Question

Thixotropic Index

How I could lower the thixotropic index of vinyl acetate homopolymer obtained by emulsion polymerization using only polyvinyl alcohol partially hydrolyzed without surfactant and ammonium persulfate as an initiator?

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  • Durgadas Bolikal · Rutgers, The State University of New Jersey
    Hi Juan,
    I don't have an answer for you. But thanks to your posting, now I know what Thixotropic Index is. I am sure one of the members will know the answer. Good luck.
    Have great weekend
  • Miguel Segundo · Federal University of Pernambuco
    Dear Juan I don't have an answer for you too. But I have an article in portuguese. Do you reading in portuguese? If you reading I sent for you. See u!!!
  • Juan Herrera Reséndiz · A P Resinas S.A. de C.V.
    could you send me the article? Please, thanks Miguel Segundo.
  • Juan Herrera Reséndiz · A P Resinas S.A. de C.V.
    your welcome Durgadas Bolikal, is important this rheological property, for the final application in adhesives. have a great weekend
  • Pierre Tanguay · Working in industrial chemical R&D full time.
    Hello Juan? I was reading the various topics discussed in my preferred groups on this website, and saw yours.

    1st) I am a formulator and did worked as the senior formulator for a mid-size coatings (Paint) company some ~ 12 years back. Maybe closer to 15 years ago. (During some 8 years even though I already had previous experience in coatings).

    Anyhow, just wanted to tell you that since you "Final" ready to sell product is highly thixotropic according to you, for the least, I may point out that I remember very well that synergism (Separation) of latexes is a criteria as one needs to evaluate which latex should become the "Workhorse" within the company he works for.
    Therefore, if you claim that your emulsion is sort of pretty much thixotropic (Pseudoplastic rheology behavior), it ain't that much of a bad considering its resistance to synergism, Hum?

    I seen pretty much thixotropic latexes before... And how do you determine you thix index? On a "Brookfiekd" viscometer or you use the Casson fitted curve? What's the thix index you obtained?
    Does your latex "Creams", higher micelle concentration on the surface of the bulk?

    The thing is this: => It is ultimately the responsibility of the formulator, the end user who buys and process your latex into consumer goods, to add proper surfactants in order to reach a good application for the consumers.

    Moreover, let me take for granted that you already know of latex forms a film?
    In an older concept, the use of a so-called "Coalescing Aid"?
    Fusing the micelles together once the water is evaporated.
    Provided that the glass transition of the polymeric plastic has a viable "Tg".

    Once this is known, one needs to also take in consideration that the addition of surfactants to a given coating formulation will (Always) change the latex's Tg. Look into proper literature and you'll find this well known and recognized fact.

    In short: What type of latex you want to produce? For what type of application is it intended?
    It could happens that I'd be interested into a very thixotropic latex for sort of water based tile peelable film applied onto the walls of expensive automotive paint rooms that needs to be rid of oversprays every months?
    In such a water based formulation, a formulator needs to consider the price of a special non-ionic associative rheology modifier such as "BYK-425" from "Evonik", the lowest dosage of B-425 I need to use to obtain a formulation that offer a "High Film Build" thickness for a given latex, the better my boss loves me!
    AND! My boss is a nice women. I like that, Ok?

    Alternatively, in the extreme contrary, an ideal "Leveling" from water based self-crosslinkable latex though the use of the new industrial polycarbodimides intended as an industrial antirust paint?

    Well in such cases, I'd take a bit of an "acetoxy capped ethoxylated polydimethylsiloxane" known under the tradename "Silsurf A008-AC-UP ®" produced by Siltech Canada which is poorly soluble in water but doubled (Couppled they'd say)...
    [more]
  • Juan Herrera Reséndiz · A P Resinas S.A. de C.V.
    Thanks Pierre for your comments. The thixotropic index is measured at a temperature of 25 or 30°C in a Brookfield viscometer at two speeds, one to 2rpm and another at 20 rpm, the index is the product of dividing the viscosity at 2rpm / 20rpm. Emulsion (o/w) homopolymerization of vinyl acetate with 40% solids with Tg of 40 ° C gives us the end of the polymerization with a 99% conversion a thixotropic index of 3.6, but at present we lose their value and 1.4 (1.5 required the client). the final application is for wood adhesive. I thank all of your comments and we communicate through this medium. thank you very much :-)
  • Pierre Tanguay · Working in industrial chemical R&D full time.
    Oh oh! Juan... I see that you sure know what you are talking about when I read your reply.
    You took 2 RPM speed with a factor of 10... This is the righ way, as long as the same lecture can be repeated a few times. But considering that it is a latex, not very viscous, I guess it's fine.

    You also mentioned in your last reply that the end-use product is a wood adhesive...
    Which is not a "Wood coating" from what I read...
    And a latex baring a thix index of 3.6 for the end product is a little high for the end product.
    Just by reading it's technical data sheet, I wouldn't order a sample to formulate it.

    You know what? I had in mind : - Is it the direct "Dial Reading" numbers at speeds of 2 RPM & 20 RPM, you are dividing to get the 3.6 thix index? I know, my question is silly but only want to make sure...

    Bottom line, you state that it is the lost of thix index once the latex stablized itself after a while, isn't it?
    Well, I'll tell you that everywhere I worked I always needed to be "Practical" in every circumstances cause in the end, we have to earn our living, Hum?...

    I'm pretty sure that anywhere all over Europe, anyone can have access to samples of, as well as to 200 litres drums of the Evonik rheology modifier named "Byk 425". At 40% solids (W/W) I guess, BYK-425 is bound to bring up the thix where you want it be (1.5 to 1.6) and even more if you feel like it.

    By the way, in many instances, it takes less, much less than 1% (W/W) on total formulation weight.
    Also, when you'll read BYK-425 technical data sheet, take good note that its molecular structure is an associative polyurea rather short polymer.
    I can tell you that it doesn't detract the gloss of any given coating or binder formulation.
    As well, it doesn't cause any prejudice to the water resistance of the formulation you're working on.
    You may see a slight, so very slight reduction of the Tg of your your latex if you wear special "Superman" glasses.

    All other rheology modifiers that could help your stabilise your thix index induce other problems.

    Speaking of an homopolymer vinyl acetate, Juan...
    You're telling us 40% solids?......
    Humm... Should I comment?
    Anyhow, I tell you that we buy one at 62%, Tg of 30C.
    An "Oldy", polymerised in presence of hydroxyethyl cellulose. Very cheap...
    For our peelable film for automotive paint rooms.

    I guess that : -"To each application, goes its raw materials"?
    Who said this historical proverb? ....I forgot.

    Pierre.

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