Study the Rheological and Mechanical Properties of PVA

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  Chemistry and Materials ISSN 2224-   3224 (Print) ISSN 2225-   0956 (Online)Vol 1, No.1, 2011 20 | Page  Study the Rheological and Mechanical Properties of PVA/NH 4 Cl by Ultrasonic 1 Prof. Dr. Abdul-Kareem Jawad Rashid 2 Rawaa Mizher Obiad 3 Burak Yahya Kadem1. University of Babylon, College of Science, Physics Department, Babylon, Hilla -Najif Street, Iraq2. University of Babylon, College of Science, Physics Department, Babylon, Hilla -Najif Street, Iraq3. University of Babylon, College of Science, Physics Department, Babylon, Hilla -Najif Street, Iraq* E-mail of the corresponding author: 1 3   Abstract Some of physical properties of polyvinyl alcohol dissolves in distilled water had been studied atdifferent concentration (0.25%, 0.5%, 0.75%, 1.0%, and 1.25%) before and after adding 1gm fromNH 4 Cl for all concentrations, the Rheological properties such as shear viscosity, relative viscosity andreduced viscosity are measured and after that the ultrasonic velocity had been measured by ultrasonicwaves system at frequency 40 KHz, other mechanical properties had been calculated such as absorptioncoefficient of ultrasonic waves, relaxation time, relaxation amplitude, specific acoustic impedance,compressibility and bulk modules. Another acoustic mechanical properties were measured andcalculated at a same time such as the ultrasonic wave amplitude before and after absorption by solutionwere showed on oscilloscope ,then we calculated absorption coefficient. The results show that all theseproperties are increasing with the increase of the polymer concentration except velocity is decreasingwith increase the concentration; results also show that when adding NH 4 Cl these properties areincreasing.  Keywords: PVA solution, mechanical properties, rheological properties, ultrasound technique. 1. Introduction PVA is a water-soluble synthetic polymer, due to the characteristics of easy preparation, goodbiodegradability, excellent chemical resistance, and good mechanical properties, polyvinyl alcohol isused mainly as a solution in water but its solubility in water depends on its degree of polymerizationand degree of hydrolysis of its precursor (poly vinyl acetate). Solvent effects might therefore beexpected to influence the ultrasonic relation behavior, the absorption of ultrasonic in liquid polymersystems is governed by local modes of motion (segmental conformation change) and cooperative wholemolecule movement (normal or Rouse modes), because of the existence of strong intermolecularinteraction within the polymer it should be possible to observe cooperative motion in the ultrasonicrange (Jayanta et. al. 2004). Acoustic relaxation measurements on other polymers have been reportedby several workers (Tomasz et. al. 2010, Hassun et. al. 1990 & Khalida 2004). Ultrasonic technique isgood method for studying the structural changes associated with the information of mixture assist in thestudy of molecular interaction between two species; some of mechanical properties of differentpolymers were carried by some workers using ultrasonic technique. (Al-Bermany E.2004 & B. Boro2009). 2. Experimental:   2.1 Preparation of Solutions: The solution was prepared by soluble PVA with different weights (1, 2, 3, 4 and 5) gm in (400 ml)distilled water under stirring and 70 o C for (1 hour) the resulting solution was stirred continuously untilthe solution mixture became a homogeneous, the PVA concentrations were (0.25%, 0.5%, 0.75%, 1.0%and 1.25%); after that (1gm) of NH 4 Cl is adding to all concentrations to study the addition affect. 2.2 Density and Rheological measurements: The density of the solution ( ρ ) was determined by density bottle method and their viscosities measuredbefore and after adding 1gm from NH 4 Cl for all concentrations using Ostwald viscometer withaccuracy of ± 1.05%, the method of measurement has been described by (Al-Bermany E.2004),elsewhere different types of shear viscosity were determined before and after the adding of NH 4 Cl bythe following equations (Abdul-Kareem J. Rashid and Burak 2011).The Shear viscosity had been  Chemistry and Materials ISSN 2224-   3224 (Print) ISSN 2225-   0956 (Online)Vol 1, No.1, 2011 21 | Page  calculated by the following equation ( Subhi et. al. 1990) : )1(.......... s oot t o ρ  ρ η η  =  Where ( ρ ) and ( η s ) are the solution density and viscosity respectively, ( ρ o ) and ( η o ) are density andviscosity of distilled water respectively, Relative viscosity ( η rel ) was calculated by the followingequation. )2(.......... osot t rel η η η  ==  The specific viscosity ( η sp ) and reduced viscosity ( η red ) was calculated by the equations where (C) is theconcentration: )3.....