Preparation, characterization, and properties of novolac‐type phenolic/SiO₂ hybrid organic–inorganic nanocomposite materials by sol–gel method

Abstract

This article describes the preparation of novolac-type phenolic resin/silica hybrid organic-inorganic nanocomposite, with a sol-gel process. The coupling agent was used to improve the interface between the organic and inorganic phases. The effect of the structure of the nanocomposite on its physical and chemical properties is discussed. The coupling agent reacts with the resin to form covalent bonds. The structure of the modified hybrid nanocomposites was identified with a Fourier transform infrared spectroscope. The silica network was characterized by nuclear magnetic resonance imaging ( 29 Si NMR). Results revealed that Q 4 (tetrasubstituted) and T 3 (trisubstituted) are the dominant microstructures. The size of the silica in the phenolic resin was characterized with a scanning electron microscope. The size of the particles of inorganic silica in the modified system was less than 100 nm. The nanocomposite exhibited good transparency. Moreover, the thermal and mechanical properties exhibited significant improvement. The modified hybrid composite exhibited favorable thermal properties. The temperature at which a weight loss of 5% occurred increased from 281 to 350°C. The flexural strength increased by 6 -30%. The limiting oxygen index of the nanocomposite reached 37, and the Underwriters Laboratory test was 94V-0. Consequently, these materials possess excellent flame-retardant properties.

Modification of a Phenolic Resin with Epoxy- and Methacrylate-Functionalized Silica Sols to Improve the Ablation Resistance of Their Glass Fiber-Reinforced Composites

“…The functionalized silica sols (GPSD, MPS and GPS-MPS) were prepared following procedures described in the literature [12,13]. Briefly, formic acid (50 mol % relative to total Si) and water (100 mol % relative to total Si) produced the hydrolytic condensation of TEOS (15 wt %) with GPMS (15 wt %), in the presence of DGEBA, to afford GPSD, or with MPMS (15 wt %) to afford MPS, or with GPMS (7.5 wt %) and MPMS (7.5 wt %) to afford GPS-MPS.…”

“…Briefly, formic acid (50 mol % relative to total Si) and water (100 mol % relative to total Si) produced the hydrolytic condensation of TEOS (15 wt %) with GPMS (15 wt %), in the presence of DGEBA, to afford GPSD, or with MPMS (15 wt %) to afford MPS, or with GPMS (7.5 wt %) and MPMS (7.5 wt %) to afford GPS-MPS. The addition of DGEBA to GPMS reduces the hydrolysis or alcoholysis of epoxy rings during the hydrolytic condensation [12]. The hydrolytic condensation led to soluble products, despite the use of significant amounts of TEOS [22], due to the network blocking characteristics of the GPMS and MPMS monomers (they are trifunctional monomers while TEOS is a tetrafunctional monomer), and the low water to silicon ratio (1:1) used [23].…”

“…The hydrolytic condensation led to soluble products, despite the use of significant amounts of TEOS [22], due to the network blocking characteristics of the GPMS and MPMS monomers (they are trifunctional monomers while TEOS is a tetrafunctional monomer), and the low water to silicon ratio (1:1) used [23]. The large fraction of intramolecular cycles produced in these polymerizations also favours the generation of soluble products [12,[16][17][18].…”

“…However, many other types of modifiers such as silica precursors can also be used for this purpose. It has been reported that modification of thermosetting polymers with polyhedral oligomeric silsesquioxanes (POSS), or silsesquioxanes and functionalized silica sols, increases the mechanical and thermal properties of the cross-linked polymer and the residual mass after degradation at high temperatures [10][11][12][13][14][15]. Silsesquioxanes (or polysilsesquioxanes) are the condensation products of organotrialkoxysilanes [10,[16][17][18], while functionalized silica sols are obtained by the co-condensation of organotrialkoxysilanes with a silica precursor such as tetraethoxysilane (TEOS) [12,13].…”

Modification of graphene with silica nanoparticles for use in hybrid network formation from epoxy, novolac, and epoxidized novolac resins by sol-gel method: Investigation of thermal properties

“…These organic-inorganic hybrid materials can be prepared by co-condensation of modified polymers with metal alkoxides and formation of covalent bonding between the organic and inorganic components [16]. In sol-gel methods, hydrolysable alkoxysilanes are commonly used as coupling agents and pH, alkoxide type, water amount, temperature, and drying methods are important factors controlling the hydrolysis and condensation reactions [17][18][19][20]. Uniform distribution of silica/siloxane domains within a polymer matrix in co-condensation process may result in higher thermal and mechanical properties in such hybrid materials.…”