| 1. |
- Ebrahimzadeh, PR, et al.
(författare)
-
A model of the dynamic mechanical responses of wood, paper and some polymers to moisture changes
- 1998
-
Ingår i: Journal of Materials Science. - SPUIBOULEVARD 50, PO BOX 17, 3300 AA DORDRECHT, NETHERLANDS : KLUWER ACADEMIC PUBL. - 0022-2461 .- 1573-4803. ; 33:5, s. 1201-1209
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamic mechanical responses of Scots pine, paper, PA6, cellophane, PVAc and PUR samples subjected to changes in the relative humidity of the surrounding air from 5 to 85% and vice versa have been analysed semiquantitatively on the basis of coupled non-linear rate equations for the moisture concentration in the sample as a function of the time. Important characteristics of the diffusion of moisture into and out of the samples have been studied by measuring the sample weight as a function of time. Moisture sorption results in sample swelling in Scots pine, paper, PA6, cellophane and PUR, for all of which mechanical loss peaks were detected. For PVAc, which does not bind moisture at load-bearing hydrogen bonding sites, no mechanical loss peak could be found. Characteristic of the mechanical loss at low vibration frequencies (0.01 to 1 Hz) is a peak immediately following a change in relative humidity for all studied sample materials except PVAc. This peak is almost certainly due to modulation of the number of load-bearing hydrogen bonds in the material. The relation between the width of the mechanical loss peak and the duration of the moisture sorption and desorption processes is interpreted according to an accepted model of two water molecule binding modes, one in which load-bearing hydrogen bonds are broken unimolecularly by water molecules and one in which further water molecules form clusters on the already unimolecularly bound water. (C) 1998 Chapman & Hall.
|
|
| 2. |
- Ebrahimzadeh, PR, et al.
(författare)
-
Dynamic mechanical characterization of mechanosorptive effects in wood and paper
- 1996
-
Ingår i: European Journal of Wood and Wood Products. - 0018-3768 .- 1436-736X. ; 54:4, s. 263-271
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamic mechanical studies in dual cantilever and tensile stretching mode of Scots pine veneer, birch veneer and paper under stepwise humidity changes between 5% and 85% relative humidity are reported. The loss tangent (tan delta) shows a transient peak every time the relative humidity of the surrounding atmosphere is changed. In the bending mode a clamping arrangement that is freely movable in the longitudinal direction gives more distinct damping peaks than does a static fixture.There is a close relationship between the rate of sorption/desorption and the shape of the tan delta peak. In response to reduction of the rate of humidity change the damping transients slowly disappear. They also diminish in strength as the temperature is raised toward 60 degrees C. Their strengths increase as the measuring frequency is lowered toward 0.01 Hz. Also, when the samples are highly compressed or prestressed with static loads the peak heights are greatly reduced. The tans peaks become less distinct and eventually disappear when the amplitude of the vibration increases. Long time testing results in significant changes in the shapes of the tan delta versus time data.A working hypothesis is that these phenomena are closely related to molecular diffusion of water through the sample material. Simple estimates show that the relaxation time for a diffusion related process should be of the order of a minute.
|
|
| 3. |
- Rychwalski, Rodney, 1945, et al.
(författare)
-
CF, CB and SWNT Polymer Composites
- 2003
-
Ingår i: The National Conferences on Polymer Characterization, X Seminar TWORZYWA SZTUCZNE W BUDOWIE MASZYN (Plastics in Machine Design), Cracow University of Technology, Cracow (Poland), September 29-October 1, 2003. ; , s. 347-357
-
Konferensbidrag (refereegranskat)
|
|
| 4. |
- Rychwalski, Rodney, 1945, et al.
(författare)
-
New polymeric micro-and nanocomposites
- 2003
-
Ingår i: Proceedings of the Polish-Swedish Symposium: Materials-Energy Supply-Environment & Society, Chalmers University of Technology, Göteborg (Sweden), December 12, 2003. ; , s. 25 - 32
-
Konferensbidrag (refereegranskat)
|
|