(..........1 )( s −=−= reloos p η η η η η    )4(.......... r C sped  η η  =   2.3 Ultrasonic measurements: Ultrasonic measurements were made by pulse technique of sender-receiver type (SV-DH-7A/SVX-7velocity of sound instrument) with different frequencies (25, 30,35,40,45 and 50 kHz) in our study thefrequency fixed at (40 KHz), the receiver quartz crystal mounted on a digital vernier scale of slowmotion, the receiver crystal could be displaced parallel to the sender and the samples were put betweensender and receiver. The sender and receiver pulses (waves) were displaced as two traces of cathoderay oscilloscope, and the digital delay time (t) of receiver pulses were recorded with respect to thethickness of the samples (x). The pulses height on oscilloscope (CH1) represents incident ultrasonicwave’s amplitude (A 0 ) and the pulses height on oscilloscope (CH2) represents the receiver ultrasonicwave’s amplitude (A). 2.4 Theoretical calculation: The absorption coefficient ( α ) was calculated from Lambert – Beer law (Zong fang et. al. 2011):A/A 0 = e (- α x) …… (5)Where (A 0 )is the initially amplitude of the ultrasonic waves,(A) is the wave amplitude after absorptionand (x) is the thickness of the sample, the transmittance (T) is the fraction of incident wave at aspecified wavelength that passes through a sample was calculated from the following equation (Dipak 2001):T = I / Io ……… (6)Where (I 0 ) is the initially intensity of the ultrasonic waves and (I) is the received intensity. Theultrasonic wave velocity (v) was calculated using the following equation (Abdul-Kareem et. al. 2011):v = x / t …… (7)Where (t) is time that the waves need to cross the samples (digital obtained from the instrument).Attenuation is generally proportional to the square of sound frequency so the relaxation amplitude (D)was calculated from the following equation (Josef and Herbert 1990) where (f) is the ultrasonicfrequency:D = α  / f  2 ……… (8)The acoustic impedance of a medium (Z), it was calculated by equation (Jarth 2008):Z = ρ v …….. (9)Bulk modulus (B) is the substance's resistance to uniform compression, it is defined as the pressureincrease needed to decrease the volume; it was calculated by Laplace equation (Al-Bermany E.2004):B = ρ v 2 ……. (10)Compressibility ( β ) is a measure of the relative volume change of a fluid or solid as a response to apressure (or mean stress) change, it was calculated by the following equation (Hassina et. al. 2009): β = ( ρ v 2 ) -1 …….. (11)The relaxation time ( τ ) was calculated from the equation (Herbert 1985): τ =4 η s /3 ρ v 2 …….. (12)   3. Results and Discussion:  Chemistry and Materials ISSN 2224-   3224 (Print) ISSN 2225-   0956 (Online)Vol 1, No.1, 2011 22 | Page  3.1 Rheological properties: The density is increasing with the increase of polymer concentration as shown in (Fig.1) since thedensity defined as mass per unit volume and we adding different weight of polymer to fixed volume of solvent so there are linear increment for density. Shear Viscosity is increasing with concentration asshown in (Fig.2) this attributed to the mechanism that hydrogen bonding of water attached to oxygensites, this leads to salvation sheaths and increase in the size of the molecules, so its viscosity (Subhi 1990) furthermore water act as plasticizer will reduce tensile strength and increase its chains (Al-Bermany 2010). Relative, specific and reduced viscosities showed in (Fig.3), (Fig.4) and (Fig.5)respectively posses the same behaviors of shear viscosity because they derived from it as shown inequations (2, 3), adding NH 4 Cl made   enhancement for these viscosities, this attributed that there areintermolecular interactions and network formation between the two types of molecules as a result of adding NH 4 Cl so increasing the size of macromolecules that increasing shear viscosity (Kumagai et. al.  1978). 