To be more precise, starting from a 50% resole in methanol, I want to obtain some highly resistant laminates (in terms of mechanical strength). I usually add a specific percent of hexamethylenetetramine as a curing agent before the impregnation step and everything works well. But the process doesn’t always behave as required. Sometimes, the resole raw material in some batches seems to be ’more active’ than usual and I get an impregnated material (after drying) that no longer glues to form several layers even though nothing was changed in the process. This means failure of lamination. The resin is a given, so I cannot know what changes have been made during synthesis.
Is there any way to compute the best percent of curing agent depending on the reactivity of the starting resole? Could the gel time test be useful in any way? Any other suggestions for fixing this problem?
Thank you!
Hallo Andreea-Daniela Dima ,
without any look-up or knowing your process in detail - just from a gut - I guess that using a gel-time-test is not a right solution. You have to take the temperature-time dependency into account. Maybe DSC-measurements can give you qualitative comparison for your proceeding over the process steps and batches.
The reason is more the mixing ration and the mixing quality. These also depend on further material and process parameters, e.g. viscosity, density, air inclusion. To identify this have a look on measuring systems like refractometer or NIR spectroscopy.
Kind regards
Mark
Hello Mark Opitz,
Thank you for your answer and the useful suggestions.
Best regards,
Andreea
Gel-time test only measures the time and temperature during the curing process. It does not show any chemistry. It is more like a trial-error test. You can measure how much curing agent you need as long as the temperature does not rise too high and the time for curing is logic. DSC is a better solution since it shows chemical changes and shows if the curing process finalized..
Dear Ms Alisa Buchman,
Thank you for your kind answer.
In fact, I was trying to improvise with custom laboratory equipment and very simple methods that anyone could perform, even workers in a factory.
I thought that I could use the gel time test to see if there are some differences between several batches of resin, but only in a comparative manner. Since I perform the test at the same temperature, different results should provide information that these resins act differently, although they have the same dry mass.
Let’s say that my first batch gives a result of 150s, while the second gives 180s. I would conclude that in the second case, the resin has more sites for linkage which make the reaction take longer; this could also mean a lower degree of polymerization. Consequently, for this resin I can add higher quantities of curing agent compared to the first case and somehow compensate the time needed for curing.
On the other hand, I doubt this reasoning for my little experience in working with resins, which is why I very appreciate your suggestions.
Best regards,
The chemistry of the resin curing is more complex. To understand, imagine a puzzle: For every part of the net resin you have a defined quantity of hardener (stoichiometric ratio). Using additives can change the material behaviour or reaction speed (Catalysts as accelerators). You can not speed up the reaction by adding more hardener. This ends up to uncrosslinked parts of the hardener in the component, which changes the mechanical properties. Compared to the puzzle: you have pieces over that don't belong to the picture at all.
This is a very suggestive explanation. Yet, my intention is not to add more hardener than needed (and overcome the stoichiometric ratio). In fact, I am trying to determine the stoichiometric ratio. In a simplified manner, I am working with two samples of phenol formaldehyde resin to which I add hexamethylenetetramine (HMA). Before adding any HMA, at 150 degrees, the first sample gives a gel time of 120s, while the second gives 150s. There must be a difference of reactivity or molecular mass since both have the same dry mass and viscosity. How should I determine the needed quantity of HMA for each of the sample for complete curing? I have noticed that if plotting the gel time as a function of HMA concentration in the resin, I obtain a hyperbola which flattens for high concentrations of HMA. I though that the point at which this curve tends to become linear could indicate the required quantity of HMA.
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Powders