good solution. The president, Barry Arkles, is a good expert in silicon based chemistry. I could alredy learn o lot from him just from their catalogue.

Dear Heinrich Gruenwald , thanks for your reply. I sent a massage to him and asked him to comment. Best wishes.

Dear Orkun,

Nice and complex question! Based on my experience in working with PLA, I will say that for the melt-mixing with this biopolyester, the treatment of fillers with traditional/functional silanes is remaining of first interest (e.g., aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, [3-(methacryloyloxy)propyl]trimethoxysilane, triethoxy caprylylsilane, others). On the other hand, it is important to specify that not all fillers have a beneficial effect on PLA properties. Unfortunately, the addition into PLA of some metallic compounds (e.g., MgO), ZnO, others) usually leads to the advanced degradation of PLA chains resulting in a sharp reduction of the thermo-mechanical properties of the polyester matrix. I will take as an example the case of ZnO filler known for its degrading effect at high temperature for PLA, thus it is used in the chemical recycling of PLA. To allow the processing by extrusion or by spinning (films and fibres) while limiting the thermal/chemical degradation of PLA, the treatment with about 4% triethoxy caprylylsilane was proved as being of high effectiveness (please consider our paper, Biomacromolecules 2011, 12, 5, 1762-1771).

Please consider that actually are commercialized many grades of PLA that could have different characteristics going from the molecular weights, isomer purity (L- or D-), low (amorphous structure) or increased crystallinity, and so on, thus the effects of addition of fillers (surface treated or not) can be more or less evident.

However, PLA is very sensitive to the high temperature, shearing and hydrolysis, thus all precautions should be applied to avoid its degradation. Accordingly, it is imperiously required to limit the content of water in PLA for all compositions at 50-250 ppm whatever the processing conditions, and this can be problematic in the case of some (untreated) natural fibers used as reinforcements or of fillers containing crystallization water.

Good luck in your R&D studies,

Marius

PS: Regarding the CaSO4 based fillers, for eventual interest the project TOROGYPS realized with our participation:

https://www.researchgate.net/project/TOROGYPS-DEVELOPMENTS-IN-THE-FIELD-OF-FILLERS-AND-POLYMERIC-MATERIALS-CONTAINING-GYPSUM-DERIVATIVES ) !

Dear Orkun,

For eventual help and interest some references!/Best regards, Marius

Marius Murariu, Philippe Dubois, et al., High-Performance Polylactide/ZnO Nanocomposites Designed for Films and Fibers with Special End-Use Properties, Biomacromolecules 2011, 12, 5, 1762-1771

Isothermal cold crystallization kinetics and properties of thermoformed poly(lactic acid) composites: effects of talc, calcium carbonate, cassava starch and silane coupling agents

Deetuam, C., Samthong, C., Choksriwichit, S. et al. Iran Polym J (2020). https://doi.org/10.1007/s13726-019-00778-4

Moazeni, N., et al., (2015) Study of silane treatment on poly‐lactic acid(PLA)/sepiolite nanocomposite thin films. J. Appl. Polym. Sci., 132, 41428, doi: 10.1002/app.41428

Marius Murariu, Philippe Dubois, PLA composites: From production to properties. Advanced Drug Delivery Reviews 2016, 107, 17-46. DOI: 10.1016/j.addr.2016.04.003.

M Murariu, et al, New trends in polylactide (PLA)-based materials:“Green” PLA–Calcium sulfate (nano) composites tailored with flame retardant properties, (2010) Polymer Degradation and Stability 95 (3), 374-381

M Murariu, A Da Silva Ferreira, L Bonnaud, P Dubois

Calcium sulfate as high-performance filler for polylactide (PLA) or how to recycle gypsum as by-product of lactic acid fermentation process

(2009) Composite Interfaces 16 (2-3), 65-84

Dear Marius Murariu

Judging by your answer and the literature you have proposed, it will not be easy to choose the appropriate surface agent. Some laboratory-scale trials will be required with the type of PLA and coating agents to be used. Thank you very much for your detailed answer and literature suggestions.