3.2 Mechanical properties: (Fig.6) shows that absorption coefficient is increasing with concentration this attributed to the fact thatwhen polymer concentration increase there will be more molecules in solution this lead to moreattenuation against wave propagation, the attenuation can be attributed to the friction and heatexchange between the particles and the surrounding medium as well as to the decay of the acousticwave in the forward direction due to scattering by the Particles (Tomasz et. al. 2010), this behaviorsame to that give by (Al-Bermany E. 2004) & Hassun and Rahman 1990) for other polymers, addingNH 4 Cl enhances absorption coefficient by increasing its values. The transmittance is decreasing withincreasing concentration as shown in (Fig.7) this attributed that the polymer molecules absorbed thesound waves according to Lambert-Beer Law which is biased on concentration (Ingle and Stanley1988). Ultrasonic velocity is decreasing with increasing concentration as shown in (Fig.8) this becausestructural or volume relaxation it occurs in associated liquids such as polymers, a liquid when at resthas a lattice structure similar to that possessed by solid when waves are propagated through it, theresultant periodic changes of wave pressure causes molecules to flow into vacancies in the latticeduring compression phase and to return to their srcinal positions in the lattice during rarefaction sowhen concentration increases the velocity will be decrease, because there are more attenuation of polymer molecules to ultrasound waves (Al-Bermany K.J. 2010). Adding NH 4 Cl reduces the velocitybecause of increasing network formation between polymer chains against the ultrasonic velocity waves.Ultrasonic relaxation time was calculated by using equation no. (12) Shown in (Fig.9) and therelaxation amplitude shown in (Fig.10) calculated from equation no.(8) their values are increasing withconcentration, this behavior same to that give by (Hassun and Rahman 1990) & Al-Bermany 2009) forother polymers and attributed to the fact that ultrasonic energy depends on viscosity thermalconductivity, scattering and intermolecular processes , thermal conductivity and scattering effects areknown to be negligible (Abdul-Kareem et. al. 2011 & Josef and Herbert 1990) so viscosity isresponsible for the increase of relaxation amplitude for this reason absorption coefficient commonlyknown as visco –absorption. Specific acoustic impedance shown in (Fig.11) is decreasing withconcentrations this behavior same to that given by (Al-Bermany 2009) & Subhi et. al. 1990) for otherpolymers and attributed to the equation no. (9) has only one variable parameter which is velocity anddensity has very small variations with respect to that of velocity. The compressibility is increasing withthe increase of concentration (Fig.12) and attributed to the fact that in Laplace equation no. (10) Thereare inverse proportionality between compressibility and ultrasonic velocity and the bulk modulus isdecreasing with concentration (Fig.13). 4. Conclusion Adding NH 4 Cl made enhancement for the viscosity, the viscosity is responsible for the increase of relaxation amplitude, this study shows that intermolecular processes are responsible for the relaxation,and indicating increase in the size of molecules in bath of ultrasonic waves then reducing the velocity.When concentration increases the velocity decreases there will be complexes molecules were formed inthe solution by the effect of peroxide and roots that rebounded to formations between polymer chainswhen adding NH 4 Cl.The polymer molecules absorbed the sound waves according to Lambert-BeerLaw which is biased on concentration so reducing velocity and transmittance. References  Chemistry and Materials ISSN 2224-   3224 (Print) ISSN 2225-   0956 (Online)Vol 1, No.1, 2011 23 | Page  Abdul-Kareem J. Rashid and Burak Y. Kadem (2011) “Effect of variable ultrasonic frequencies onsome physical properties of Iraqi palm fiber PVA composite”  Journal of Asian Scientific Research ,1( 7 ).359-365Abdul-Kareem J. Rashid, Ehssan Dhiaa Jawad and Burak Y. Kadem (2011) “A Study of SomeMechanical Properties of Iraqi Palm Fiber-PVA Composite by Ultrasonic”    European Journal of Scientific Research,   61 (2). 203-209.Al-Bermany K.J. (2009) “Enhancement mechanical and rheological properties and some its differentindustrial applications “  journal of college of education, 4(  3 ).380- 384.Al-Bermany E.(2004) “Gamma radiation effect in some physical properties of polymer zanthancellulose”  M.Sc. thesis , Baghdad university, Iraq.Al-Bermany K.J.(2010) “Enhancement of mechanical properties using gamma radiation for HECpolymer” ,  Journal of college of Education ,Babylon university,1( 5 ).10-15.B. 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