Surface Modification Of Rice Straw With Plasma Technology

In this doctoral thesis, cold plasma technology was induced to treat rice straw. Treated and control straw samples were compared in chemical groups, elements, and wettability, using Fournier transferred infrared spectra (FTIR), X-ray Photoelectron Spectroscopy(XPS), and KSV sigma70, respectively. Oxygen plasma-treated rice straw was further made into particleboard to test properties. Extensively, application research of rice strawboard was conducted in packaging.The thesis was composed by eight chapters, i.e., (1)Preface, (2)Cold plasma treating process, (3)Surface chemical groups of plasma-treated rice straw, (4) Surface chemical elements of plasma-treated rice straw, (5) Surface wettability of plasma-treated rice straw, (6) Particleboard manufacturing of plasma-treated rice straw, (7) Application trial of rice strawboard, and (8) Conclusions.Conclusions were drawn as follows:Surface protection layer of rice straws were significantly decomposed by plasma, therefore exposing the inner polar chemical groups and chemical elements. Simultaneously, the etched straw surface was chemically grafted. To compare, rice straw has 58.7 per cent of -C-C- and/or -C-H groups with inorganic elements such as Si,K and Na covered inside, while after oxygen plasma treatment, -C-C- and/or -C-H groups concentration decreased to about 22.4 per cent with inorganic substances being exposed outside and considerable polar groups coming up (e.g., -C-O-:12.6%→13.7%;-C=O:4.6%→6.5%;-COOH:2.0%→4.2%;Si:0→8.3%;K:0→1.6%;Na:0→1.4%). Oxygen plasma generating power and treating time were two key treating factors at 5~30Pa vacuum level. The higher power (150W→250W→350W) and/or the longer treating time (3min→5min→7min), the better treating effect. Connection of FTIR and XPS analysis, it was found that rice straw has two protection layers, i.e., a hydrocarbon far outside layer and an adherent inner inorganic layer.Wettability of oxygen plasma-treated rice straw was also improved significantly. At 100~300 watt power level for 1~7min, treated rice straws showed decreasing contact angles against distilled water. The contact angles may increase back continuously in air after plasma treatment: after 24 hours obviously increased, after 7 days, springbacked to about 50o, and 10 days later almost back to the untreated.Oxygen plasma-treated at 200W,7mim, 5~30Pa) rice straw particles were used to make particleboard with UF resin (content: 12% based on oven-dry particles). Results showed evident improvement in physicomechanical properties. MOR and MOE even partially passed national stdandard specifications, and IB strength and TS were bettered. Application of agricultural straws in packaging industry replacing wood is beneficial for environment protection and packaging materials innovation. The poplar-straw composite packaging box designed and trially made for machines packaging in this research were proved technically and economically feasible, which had been accepted by corresponding national administrations.