| Wiht the strengthening of environmental awareness and the increasing depletion of fossilresources, petroleum based polymer packaging materials widely used for now, due to its nonbiodegradability, cause the difficoulty to recycle the waste and can not be compostingeffectivly, which caused great burden to the ecological environment. The bio-plymers fromrenewable resources having the potential to replace petroleum based polymers, become theresearch hotspot of biodegradable packaging materials. But bio-polymers generally haveperformance defects, therefore, modification and applied research is the present main researchdirecitons. Paper based bio-polymer composite material with good application prospect hasobtained more and more attention, and there were many relevant research.Polylactic acid (PLA) is a kind of biological polyester material from renewable resources,wich is fully biodegradable and one of the most promising bio-polymers, with goodcomprehensive performance. PLA coated paper or paperboard is a promising biodegradablepackaging materials. A new method for preparation of PLA composite paper was presented.With the PLA nano particle pigment made through a chemical and mechanical perparationmethod, and aqueous solution of chitosan and polyvinyl alcohol used as the coating adhesiverespectively, PLA coating was prepared. PLA pigment coated paper was perpared, followedby hot rolling or pressing process, and the PLA particles melt to form a continuous coatinglayer on paper, then PLA coated paper obtained. And the properties of the PLA particles andPLA coating were studied.The plasticizing effect of chloroform and the co-solvent wiht ethanol or n-propanol,polyethylene glycol(PEG) and polycaprolactone(PCL) o n polylactic acid coating were studiedin solution coating process. By observation of filming process, thermal performance testing,oxygen permeability, moisture permeability, and the heat sealing tests, it was found that theco-solvent, PEG and PCL lowered glass transition temperature and melting point of PLA layerto different degrees, meanwhile, increased the crystalization of PLA layer somewhat, due tothe crystallization induction. But these factors above have little effect on moisturepermeability, oxygen permeability and the heat sealing property of PLA slution coating paper.PLA particles were prepared through the emulsion solvent evaporation method and nanohomogenization method respectively, and the obtained PLA particles were characterized byfourier transform infrared spectrometer (FT-IR), scanning electron microscopy (SEM) andmalvern particle size analyzer. Emulsion solvent evaporation prepared PLA microparticlesinto porous sphere, wherein, PLA microparticles prepared by the cationic surfactant is of minimum particle size and particle size distribution, maximum yield. Moreover, emulsionsolvent evaporation method can be used to prepare PLA nano particles modified bymontmorillonite. In addition, nano homogenization method can be used for the preparation ofPLA micro-nano particles. By high-speed liquid shear, impact, strong pressure drop inhomogeneous valve put strong effect on high-speed liquid feed, and prepared PLA particlesare solid particles with irregular shape. Finally, the hydrophilic modification of the PLAparticles through ozone treatment was researched, found that surface water wettability of PLAparticles can be improved by ozone treatment in the neutral condition. However, PLAprepared by emulsion solvent evaporation method has good surface water wettalility due toporosity and residual surfactant.Aqueous solution of chitosan and polyvinyl alcohol were used as PLA coating adhesiverespectively, and the PLA composite paper were made by coating and hot pressing method.The polylactic acid coating was characterized using SEM, atomic force microscopy (AFM),FT-IR, differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) and themoisture permeability, oxygen permeability and heat sealing properties of PLA compositepaper were studied. It is feasible to prepare PLA composite paper by coating-hot pressingmethod, and the PLA composite paper has similar properties to PLA solution coating paper.Moreover, the adhesive resin also has some influence on the properties of the P LA coatings.The glass transition temperature and the melting point of PLA layer were decreased indifferent degree, but the crystallinity increased, which is not conducive to a flexible resinlayer. In additon, the coating from different hot press method has different quality. Theorientation effect in micro scale occored in both rolling press process and flatten press process,but, coating with rolling pressing has higher gloss and smoothness, and coating with flattenpressing has poorer gloss and smoothness. For PLA-PVA coating, hot pressing treatmentincreases the crystallinity of resin layer, wihle, it decreases the crystallinity of PLA-chitosancoating. And the annealing treatment can make the crystallization of the two increased, thoughthe barrier properties of coating can be improved, but the coating becomes brittle ductilewhich is not conducive to improving the flexibility of the resin layer.Conducting a comprehensive qualitative and quantitative analysis on the water vaporpermeability behavior of PLA compsite paper, we found water vapor permeability of PLAcomposite paper follow the general rule of multilayer material’s moisture permeability. Basedon this rule, the water vapor transmission rate (WVTR) and coating weight of PLA compositepaper get a good linear fitting results and get the empirical formula. Moreover, since the basesheet has a decisive influence on the properties of the mixed layer formed between the resin and the base paper, the impact of properties of the base paper on paper-plastic compositematerials can not be simply ignored.Finally, the degradation behavior of PLA composite paper in paper recycling process wasstudied. Under the action of water, heat, crushing, rubbing in process of bleaching anddeinking of secondary fiber, the PLA coating was substantially completely degraded, andthe end products are water and carbon dioxide which avoid stickies problems existing in fiberregeneration process of ordinary paper-plastic composite materials, therefore, having no effecton the papermaking process. |
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