Hot press bonding

The possibility of using graft polymerization of styrene on to allylated wood to provide covalent bonding between surfaces was also investigated (Ohkoshi, 1991). In this case, a free-radical initiator (BPO) was present in the styrene monomer that was used to impregnate the allylated wood, prior to hot-pressing. Bond strength was determined by... 

Use Hot-press bonding of furniture veneers, premium wall paneling. 

Fusion bonding Hot press bonding Thermal bonding... 

The first industrial hardboard was developed by W. Mason in the mid-1920s he found that a mat of wet fiber pressed in a hot press would produce a self-bonded flat panel with good strength, durabiUty, and stabiUty. The product was patented in 1928, trademarked as Masonite, and commercial production began. Over time several other processes for producing hardboards have been developed from modifications of the original process. Brief descriptions of these processes foUow and a flow chart of the process is shown in Figure 5. 

Reaction-bond ed Sintered Sintered beta alpha Hot-pressed (AI2O3)" Sintered... 

Fig. 3. Stress mpture behavior in air at 1200°C for SiC stmctural ceramics —hot-pressed -, reaction-bonded , sintered alpha —sintered beta. To...

Fig. 4. Thermal diffusivity of silicon-based stmctural ceramics (a) reaction-bonded SiC (b) hot-pressed and sintered SiC (c) hot-pressed (1% MgO,...

Property Reaction-bonded Sintered Hot-pressed isostaticaHy Hot-pressed ... 

Silicon Nitride. SiUcon nitride is manufactured either as a powder as a precursor for the production of hot-pressed parts or as self-bonded, reaction-sintered, siUcon nitride parts. a-SiUcon nitride, used in the manufacture of Si N intended for hot pressing, can be obtained by nitriding Si powder in an atmosphere of H2, N2, and NH. Reaction conditions, eg, temperature, time, and atmosphere, have to be controlled closely. Special additions, such as Fe202 to the precursor material, act as catalysts for the formation of predorninately a-Si N. SiUcon nitride is ball-milled to a very fine powder and is purified by acid leaching. SiUcon nitride can be hot pressed to full density by adding 1—5% MgO. 

In general, the purified boron carbide is ultimately obtained as a granular soHd that subsequendy may be molded or bonded into usehil shapes. To achieve high density and strength, it is hot pressed at 1800—2400°C in graphite molds. 

There are two further processes. Silicon-based ceramics can be fabricated by sintering or by hot-pressing. But a new route, reaetion bonding (Fig. 19.6), is cheaper and gives good precision. If pure silicon powder is heated in nitrogen gas, or a mixture of silicon and carbon powders is sintered together, then the reactions... 

Even though UF adducts are known to be present in OSB, formaldehyde emissions are not elevated over those expected of an unmodified PF. There are three reasons for this. First, the molar ratio of formaldehyde-to-urea in these situations is very low. It is at least an order of magnitude lower than practical molar ratios for curable UF resin binders. Second, UF adducts are quite stable under the alkaline conditions that prevail in PF-bonded OSB. Finally, the urea only reacts with the formaldehyde that was left behind during polymerization and would have been largely emitted in pressing and cool-down. Urea additions have been shown to reduce PF formaldehyde emissions from hot pressing [121 ]. 

The urea usually is added to the finished PF-resin and causes a distinct decrease of the viscosity due to disruption of hydrogen bonds [95] and due to dilution effects. There is obviously no co-condensation of this post-added urea with the phenolic resin. Urea only reacts with the free formaldehyde of the resin forming methylols, which, however, do not react further due to the high pH [19]. Only at the higher temperatures of the hot-press does some phenol-urea co-condensation occur [93,94,96]. 

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