The Hot Pressing of Dry-formed Wood-based Composites. Part IV. Predicted Variation of Mattress Moisture Content with Time

Bolton, A. J.; Humphrey, Philip E.; Kavvouras, P. K.

doi:10.1515/hfsg.1989.43.5.345

Cited by 24 publications

(13 citation statements)

References 4 publications

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“…12,14 The solid phase 13 C NMR spectrum of the hardened reaction products of a non blocked polymeric MDI (pMDI) with water shown in Figure 1 correspond to the shifts in Table I. Thus, the peak at 137.2 ppm belongs to the aromatic carbon (Fig.…”

Section: Resultsmentioning

confidence: 92%

¹³C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates

Despres¹,

Pizzi²,

Delmotte

2005

J of Applied Polymer Sci

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A solid state 13 C NMR study of hardened networks obtained by the reaction of blocked and nonblocked isocyanates (pMDI) with urea-formaldehyde (UF) resins in water showed different results according to the temperature of the reaction. At high temperature, in water, both a nonblocked or an emulsifiable, blocked isocyanate, appear to crosslink with UF resins through the formation both of traditional methylene bridges connecting urea to urea and of urethane bridges. The latter have been confirmed by 13 C NMR to form in water by reaction of the isocyanate -NACAO group with the hydroxymethyl groups of the UF resin. At ambient temperature, UF/pMDI resins where the pMDI is a emulsifiable blocked isocyanate, do not appear to form urethanes to any great extent but rather to crosslink through the usual UF resin urea to urea methylene bridges. Even in this case, when urethane bridges appear to be absent, evidence of crosslinking in water through reaction of the isocyanate with the -NH 2 and -NHamide of the UF resin has not been observed.

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Section: Resultsmentioning

confidence: 92%

¹³C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates

Despres¹,

Pizzi²,

Delmotte

2005

J of Applied Polymer Sci

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“…Heat transfer from the surface to the core is mainly convective through the movement of steam. As a result, the moisture near the face decreases at the onset of pressing, while that at the core rises (Bolton et al 1989). The temperature rises within the core and the internal pressure increases with increasing mat MC or platen temperature (Kamke and Casey 1988;Song and Ellis 1997).…”

Section: Pressing Studiesmentioning

confidence: 99%

Flake Drying Temperature Affects Mat Properties during Pressing

Martino¹,

Shrauti²,

Banerjee³

et al. 2002

Holzforschung

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IntroductionNumerous studies have established that the surface of wood is inactivated when overdried. Christiansen (1990Christiansen ( , 1991 studied the effect of overdrying on the glue bond. The movement of extractives to the surface, reorientation of molecules on the wood surface and irreversible closure of large micropores in cell walls were identified as contributing factors. For Southern pine, the movement of extractives during drying was believed to lead to poor wettability. Hemingway (1969) demonstrated the reduction in surface wettability of yellow birchwood after heating, and Yazaki et al. (1994) showed that the uneven extractives distribution in blackbutt veneers made high quality bonding difficult to achieve with phenolic adhesives. Jordan and Wellons (1977) showed that commercial drying of veneer damaged the surface, and that extractive content and type had a major effect on wettability. These studies provide ample evidence that drying temperature inactivates the wood surface. In this paper we demonstrate that surface properties also influence the pressure developed in the core during pressing. Materials and MethodsGreen veneer (Pinus taeda) was obtained from the GeorgiaPacific mill in Madison, GA, and was used as received. Sapwood was the predominant fraction present. Specimens (25.4 × 25.4 × 3.2 mm) were first dried to moisture contents (MC) of less than 25% in a 105°C oven. Contact angles were measured on the tight side of the veneer after allowing the specimen to cool. The specimen was then returned to the oven, dried to a lower MC, and the procedure was repeated.Pine flakes were obtained from the Georgia-Pacific facility at Dudley, NC, and were moisture-equilibrated in plastic bags before use. The mill uses a high-temperature rotary dryer, to dry the furnish to 5% MC. Two presses were used. Small-scale work was done in an electrohydraulic press (Banerjee et al. 1998a) with platens of 14 cm diameter. The temperature of a stack of flakes (without added resin) was measured during pressing. The stack was placed inside a stainless steel bag fitted with inlet and outlet tubes. The top of the bag contacted a 200°C platen and the bottom was insulated with a dry felt. The temperature at the bottom would correspond to that at the center of a mat if both platens of the press were heated. The press closed in about 1 s at an applied pressure of 18 atm. The thermocouple was positioned in the mat at a distance of 2.2 mm (after pressing) from the top platen.Larger-scale pressing was done at the Georgia-Pacific laboratory in Decatur, GA, where 1.14 kg (dry basis) of wood was pressed at the temperature and pressure listed above to create 929 cm 2 × 1.9 cm boards.Contact angles were measured with a First Ten Angstroms FTA 200 instrument, and were averaged from five determinations. A piece of veneer was placed under a syringe that delivered a 500 µl water drop. A computer-controlled camera captured images of the drop at predetermined time intervals; image analysis software was then used to determine the contact ang...

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“…Heat transfer from the surface to the core is mainly convective through the movement of steam. As a result, the moisture near the face decreases at the onset of pressing, while that at the core rises (Bolton et al, 1989). The temperature rise within the core and the internal pressure increases with increasing mat MC or platen temperature (Kamke and Casey 1988;Song and Ellis 1997).…”

Section: Resultsmentioning

confidence: 99%

Implementing Strategies for Drying and Pressing Wood Without Emissions Controls

Banerjee¹,

Conners²

2007

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Drying and pressing wood for the manufacture of lumber, particleboard, oriented strand board (OSB), veneer and medium density fiberboard (MDF) release volatile organic compounds (VOCs) into the atmosphere. These emissions require control equipment that are capitalintensive and consume significant quantities of natural gas and electricity. The objective of our work was to understand the mechanisms through which volatile organic compounds are generated and released and to develop simple control strategies.

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The Hot Pressing of Dry-formed Wood-based Composites. Part IV. Predicted Variation of Mattress Moisture Content with Time

Cited by 24 publications

References 4 publications

¹³C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates

¹³C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates

Flake Drying Temperature Affects Mat Properties during Pressing

Implementing Strategies for Drying and Pressing Wood Without Emissions Controls

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The Hot Pressing of Dry-formed Wood-based Composites. Part IV. Predicted Variation of Mattress Moisture Content with Time

Cited by 24 publications

References 4 publications

13C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates

13C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates

Flake Drying Temperature Affects Mat Properties during Pressing

Implementing Strategies for Drying and Pressing Wood Without Emissions Controls

Contact Info

Product

Resources

About

¹³C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates

¹³C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates