Synthesis, performance and structure characterization of glyoxal-monomethylolurea-melamine (G-MMU-M) co-condensed resin

In order to reduce the formaldehyde emission of formaldehyde-based wood adhesive from the source,it is aimed to develop a novel co-condensed resin of glyoxal-monomethylolurea-melamine(G-MMU-M).A series of G-MMU-M resins with various formulations of raw materials were successfully prepared.The basic properties and bonding performance of the G-MMU-M resins were determined.Furthermore,the structures of resins were characterized by FTIR,^(13)C NMR,XPS,and ESI-MS.The results show that the prepared G-MMU-M resin remains stable for 30 d,meanwhile,the dry and wet bonding strength of the plywoods bonded with the resins,solid content and viscosity are influenced greatly by the addition amount of melamine and MMU/G molar ratio.The G-MMU-M resins with MMU/G molar ratio of 0.9:1.0 and 8% melamine exhibit the highest dry and bonding strength of 1.98 MPa and 1.27 MPa,increased by 34% and 63%,respectively,in comparison with glyoxal-monomethylolurea(G-MMU)resin.In the G-MMU-M resins,there were four main oligomers including M—CH(—^(+)CH-MMU)-O-MMU,M-CH(—CH_(2)OH)-MMU-O-MMU,M—CH(—OH)—^(+)CH-MMU-O-MMU,and M—CH(—^(+)CH-MMU)-MMU-p-G.

An efficient corrosion inhibitor of cassava starch graft copolymer for aluminum in phosphoric acid

Starch is one of the richest natural polymers with low-cost,non-toxic and biodegradable,but is seldom directly used as corrosion inhibitor due to its poor inhibitive ability and low water solubility.To solve this problem,cassava starch-acryl amide graft copolymer(CS-AAGC)was prepared through grafting acryl amide(AA)with cassava starch(CS),and it was firstly examined as an efficient inhibitor for 1060 aluminum in 1.0 mol·L^(-1)H_(3)PO_(4) media.The adsorption behavior of CS-AAGC and its electrochemical mechanism were investigated by weight loss and electrochemical methods.Additionally,the inhibited aluminum surface was fully characterized by a series of SEM,AFM,contact angle measurements and XPS.Results confirm that CS-AAGC performs better inhibitive ability than CS,AA or CS/AA mixture,and the maximum inhibition efficiency of 1.0 g·L^(-1)CS-AAGC is 90.6%at 20℃.CS-AAGC acts as a mixed-type inhibitor while mainly retards the anodic reaction.EIS has three time constants,and the polarization resistance is significantly increased in the presence of CS-AAGC.The micrograph of inhibited aluminum surface is of hydrophobic nature with low surface roughness and little corrosion degree.

Red tetrazolium as an effective inhibitor for the corrosion of cold rolled steel in 7.0 mol·L^(-1) H_2SO_4 solution

The corrosion inhibition of cold rolled steel(CRS) in 7.0 mol·L^(-1) H_2 SO_4 solution by red tetrazolium(RTZ) was carefully investigated using both experimental procedures and theoretical techniques. The results show that RTZ acts as an effective inhibitor for the corrosion of CRS in 7.0 mol·L^(-1) H_2SO_4, and the maximum inhibition efficiency is higher than 95% with a RTZ concentration of 2.0 mmol·L^(-1). The adsorption of RTZ on CRS surface follows Langmuir isotherm. RTZ effectively retards both cathodic and anodic reactions, and acts as a mixed-type inhibitor. EIS exhibits two capacitive loops, and their resistances increase drastically in the presence of RTZ. SEM and AFM confirm that the addition of RTZ could significantly retard the corrosion of CRS surface. A series of characterizations like FTIR, RS, XRD and XPS reveal that the corrosion CRS surface is composed of the corrosion products of iron sulfates, iron oxides and iron hydroxide, as well as inhibitor. Theoretical results of quantum chemical calculation and molecular dynamics(MD) indicate that the adsorption center of RTZ+(organic cationic part of RTZ) mainly relies on its tetrazole ring,and the adsorption of RTZ+on Fe(001) surface is in a nearly flat orientation mode.

“新农科”背景下林业院校植物化学实验教学改革与实践

在“新农科”背景下,结合林业院校植物化学实验教学中存在的普遍问题,从教材建设、教学内容、教学方法、实验室建设等方面进行改进与实践,以便更好地提升教学水平和质量,进一步提高学生的综合能力,为应用型人才的培养打下基础。

Influence of Annealing Atmosphere on Varistor Property of TiO₂-Nb₂O₅-SrCO₃Ceramics

Varistor ceramics are typical electronic ceramics, which are widely used in circuits of overvoltage protection, high voltage stabilization and high energy surge absorption. TiO2 varistor ceramics has the advantages of low varistor voltage and good dielectric properties, but their low nonlinearity limited the application. The influence of annealing on the varistor properties of TiO2-Nb2O5-SrCO3 ceramics was investigated in this paper. TiO2-Nb2O5-SrCO3 varistor ceramics were prepared by the traditional method of ball grinding-forming-sintering and they were annealed in oxygen and nitrogen, respectively. The nonlinear coefficient α and the breakdown voltage EB of the samples were tested using the varistor dc parameter meter. The microstructure of samples was analyzed by XRD, SEM, STEM-EDAX and SAEDP. The results show that during annealing, Sr2+ ions with a larger radius obtain the kinetic energy and are segregated to grain boundaries, which increases the acceptor density of the grain boundaries and improves α. Annealing in an oxygen atmosphere, the enrichment of oxygen at grain boundaries is also helpful to increase the density of acceptor states and the height of the potential barrier, so as to further increase α. Meanwhile, annealing makes crystalline grains grow properly, which results in even grain size, reduces the porosity and increases the density of grains. So EB tends to reduce. As the doping concentration of Nb2O5 and SrCO3 is 0.15 mol%, respectively, and sintering temperature is 1300°C, TiO2-Nb2O5-SrCO3 varistor ceramics annealed in oxygen for 3 h at 750°C achieved the highest nonlinear coefficient α = 8.9 and the lowest breakdown voltage EB = 19.1 V·mm-1, which annealed in nitrogen achieved α = 8.4, EB = 20.6 V·mm-1, both superior to unannealed samples.