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Reactive Diazonium-Modified Silica Fillers for High Performance Polymers Mariusz Piotr Sandomierski, Beata Strzemiecka, Mohamed Mehdi Chehimi, and Adam Voelkel Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b02891 • Publication Date (Web): 11 Oct 2016 Downloaded from http://pubs.acs.org on October 17, 2016
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Langmuir
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Reactive Diazonium-Modified Silica Fillers for High Performance Polymers
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Mariusz Sandomierski1, Beata Strzemiecka1,*, Mohamed M. Chehimi2*, Adam Voelkel1
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Poznan University of Technology, Institute of Chemical Technology and Engineering, Berdychowo 4, 60-965 Poznań, Poland
Université Paris Est, ICMPE (UMR 7182), CNRS, UPEC, 2-8 rue Henri Dunant, 94320 Thiais, France
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Abstract We describe a simple way of modification of three silica-based fillers with in situ generated 4-hydroxymethylbenzenediazonium salt (+N2-C6H4-CH2OH). The rationale for using a hydroxyl-functionalized diazonium salt is that it provides surface-functionalized fillers that can react with phenolic resins. The modification of silica by diazonium salts was assessed by FTIR and XPS. FTIR permitted to track benzene ring breathing and C-C. The absence of the characteristic N≡N stretching vibration at 2200-2300 cm−1 range indicates the loss of the diazonium group. XPS results indicate a higher C/Si atomic ratio after diazonium-modification of fillers as well as the presence of π−π* C1s satellite peaks characteristic of the surface-tethered aromatic species. Adhesion of aryl layers to silicas is excellent as they withstand harsh thermal and organic solvent treatments. Phenolic resins (used e.g. as binders in abrasive products) were filled with diazoniummodified silicas at 10 - 25 wt. %. The reactivity of the fillers towards phenolic resins was evaluated by determination of flow distance. After annealing at 180 °C, the diazoniummodified silica/phenolic resin composites were mechanically tested using the three-point flexural method. The flexural strength was found to be up to 35 % higher than that of the composites prepared without any diazonium salts. Diazonium-modified silica with surface bound –CH2-OH groups are thus ideal reactive filler for phenolic resins. Such filler ensures interfacial chemical reactions with the matrix and imparts robust mechanical properties to the final composites. This specialty diazonium-modified silica will find the potential application as fillers in the composites for the abrasive industry. More generally, aryl diazonium salts are unique new series of compounds for tailoring the surface properties of fillers and tuning the physicochemical and mechanical properties of polymer composites.
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corresponding author:
[email protected] ;
[email protected] 34 35 36
Keywords: silica, aryl diazonium salt; surface modification; novolak matrix; composite interface
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1. Introduction Phenolic resins are among the most important resins used as binders for materials containing glass, wood, metal, paper, rubber and others.1 They are most often used for the production of abrasive tools as they possess very good thermal and chemical stability, high hardness and the ability to bind abrasive grains and fillers together. Abrasive articles are complex composites consisting of abrasive particles, wetting agent (most often resole), binder (most often novolak) and filler (e.g. cryolite, potassium fluoroaluminate (PAF), pyrite). 2, 3 World production of phenolic resins is more than 6 million tons per year and it is 2 % of the world production of polymers. The main factor contributing to the wide application of phenolic resins is their ability to cure by heating. 4, 5 Phenol-formaldehyde resins are divided into resoles and novolaks. The conditions required to obtain the phenol-formaldehyde resins are shown in Table 1.
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Table 1. Types of phenol-formaldehyde resins. Resin type Catalyst F/P Physical State Novolak Acidic
