Abstract
AbstractScratch‐resistant coatings for bisphenol‐A polycarbonate sheets were obtained by the sol–gel synthesis of an organic–inorganic hybrid system based on poly(ethylene oxide) and silica. The organic–inorganic hybrids were thermally cured into hard transparent coatings by using conventional and microwave (MW) ovens. Both techniques proved to be equally efficient in promoting the system's crosslinking, as evaluated by 29Si MAS‐NMR. The MW‐assisted curing, however, was much faster. Photoelasticity analysis showed that MW‐assisted curing causes localized overheating of the samples, inducing a state of residual plane stresses that bring about dimensional instability of the coated material. Instrumented scratch tests for the coated samples revealed an increase of 1 order of magnitude in the minimal load at which a scratch track appears on the sample surface. However, the friction coefficient values for samples with thermally cured coatings were lower than those produced by MW‐assisted curing. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:117–126, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20122
Highlights
The poor wear and scratch resistance typical of transparent polymeric materials such as polycarbonates often represents their main limiting factor in all those applications in which the contact with dust or abrasive agents cannot be avoided
The performance of a coating layer to protect the substrate from scratch damages strongly depends on the intrinsic properties of the coating material, such as its chemical composition, and coating film properties such as thickness, hardness, and adhesion to the substrate
These latter features, in the case of sol–gel-derived organic–inorganic hybrids, can be tuned to a large extent by a judicious choice of chemical precursors in the recipe, the amounts used, and the way in which they are cured into a permanent hard coating
Summary
The poor wear and scratch resistance typical of transparent polymeric materials such as polycarbonates often represents their main limiting factor in all those applications in which the contact with dust or abrasive agents cannot be avoided. While it is well known that in general the abrasion resistance of a material can be correlated to its surface hardness,[20] for organic–inorganic hybrid materials, the latter can be further linked to the crosslinking density reached by means of postcuring treatments.[15,21,22] For this reason, 29Si MAS-NMR represents a useful tool for a direct comparison of the effectiveness of thermal and MW-assisted curing of organic–inorganic hybrid materials.
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