Grab Your Lab Coat! – Preparing The Polymer Solution

The initial batch of reagents arrived – I was quick to don my lab coat and get mixing :-)
But first a little about the chemistry of the whole process…

Chemistry

Referring to a paper by Joseph Muskin, Matthew Ragusa and Thomas Gelsthorpe, titled “Three-Dimensional Printing Using a Photoinitiated Polymer” they outline a similar reaction very well and also demonstrate a rudimentary projector printing technique. So a directed thanks to them.

UV Laser Initiated Polymerisation

UV Laser Initiated Polymerisation

The composition of my solution contains:

  • Poly (Ethylene Glycol-400) Diacrylate
  • Phenylbis (2,4,6 Trimethylbenzoyl) Phosphine Oxide
  • Bromothymol Blue Dye

UV light incident upon the photo-initiator (Phenylbis (2,4,6 Trimethylbenzoyl) Phosphine Oxide) is absorbed and free radical species are generated.

The generated species then react with the Diacrylate monomer to initiate polymerisation.

 

 

 

Dyes

The selected dye was “Bromothymol Blue” chosen for two reasons:

Varying pH Colours

Varying pH Colours of Bromothymol Blue

  1. Acceptable level of light absorbance circa 405nm.
  2. The colour of Bromothymol Blue dye solutions are highly pH dependant, giving some degree of colour control of the produced parts. In acidic solutions, the dye is bright yellow; neutral solutions (pH 7) the dye is green, and in bases is a deep blue.
    The polymer solution is mildly acidic, giving a nice yellow colour to parts. Therefore an aim will be to investigate the necessary amounts of a base (such as NaOH) required to be added to the polymer solution to generate these three different possible colours for part production. It is straightforward to calculate the required amount of a base to be added, however I will revisit this at a later date as it is not a primary goal.

Bromothymol Blue Dye Absorption Spectra

Bromothymol Blue Dye Absorption Spectra

Preparation

Preparation Of Initial Polymer Solution

Preparation Of Initial Polymer Solution

The initial batch produced will be based upon the Muskin et. al formula of 98ml of monomer with 2g of photo-initator.

The solubility of the photo-initiator in the diacrylate is poor, although 2g does eventually dissolve. If I find myself making batches more frequently, I will invest in a magnetic stirrer to speed up the process!

All forms of the polymer solution are stored in amber glass bottles to prevent ambient UV light spoiling the solution.

Initial tests show the prepared solution works well, and early results are very promising. Processing times appear very fast with the current laser prototype. In the coming weeks this will be quantitatively assessed, and a decision made as to wether or not to proceed with the planned upgraded laser design (which would be approximately double the laser power).

Further work: Experiment with dye concentration effect upon slice thickness achieved under standard conditions; and to investigate slight pH changes for creation of yellow, green and blue useable polymer solutions.

Thursday, June 9th, 2011 Chemicals

7 Comments to Grab Your Lab Coat! – Preparing The Polymer Solution

  • melka says:

    Hi
    I just found this blog and I’m glad I caught it in it’s infancy :)
    I’m wondering what kind of laser you plan on using ? I read here (http://www.scribd.com/doc/51619344/Manufacturing-Processes) that old 3D Systems machines used a 320-370nm wavelength but I guess that’s dependent of the resin used.
    Cheers and good luck

    • Daniel says:

      Thanks,
      The most common type of laser used in this process is a solid state frequency tripled Nd:YAG laser (THG) at 355nm, however in order to simplify and compact the unit, I have decided to go for a diode based setup around 405nm.
      Only the other day, I successfully managed to initiate polymerisation at this wavelength, which was a major concern of mine at such a longer wavelength, so we are still on track. :)
      The laser head and scanning system is nearly complete, so expect a post on this by the end of the week if all goes well.
      Cheers.

      • Victor says:

        Daniel, how’s the progress? There are many commercial efforts in Photolithography printing, e.g. Form 1, but they are still beyond my financial reach.

        Tell me, did you consider using polygon mirror like in a laser printer instead of galvos (or at least, one galvo)?

        Good luck in your impressive effort, I use your site as a guide in the area.

  • melka says:

    Hi Daniel
    Thanks for the infos, I’m really looking forward to the next posts :)

  • Khoa says:

    Daniel, I just read the paper you’ve linked in the post on three dimensional printing and it outlines “projection microstereolithography” which is essentially what I am hoping to accomplish. I was wondering why you were going the laser route?

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