We are actually working on the polyurea composites for spray-coatings. Is there any possibility of significant improvement of the hardness by application of the particle shaped filler which will not strongly influence the curing process?
Dear Mateusz, unfortunately I am not expert to answer properly. Since you have a coating to be developed I would suggest a platelet type of particle which can be aligned in plane and this way, you may get the hardness you are looking for in the normal direction. Obviously good adhesion with the matrix is a crucial factor.
Unfortunately there is not a very simple answer. The shape (aspect ratio), size, concentration, and hardness of the filler and of the matrix are important. Interface and in particular the adhesion between filler and matrix may be extremely important as well as the quality f the dispersion for the nanofiller.
Keep in mind that any property we speak of in filled polymer systems is always in reference to some kind of physical property test. Thus we are speaking in relative rather than absolute terms.
Short answer: no filler will alter the fundamental behavior of a polymeric system, unless it actually participates in the curing process. Instead, fillers can be selected to alter measured properties that we consider related to the abstract concept of hardness. Some examples:
- Hardness is commonly described in terms of compression resistance: e.g. diamond print resistance under load (Knoop hardness)
- crushing resistance (mho for minerals)
- abrasion resistance (e.g. Tabor; abrasive scrub)
- burnish resistance (polishing; gloss change)
The contribution of a given filler to results depends largely on the properties of the filler itself. For example, aluminum oxide (quite hard) is an excellent filler for increasing the abrasion resistance of a filled system, while clay is not (too soft).
The shape and size of the filler and the loading of that filler account for the balance of property contribution of a given filler. Thus fumed silicas (100 A or so) are useful for increasing the mar resistance of urethanes at quite low loadings, while larger Al2O3 particles (half micron and up) require fairly high loadings to suppress abrasive scrub processes.
Then there is the specific polymer-filler bonding that comes into play. If strong, applied loads will be transmitted to the filler matrix. If weak, fillers will act as pseudo voids, deflecting the load around them. The latter are useful for increasing impact resistance, by promoting diverse crazing in the polymer matrix, thereby blunting primary cracks forming in the polymer.
Think of it this way: when subjecting a polymer matrix to some kind of loading, it will only resist that loading if it can somehow transfer that applied load to the filler matrix contained in the polymer.
Thus, you will need to specify what measures of hardness are of interest to you so I can be more specific in further suggestions.
Regards,
Lou Floyd
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Coating