On the electron beam-induced degradation of vinyl ester thermosets

Lorelis González-López; Logan T. Kearney; Chris Janke; James F. Wishart; Amit K. Naskar; Nihal Kanbargi; Fred B. Bateman; Mohamad Al-Sheikhly

doi:10.1016/j.polymdegradstab.2023.110307

On the electron beam-induced degradation of vinyl ester thermosets

Lorelis González-López, Logan T. Kearney, Chris Janke, James F. Wishart, Amit K. Naskar, Nihal Kanbargi, Fred B. Bateman, Mohamad Al-Sheikhly

Carbon and Composites

Research output: Contribution to journal › Article › peer-review

Abstract

We have demonstrated that electron beam radiolysis induces scissions of the C-O-C bonds along the backbone of the chains of unsaturated polyester thermosets of different compositions based on dicyclopentadiene, isophthalic acid, epoxy vinyl ester, and terephthalic acid. The radiolysis is imminent irrespective of the degree of crosslinking in the thermosets both in neat resins and in the presence of solvents. Electron Paramagnetic Resonance (EPR) results show the formation of the alkoxyl radicals and C-centered radicals as the primary intermediate products of the C-O-C scissions. While the alkoxyl radicals of these resins exhibit very good stability even six months after the irradiation, the C-centered radicals decay very rapidly via their reactions with oxygen that is available either as adsorbed in the resins, dissolved in solvents or from the environment. The radiolytically produced ^•OH radicals in the unsaturated-ester aqueous solutions play a major role in inducing scissions on the backbone of the polymer chains. The solvated electrons (e_s) from organic solvents, such as dimethyl sulfoxide and isopropyl alcohol, also induce direct scission of the C-O-C bonds, giving rise to the formation of alkoxyl radicals and C-centered radicals. However, a considerable fraction of e_s is scavenged by the dissolved O₂ to produce O₂⁻. Despite the radiation-induced scissions, irradiation of the resins at a dose level of 1000 kGy results in an increase of the glass transition temperature, T_g. This is due to the simultaneous radiation-induced polymerization of the vinyl monomers, toluene, and styrene that are present in the resins. The increase in T_g is observed in all the resins except for the terephthalic polyester resin in aqueous solution, in which the absence of these monomers results in T_g decreasing sharply with irradiation. This work demonstrates that ionizing radiation triggers continuous free radical-chain reactions that lead to the formation of recyclable oligomers.

Original language	English
Article number	110307
Journal	Polymer Degradation and Stability
Volume	211
DOIs	https://doi.org/10.1016/j.polymdegradstab.2023.110307
State	Published - May 2023

Funding

Research was sponsored by the Laboratory Director's R&D Program of Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy . J.W. was supported by the U.S. DOE Office of Science, Division of Chemical Sciences, Geosciences and Biosciences under contract DE-SC0012704 to Brookhaven National Laboratory . Research was sponsored by the Laboratory Director's R&D Program of Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy. J.W. was supported by the U.S. DOE Office of Science, Division of Chemical Sciences, Geosciences and Biosciences under contract DE-SC0012704 to Brookhaven National Laboratory. *Certain commercial materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

Funders	Funder number
U.S. Department of Energy
National Institute of Standards and Technology
Office of Science
Oak Ridge National Laboratory
Chemical Sciences, Geosciences, and Biosciences Division	DE-SC0012704
UT-Battelle

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10.1016/j.polymdegradstab.2023.110307

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title = "On the electron beam-induced degradation of vinyl ester thermosets",

abstract = "We have demonstrated that electron beam radiolysis induces scissions of the C-O-C bonds along the backbone of the chains of unsaturated polyester thermosets of different compositions based on dicyclopentadiene, isophthalic acid, epoxy vinyl ester, and terephthalic acid. The radiolysis is imminent irrespective of the degree of crosslinking in the thermosets both in neat resins and in the presence of solvents. Electron Paramagnetic Resonance (EPR) results show the formation of the alkoxyl radicals and C-centered radicals as the primary intermediate products of the C-O-C scissions. While the alkoxyl radicals of these resins exhibit very good stability even six months after the irradiation, the C-centered radicals decay very rapidly via their reactions with oxygen that is available either as adsorbed in the resins, dissolved in solvents or from the environment. The radiolytically produced •OH radicals in the unsaturated-ester aqueous solutions play a major role in inducing scissions on the backbone of the polymer chains. The solvated electrons (es) from organic solvents, such as dimethyl sulfoxide and isopropyl alcohol, also induce direct scission of the C-O-C bonds, giving rise to the formation of alkoxyl radicals and C-centered radicals. However, a considerable fraction of es is scavenged by the dissolved O2 to produce O2−. Despite the radiation-induced scissions, irradiation of the resins at a dose level of 1000 kGy results in an increase of the glass transition temperature, Tg. This is due to the simultaneous radiation-induced polymerization of the vinyl monomers, toluene, and styrene that are present in the resins. The increase in Tg is observed in all the resins except for the terephthalic polyester resin in aqueous solution, in which the absence of these monomers results in Tg decreasing sharply with irradiation. This work demonstrates that ionizing radiation triggers continuous free radical-chain reactions that lead to the formation of recyclable oligomers.",

