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Abstract
Because discarded polystyrene (PS) is little affected by degrading agents, PS was treated with a remote microwave (MW) plasma discharge of an Ar/O2 mixture in the absence of radiation to increase wettability and introduce functional groups which make the waste more liable to degradation and useful for technological applications. X-ray photoelectron spectroscopy (XPS) detected decreases in the aromatic sp2 and aliphatic sp3 carbons with treatment and, initially, increases in C–O and carbonyl groups, present in the formation of ethers, epoxides, alcohols, ketones and aldehydes. At longer treatment times, ester, O–C=O; carbonate-like, O–(C=O)–O; and anhydride, O=C–O–C=O; moieties are observed with an overall oxygen saturation level of 23.6 ± 0.9 at% O. Atomic Force Microscopy (AFM) measurements detected little change in surface roughness with treatment time. Advancing water contact angle decreased by ca. 50% compared to pristine PS indicating an increase in hydrophilicity because of oxidation. Washing the treated samples in deionized water decreased the oxygen concentrations at the saturation treatment times down to 18.6 ± 1 at% O due to the washing away of a weak boundary layer.
Highlights
IntroductionSince polystyrene (PS, Figure 1) has limited water adsorption, and physical and chemical properties that make it relatively non-biodegradable [1], pretreatment of its surface is often done to increase wettability and introduce reactive functional groups to enhance degradation and usefulness for technological applications [2,3].Technologies 2018, 6, 21; doi:10.3390/technologies6010021 www.mdpi.com/journal/technologiesLtd. www.tandfonline.com [4].www.tandfonline.com [4].One way to increase the hydrophilicity of the PS surface is to use vacuum UV (VUV)One way to increase hydrophilicity of the PS surface is to vacuumtoUV (VUV) photo-oxidation photo-oxidation where athe remote microwave (MW)plasma is use employed produce excited atoms, where a remote microwave plasma is employed to produce excited atoms, such as Ar (which such as Ar (which emits 104.8 and 106.7 nm VUV radiation), which is photo-absorbed by emitsVUV radiation), which is photo-absorbed by gaseous oxygen flowing gaseous oxygen flowing over the PS surface [4]
Oxygen and sometimes a trace amount of nitrogen were detected on the surface of Carbon, oxygen and sometimes a trace amount nitrogen detected the surface every every PS sample
The treatment of PS with O atoms in the absence of radiation showed a controlled increase in the concentration of oxygen with treatment time up to a saturation level of 23.6 ± 0.9 at % O compared to ca. 20 at % observed by VUV photo-oxidation [4]
Summary
Since polystyrene (PS, Figure 1) has limited water adsorption, and physical and chemical properties that make it relatively non-biodegradable [1], pretreatment of its surface is often done to increase wettability and introduce reactive functional groups to enhance degradation and usefulness for technological applications [2,3].Technologies 2018, 6, 21; doi:10.3390/technologies6010021 www.mdpi.com/journal/technologiesLtd. www.tandfonline.com [4].www.tandfonline.com [4].One way to increase the hydrophilicity of the PS surface is to use vacuum UV (VUV)One way to increase hydrophilicity of the PS surface is to vacuumtoUV (VUV) photo-oxidation photo-oxidation where athe remote microwave (MW)plasma is use employed produce excited atoms, where a remote microwave plasma is employed to produce excited atoms, such as Ar (which such as Ar (which emits 104.8 and 106.7 nm VUV radiation), which is photo-absorbed by emitsVUV radiation), which is photo-absorbed by gaseous oxygen flowing gaseous oxygen flowing over the PS surface [4]. One way to increase the hydrophilicity of the PS surface is to use vacuum UV (VUV). One way to increase hydrophilicity of the PS surface is to vacuumtoUV (VUV) photo-oxidation photo-oxidation where athe remote microwave (MW). Plasma is use employed produce excited atoms, where a remote microwave plasma is employed to produce excited atoms, such as Ar (which such as Ar (which emits 104.8 and 106.7 nm VUV radiation), which is photo-absorbed by emits. The oxidation of VUV the surface occur because oxygen molecules oxygen in the regionmay of the electromagnetic spectrum [5],photo-absorb resulting in in the region of the electromagnetic spectrum [5], resulting in photo-dissociation photo-dissociation forming reactive ground state, P, and electronically excited, D and 1S, forming oxygen.
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