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Xia N.,Northwest University, China | Guo K.,Northwest University, China | Guo K.,Shaanxi Engineering Research Center for Agricultural Equipment | Chen X.,Northwest University, China
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2015

Natural fiber plastic composites (NFPCs) have been given considerable interest by researchers in recent years because of the increasing price of petroleum, ecological concerns, and the impending depletion of fossil fuels. NFPC is a product which can be made from natural fibers (such as wood, cotton stalk, kenaf, jute and banana fiber) and plastics (such as high density polyethylene, polypropylene, polyvinyl chloride and thermoset plastics). In order to use cotton stalk resource effectively and make high performance straw-based composites, this paper presented a potential use of long cotton stalk bundles as matrices and isotactic polypropylene (iPP) films as adhesives for the fabrication of oriented cotton stalk-polypropylene film boards (OCPBs). Firstly, the long cotton stalk bundles were oven-dried, modified by polymeric methylene diphenyl diisocyanate (PMDI) resin, and then divided into 2 equal portions. Each portion formed into a single unidirectional layer and was pre-pressed at room temperature. Then, the pre-pressed layers and iPP films were stacked to form a mat on a stainless steel caul with a wooden mold frame. The plastic films were placed between the pre-pressed layers and on the outside surfaces of the mat. The number of iPP films introduced at each layer was adjusted according to the targeted film content in that panel. Another caul was placed on top of the mat after forming, and 2 mold-releasing papers were used to prevent adhesion between the mat and the caul. Finally, the formed mat was hot-pressed between 2 steel plates preheated to a certain temperature, and then consolidated to the desired thickness. The whole process was program-controlled. After reaching the final thickness and maintaining for a certain duration, the mat was gradually cooled to room temperature. The pressed panel was then trimmed to a panel size of 300 mm×300 mm×10 mm with a density of 0.7 g/cm3. The tested specimens were made according to GB/T 17657 (2013) standards. The effects of film content (5%, 10%, 15%, 20% and 25%), hot pressing temperature (165, 175, 185, 195 and 205℃), hot pressing time (11, 13, 15, 17 and 19 min) and density (0.5, 0.6, 0.7, 0.8 and 0.9 g/cm3) on the properties of OCPBs including modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB) and thickness swelling (THS) were evaluated. The optimum results of the single-factor experiment were further optimized by an orthogonal experiment (L9 (3, 4)). The interface between cotton stalk fibers and iPP films was also investigated by a scanning electron microscope. Results showed that the optimal hot pressing parameters were the following: film content was 15%, hot pressing temperature was 185℃, hot pressing time was 15 min, and density was 0.7 g/cm3. The MOE, MOR, IB and THS of the boards reached 60.60, 5 074.4, 1.48 MPa and 2.53%, respectively. The properties of OCPBs satisfied the requirements of OSB/2 standard. Scanning electron micrographs showed that cotton stalk fibers were compressed and deformed during hot pressing, and wrapped with molten plastics. A mechanical interlock structure between cotton stalk fibers and iPP films was also observed, and that would be the main reason to effectively improve the mechanical properties and thickness swelling of the composite panels. The study can be a reference for fabricating NFPCs with agricultural biomass and plastic film as raw materials. © 2015, Chinese Society of Agricultural Engineering. All right reserved. Source


Yang J.-X.,Northwest University, China | Cui M.,Northwest University, China | Li X.-S.,Northwest University, China | Li X.-S.,Shaanxi Engineering Research Center for Agricultural Equipment
Modern Food Science and Technology | Year: 2014

In this study, electrical impedance tomography was used to detect a foreign body in yoghurt. It was found that variations in the size of the foreign body, applied current, and current frequency showed corresponding changes in the reconstructed image. A 16-electrode data acquisition system was established to obtain image data using an adjacent excitation/measurement scheme. The Modified Newton-Raphson algorithm was applied to reconstruct the image data, binarization was performed for post-processing of the reconstructed images, and a quantitative analysis was performed by comparing the deviations of both the coordinates and area of the images with those of the actual foreign body. The results showed that this method could detect plastic foreign objects within yoghurt, but could not determine the location and shape of the foreign body accurately. In addition, this method was sensitive to the size of the foreign body, but only within a certain range. Optimum detection was possible within a detecting region diameter of 100 mm, under the following conditions: 25 mm size of the foreign body, 15 mA current, and 30 kHz current frequency. Although some details of the original reconstructed image might be lost with this processing method, the image obtained allowed for easier observation and convenience in comparison of imaging results under different conditions. Source


Li X.,Northwest University, China | Li X.,Shaanxi Engineering Research Center for Agricultural Equipment | Xu G.,Northwest University, China | Huang L.,Northwest University, China | And 3 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2015