author = "Lorelis Gonz{\'a}lez-L{\'o}pez and Kearney, {Logan T.} and Chris Janke and Wishart, {James F.} and Naskar, {Amit K.} and Nihal Kanbargi and Bateman, {Fred B.} and Mohamad Al-Sheikhly",

note = "Publisher Copyright: {\textcopyright} 2023 Elsevier Ltd",

year = "2023",

month = may,

doi = "10.1016/j.polymdegradstab.2023.110307",

language = "English",

volume = "211",

journal = "Polymer Degradation and Stability",

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T1 - On the electron beam-induced degradation of vinyl ester thermosets

AU - González-López, Lorelis

AU - Kearney, Logan T.

AU - Janke, Chris

AU - Wishart, James F.

AU - Naskar, Amit K.

AU - Kanbargi, Nihal

AU - Bateman, Fred B.

AU - Al-Sheikhly, Mohamad

PY - 2023/5

Y1 - 2023/5

N2 - We have demonstrated that electron beam radiolysis induces scissions of the C-O-C bonds along the backbone of the chains of unsaturated polyester thermosets of different compositions based on dicyclopentadiene, isophthalic acid, epoxy vinyl ester, and terephthalic acid. The radiolysis is imminent irrespective of the degree of crosslinking in the thermosets both in neat resins and in the presence of solvents. Electron Paramagnetic Resonance (EPR) results show the formation of the alkoxyl radicals and C-centered radicals as the primary intermediate products of the C-O-C scissions. While the alkoxyl radicals of these resins exhibit very good stability even six months after the irradiation, the C-centered radicals decay very rapidly via their reactions with oxygen that is available either as adsorbed in the resins, dissolved in solvents or from the environment. The radiolytically produced •OH radicals in the unsaturated-ester aqueous solutions play a major role in inducing scissions on the backbone of the polymer chains. The solvated electrons (es) from organic solvents, such as dimethyl sulfoxide and isopropyl alcohol, also induce direct scission of the C-O-C bonds, giving rise to the formation of alkoxyl radicals and C-centered radicals. However, a considerable fraction of es is scavenged by the dissolved O2 to produce O2−. Despite the radiation-induced scissions, irradiation of the resins at a dose level of 1000 kGy results in an increase of the glass transition temperature, Tg. This is due to the simultaneous radiation-induced polymerization of the vinyl monomers, toluene, and styrene that are present in the resins. The increase in Tg is observed in all the resins except for the terephthalic polyester resin in aqueous solution, in which the absence of these monomers results in Tg decreasing sharply with irradiation. This work demonstrates that ionizing radiation triggers continuous free radical-chain reactions that lead to the formation of recyclable oligomers.

AB - We have demonstrated that electron beam radiolysis induces scissions of the C-O-C bonds along the backbone of the chains of unsaturated polyester thermosets of different compositions based on dicyclopentadiene, isophthalic acid, epoxy vinyl ester, and terephthalic acid. The radiolysis is imminent irrespective of the degree of crosslinking in the thermosets both in neat resins and in the presence of solvents. Electron Paramagnetic Resonance (EPR) results show the formation of the alkoxyl radicals and C-centered radicals as the primary intermediate products of the C-O-C scissions. While the alkoxyl radicals of these resins exhibit very good stability even six months after the irradiation, the C-centered radicals decay very rapidly via their reactions with oxygen that is available either as adsorbed in the resins, dissolved in solvents or from the environment. The radiolytically produced •OH radicals in the unsaturated-ester aqueous solutions play a major role in inducing scissions on the backbone of the polymer chains. The solvated electrons (es) from organic solvents, such as dimethyl sulfoxide and isopropyl alcohol, also induce direct scission of the C-O-C bonds, giving rise to the formation of alkoxyl radicals and C-centered radicals. However, a considerable fraction of es is scavenged by the dissolved O2 to produce O2−. Despite the radiation-induced scissions, irradiation of the resins at a dose level of 1000 kGy results in an increase of the glass transition temperature, Tg. This is due to the simultaneous radiation-induced polymerization of the vinyl monomers, toluene, and styrene that are present in the resins. The increase in Tg is observed in all the resins except for the terephthalic polyester resin in aqueous solution, in which the absence of these monomers results in Tg decreasing sharply with irradiation. This work demonstrates that ionizing radiation triggers continuous free radical-chain reactions that lead to the formation of recyclable oligomers.

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U2 - 10.1016/j.polymdegradstab.2023.110307

DO - 10.1016/j.polymdegradstab.2023.110307

M3 - Article

AN - SCOPUS:85150257792

SN - 0141-3910

VL - 211

JO - Polymer Degradation and Stability

JF - Polymer Degradation and Stability

M1 - 110307

ER -

On the electron beam-induced degradation of vinyl ester thermosets

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