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Kinetic study of photodegradation of water soluble polymers

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Abstract

The kinetic models of the photo-oxidative degradation of water-soluble polymers, as the main component of water-soluble composite films in aqueous solutions, by ultraviolet radiation and hydrogen peroxide (UV/H2O2) are developed. The rate expressions of the photochemical degradation of soluble polymers are developed based on the mass balance of the main chemical species in water. Continuous-distribution kinetics is applied for the kinetic modeling of the photo-oxidative degradation of polymers in aqueous solutions based on the population balance equations (PBEs). It is assumed that the random chain scission is the mechanism of the chain cleavage. The PBEs are solved by the moment operation which transforms the integro-differential equations into ordinary differential equations that could be readily solved to obtain the rate coefficients of the polymer photodegradation. The model predictions for the number average molecular weight and the number of chain scissions per molecules are in good agreement with the experimental data obtained from the open literature for the photodegradation of poly(ethylene glycol) by the UV/H2O2 process in aqueous solution. The results confirmed the random chain scission assumption. The sequential quadratic programming was used as an optimization technique to find the kinetic parameters that could be used for scaling-up purposes.

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Abbreviations

b :

UV path length (cm)

C :

Concentration (M)

\( e_{\lambda }^{\text{a}} \) :

Local volumetric rate of energy absorption (Einstein L−1 s−1)

F(k):

Objective function

I o :

UV light intensity (Einstein L−1 s−1)

k i :

Rate constant (M−1 s−1), (s−1)

K a :

Equilibrium constant

m :

Parameter indicating the shape of scission fragment distribution

M n :

Number average molecular weight (g mol−1)

p (n) :

The nth moment of p(x,t)

p(x):

Polymer chain of molecular weight x

p(x,t):

Molecular weight distribution of the polymer of molecular weight x

r(x,t):

Molecular weight distribution of the radical of molecular weight x

R\( ^{\cdot}\)(x):

Polymer radical of molecular weight x

S :

Number of chain scission per molecule

T :

Time (s)

x :

Molecular weight (g mol−1)

y i :

Simulated data points

y i,m :

Experimental data points

AOT:

Advanced oxidation technology

LCA:

Long chain scission

MW:

Molecular weight

MWD:

Molecular weight distribution

PBE:

Population balance equation

PEG:

Poly(ethylene glycol)

SQP:

Sequential quadratic programming

TIC:

Theil’s inequality coefficient

UV:

Ultraviolet

\( \Upgamma \) :

Gamma function

\( \varphi \) :

Quantum yield (mol Einstein−1)

\( \Upomega (x,x^{\prime}) \) :

Stoichiometric kernel function for fragmentation process

\( \varepsilon \) :

Molar extinction coefficient (M−1 cm−1)

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Acknowledgments

The financial support of Natural Sciences and Engineering Research Council of Canada (NSERC) and Ryerson University is greatly appreciated.

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Authors and Affiliations

  1. Department of Chemical Engineering, Ryerson University, Toronto, ON, M5B 2K3, Canada

    S. Ghafoori, M. Mehrvar & P. K. Chan

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  1. S. Ghafoori
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  2. M. Mehrvar
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  3. P. K. Chan
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Correspondence to M. Mehrvar.

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Ghafoori, S., Mehrvar, M. & Chan, P.K. Kinetic study of photodegradation of water soluble polymers. Iran Polym J 21, 869–876 (2012). https://doi.org/10.1007/s13726-012-0091-5

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