Plant growth regulators were used frequently to improve the yield of kiwifruits in recent years. But the use of plant growth regulators often caused low internal quality and deformity of fruits, and the expanded kiwifruits easily decay after softening. It is necessary to explore the effect of plant growth regulators on kiwifruit tissue during the ripening process. Up to now, the traditional chemical methods and the other modern techniques such as NIR, FTIR and NMR have been adopted to analyze the influence of plant growth regulators on fruit tissues. But these approaches are difficult to achieve fast and cheap measurement. Electrical impedance spectroscopy (EIS) is a fast developing method in analyzing materials' characterization. When currents with different frequencies flow through the biological tissue, cytomembrane, the extracellular and intracellular fluid would show different electrical properties. Therefore, EIS has the potential to be used for detecting the change of kiwifruit cell microstructure during the ripening process. To develop a quick, convenient and economic method for exploring the effect of plant growth regulators on kiwifruit fruit, EIS technique was used to analyze the change of biological tissue at cellular level during the ripening process of the expanded and control kiwifruits by using an equivalent electrical circuit. Hayden model was chosen to analyze kiwifruit ripening process, which is composed of extracellular resistance, intracellular resistance and constant phase element representing the cytomembrane. Complex nonlinear least square (CNLS) method was used for fitting the EIS data and determining the parameters of Hayden model. The results indicated that the impedance magnitude of the expanded and control fruits decreased with increasing frequency, and impedance magnitude decreased with kiwifruit ripening only at low frequencies. It was obvious during the ripening process that the impedance of control fruits decreased more quickly than that of the expanded fruits. The phase angles of two types of kiwifruits increased sharply and then decreased quickly with the increase of frequency, and reached the maximum values at 12 kHz. Cole-cole plots of kiwifruit tissues presented the semicircles with different radiuses, which represent the characteristics of typical biological tissue. Cytomembrane impedances of expanded kiwifruits changed minimally during the ripening process of 15 days, but after 7 days, cytomembrane impedances of the control fruits dropped sharply. Extracellular fluid resistance of two types of kiwifruits initially decreased, then increased and finally decreased with ripening process. Extracellular fluid resistance of expanded fruits was larger than that of control fruits, and extracellular fluid resistance of control fruits dropped more quickly than that of expanded fruits after 7 days. Variation of intracellular fluid resistance of two types of kiwifruits was not obvious. Because plant growth regulator could alleviate the damage of cell membrane, EIS properties of two types of kiwifruits were different. So electrical impedance spectroscopy is useful for the identification of expended kiwifruits from untreated kiwifruits by impedance properties. Consequently use of EIS to analyze the ripening process provides a technological foundation for the detection of expanded fruits. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved. Source


Xia N.,Northwest Agriculture and Forestry University | Chen X.,Northwest Agriculture and Forestry University | Guo K.,Northwest Agriculture and Forestry University | Guo K.,Shaanxi Engineering Research Center for Agricultural Equipment
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2015

Wood plastic composites were widely used in furniture, infrastructure and transportation area and most of them were made of short fiber and plastic powder. In order to use cotton stalk resources effectively and make high performance straw-based composites, this paper presents a potential use of long cotton stalk bundles as matrix and isotactic polypropylene (iPP) film or high density polyethylene (HDPE) film as adhesive for oriented cotton stalk-plastic boards (OCPB). The polydiphenylmethane diisocyanate (PMDI) resin was added to enhance the interfacial bonding between cotton stalks and plastic films. The long cotton stalk bundles were first oven-dried, resinated by PMDI resin and divided into two equal portions, the cotton stalks and plastic films were then stacked to form a mat. The plastic films were placed between the two portions of cotton stalks and on the outside surfaces of the mat. Number of plastic films used was adjusted according to the targeted film content in that panel. The formed mat was then hot-pressed between two steel plates preheated to 185℃, and consolidated to a desired thickness. After reaching the final thickness and maintaining for 10 min, the mat was gradually cooled to room temperature. The pressed panel was then trimmed to a final panel size of 300 mm×300 mm × 10 mm. The tested specimens were made according to the referred standards. The effects of film contents on the properties of OCPB, including modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB), thickness swelling (THS) and water absorption (WA) were evaluated. The properties of OCPB were compared with that of medium density fiberboard (MDF) and particleboard. Significance test of film contents on the properties of composites was evaluated by SPSS. Results showed that the mechanical and water absorption properties of OCPB made of iPP film were better than that of HDPE film. The best mechanical and water absorption properties of the composites were obtained with the use of 15% iPP film, with the MOE, MOR, IB, THS and WA were 60.60 MPa, 5074.4 MPa, 1.48 MPa, 2.53% and 18.60% respectively. The mechanical and water absorption properties of OCPB were better than that of MDF and particleboard at the film content of 15%. The SPSS test showed that film contents had a significant influence on the properties of OCPB. Scanning electron micrographs showed that there was a mechanical interlock structure between cotton stalk fibers and plastic films. The OCPB could be a good alternative as construction materials used in indoor or outdoor environment. The study could also be a reference for the use of agricultural biomass and plastic film as raw materials for the fabrication of wood plastic composites. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved. Source


Gu R.,Northwest Agriculture and Forestry University | Guo K.,Northwest Agriculture and Forestry University | Guo K.,Shaanxi Engineering Research Center for Agricultural Equipment | Qi C.,Northwest Agriculture and Forestry University | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2010

In order to enhance utilization value of konjak powder and develop environment-friendly wood adhesive, konjac glucomannan and chitosan were blended as main raw bonding materials with adding polyvinyl alcohols (PVA). Thermal characteristics of the blending adhesive were analyzed to determine the hot-pressing temperature parameters by differential scanning calorimetry (DSC). Then the orthogonal experiment was used to investigate the effects of the process parameters on the bonding strength of plywood. The bonding strength of plywood using the konjak powder - chitosan blending adhesive was compared with PVA and without PVA, and the microstructure of the blending adhesives were also analyzed by infrared spectroscopy (FTIR) and scanning electron microscope (SEM). Results showed that the plywood could reach the maximum value of bonding strength when the press temperature, press pressure, pressing time, and adhesive storage time was 130°C, 4 MPa, 15 min and 24 h, respectively. FTIR showed that there existed the strong interaction of hydrogen bond among the three kinds of molecular. SEM observations indicated that the blending adhesive with PVA had the net-like structure so as to increase its whole bonding strength. These results could provide scientific basis for accelerating process of the development of environmentally friendly wood adhesive and improving the processing condition. Source

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