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| | 51 years old Film, Television, Radio and Stage Owners Dominic from High River, has many interests that include model rockets, property developers [http://www.luv2love.com/activity/p/256108/ ec in singapore] singapore and rowing. Finds travel a terrific experience after touring The Causses and the Cévennes. |
| '''Rheological weldability''' (''RW'') is proposed as a criterion to determine reliably [[weldability]] of [[thermoplastics]]. In a practical manner, ''RW'' of [[thermoplastics]] is assessed through their rheological properties: [[viscosity]] (''η'') and [[activation energy]] (''E''<sub>a</sub>). According to ''RW criterion'', the lower the [[viscosity]] (''η'') and the lower the absolute value of [[activation energy]] (|''E''<sub>a</sub>|), the better the [[weldability]].<ref name="PES2008">{{cite journal | ISSN=1548-2634 | url=http://onlinelibrary.wiley.com/doi/10.1002/pen.21014/abstract | title=Effects of welding procedures on mechanical and morphological properties of hot gas butt welded PE, PP, and PVC sheets | author=O.Balkan, H.Demirer, A.Ezdesir, H.Yildirim | journal=Polymer Engineering Science | year=2008 | volume=48 | page=732}}</ref><ref name="IMSP2008">{{cite book|author=O.Balkan, A.Ezdesir|title=Rheological Weldability of Polymers|publisher=12. International Materials Symposium (12.IMSP) Denizli|date=October 15-17, 2008|page=1046}}</ref>
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| ==[[Viscosity]]==
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| ===The lower the ''η'', the better the ''RW''===
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| Regarding [[sessile drop technique]], [[wetting]] is characterized by degree of interfacial contact and quantified via [[contact angle]] (''θ''<sub>c</sub>) of a liquid on a solid surface at [[equilibrium]], as shown in Fig. 1. Interrelation between [[contact angle]] and [[surface tension]]s at [[equilibrium]] is given by the Young equation:<ref>{{cite journal|first = T.|last = Young|title = An Essay on the Cohesion of Fluids|journal = [[Philosophical Transactions of the Royal Society|Phil. Trans. R. Soc. Lond.]]|volume = 95|pages = 65–87|year = 1805|doi = 10.1098/rstl.1805.0005}}</ref>
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| :<math>\gamma_{SG}\ =\gamma_{SL}+\gamma_{LG}\cos{\theta_{c}},</math>
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| where
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| * <math>\gamma_{SG}</math> = Solid-Gas surface tension,
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| * <math>\gamma_{SL}</math> = Solid-Liquid surface tension,
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| * <math>\gamma_{LG}</math> = Liquid-Gas surface tension,
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| * <math>\theta_{c}</math> = Contact angle.
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| [[image:Contact angle.svg|thumb|400px|right|Fig 1: An illustration of the sessile drop technique with a liquid droplet partially wetting a solid substrate at [[equilibrium]]. <math>\theta_C</math> is the contact angle, and <math>\gamma_{SG}\ </math>, <math>\gamma_{LG}\ </math>, <math>\gamma_{SL}\ </math> represent surface tensions of the solid–gas, gas–liquid, and liquid–solid interfaces, respectively.]]
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| For perfectly good [[wetting]], [[contact angle]] (''θ''<sub>c</sub>) at [[equilibrium]] should be a minimum. However, it is valid only at [[equilibrium]], and rate of the [[equilibrium]] depends on the balance between driving force of [[wetting]] and [[viscosity]] of the liquid. In the case of [[polymer]] melts, [[viscosity]] can be very high and it may take a long time to reach the equilibrium contact angle (dynamic contact angle is likely higher than the contact angle at equilibrium).
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| Consequently, for the evaluation of [[weldability]], [[viscosity]] of molten [[thermoplastics]] ([[polymer]] melts) have to be taken into account since [[welding]] is a rapid process. It can be said that the lower the [[viscosity]], the better the [[weldability]].
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| Recalling that [[viscosity]] (''η'') decreases with increasing temperature (''T'') and [[shear rate]] (<math>\dot\gamma</math>) for most [[polymer]] melts, [[weldability]] is better where temperature and [[shear rate]] (movement) are higher within all cross-section of welding region.<ref name="PES2008"/><ref name="IMSP2008"/>
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| ==[[Activation energy]]==
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| ===The lower the |''E''<sub>a</sub>|, the better the ''RW''===
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| During operation of a welding process, soften or molten portion of [[thermoplastics]] ([[polymer]] articles) is able to flow through the interface. Smaller amount of flow causes smaller diffusion at the interface and lower weld strength. In order for a [[polymer]] melt to flow, macromolecular chain segments must be able to move. When the chain segments obtain sufficient thermal energy to overcome energy barrier, they can move readily. The energy barrier is called as [[activation energy]] (''E''<sub>a</sub>). It can be said that if a [[polymer]]’s absolute value of [[activation energy]] (|''E''<sub>a</sub>|) is lower, its [[weldability]] becomes better.
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| |''E''<sub>a</sub>| values of such polymers as [[PVC]] decrease with increasing [[shear rate]] (<math>\dot\gamma</math>), implying better [[weldability]] where [[shear rate]] (movement) are higher within all cross-section of welding region.<ref name="PES2008"/><ref name="IMSP2008"/>
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| Using [[viscosity]]-[[shear rate]] (<math>\eta - \dot\gamma</math>) data at various temperatures for a [[polymer]], [[activation energy]] (''E''<sub>a</sub>) can be calculated via [[Arrhenius equation]]:
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| :<math>\eta = C \exp \left( \frac{-E_a}{RT} \right),</math>
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| where
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| * ''η'' is [[viscosity]] of molten polymer,
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| * ''C'' is [[pre-exponential factor]],
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| * ''R'' is [[universal gas constant]],
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| * ''T'' is temperature ([[Kelvin]]).
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| How to calculate absolute value of [[activation energy]] (|''E''<sub>a</sub>|) by taking the [[natural logarithm]] of [[Arrhenius equation]] can be readily learned elsewhere (see [[Arrhenius equation]]).
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| == See also ==
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| * [[Activation energy]]
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| * [[Arrhenius equation]]
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| * [[Plastic welding]]
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| * [[Rheology]]
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| * [[Weldability]]
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| * [[Welding]]
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| * [[Wetting]]
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| ==References==
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| {{Reflist}}
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| [[Category:Welding]]
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| [[Category:Rheology]]
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51 years old Film, Television, Radio and Stage Owners Dominic from High River, has many interests that include model rockets, property developers ec in singapore singapore and rowing. Finds travel a terrific experience after touring The Causses and the Cévennes.