TG-DTA study of melamine-urea-formaldehyde resins

The thermal behaviour of MUF resins from different suppliers with different content of melamine was studied, along with the ¹³C NMR spectroscopic analysis of resin structure and the testing of particleboards in current production at Estonian PB factory Pärnu Plaaditehas AS. The chemical structure of resins from DMSO-d₆ solutions was analysed by ¹³C NMR spectroscopy on a Bruker AMX500 NMR spectrometer. The melamine level in different MUF resins is compared by the ratios of carbonyl carbon of urea and triazine carbon of melamine in ¹³C NMR spectra. Curing behaviour of MUF resins was studied by stimultaneous TG-DTA techniques on the Labsys? instrument Setaram. The shape of DTA curves characterisises the resin synthesis procedure by the extent of polymerisation of UF and MF components and is in accordance with structural data.     

Synthesis and thermal properties of the thermosetting resin based on cyano functionalized benzoxazine

A novel thermosetting resin based on cyano functionalized benzoxazine (BZCN) has been synthesized from 2,6-bis(4-diaminobenzoxy)benzonitrile phenol and formaldehyde by solution reaction. The structure of the monomer is supported by FTIR, ¹H NMR and ¹³C NMR spectra, which have exhibited that the reactive benzoxazine rings and cyano group exist in the molecular structure of BZCN. The curing reactions of BZCN are monitored by the disappearance of the nitrile peak and the tri-substituted benzene ring that is attached with oxazine ring peak at 2231 and 930 cm⁻¹, respectively. The complete cured materials could achieve char yields up to 70% at 800 °C in nitrogen atmosphere, above 64% at 600 °C in air (20% oxygen) environments and the glass transition temperature up to 250 °C. The thermally activated curing polymerization reaction of BZCN follows multiple polymerization mechanisms via the ring-opening polymerization of oxazine rings and the triazine ring-formation of cyano groups, which contribute to the stability of the polymer.     

废铬革屑的综合回收利用

碱法水解铬鞣废革屑得到的胶原蛋白灰分含量较高,达不到产品质量标准。针对此问题,利用较为廉价的氧化钙作碱性试剂处理废铬革屑,确定了最优实验方案:碱用量为6%,反应温度为85℃,反应时间为6h。在此基础之上,进一步研究了降低胶原灰分含量的方法:对革屑进行预处理,将胶原液静置过夜过滤除杂,并以不同用量的离子交换树脂处理,当其用量为革屑质量的20%时可使灰分含量降低到国家标准。从水解残余物铬饼中制得了商品氧化铬和硫酸铬,提高了废革屑的利用价值,减少了环境污染。     

Microencapsulated ammonium polyphosphate with urea–melamine–formaldehyde shell: preparation,characterization, and its flame retardance in polypropylene

Microencapsulated ammonium polyphosphate (MCU‐APP) with urea–melamine–formaldehyde (UMF) resin is prepared by in situ polymerization, and is characterized by FTIR and XPS. The microencapsulation of APP with the UMF resin leads to a decrease in the particle's water solubility. The flame retardant actions of MCU‐APP and APP in PP are studied using limiting oxygen index (LOI) and UL‐94 test, and their thermal stability is evaluated by thermogravimetric analysis. It is found that the LOI value of the PP/MCU‐APP composite is higher than the value of the PP/APP composite. In comparison with the PP/MCU‐APP composites, the LOI values of the PP/MCU‐APP/DPER ternary composites at the same additive loading increase, and UL‐94 ratings of most ternary composites are raised to V‐0. The water‐resistant properties of the PP composites containing APP and MCU‐APP are studied. Moreover, the combustion behavior of the PP composites is investigated by the cone calorimeter. Copyright © 2008 John Wiley & Sons, Ltd.     

Ultrasound monitoring of the cure kinetics of an epoxy resin: Identification,frequency and temperature dependence

In this paper the monitoring of ultrasonic parameters of a thermosetting resin during an isothermal curing process is described. The ultrasonic properties are studied within the context of the monitoring of composite plate production by resin transfer molding (RTM). These ultrasonic characteristics can be related directly to cure kinetic models. An ultrasonic method, based on the measurement of the elastic constant and associated mechanical loss has been developed to identify the variations of the phase transformation. To study the reaction kinetics, the time dependence of the elastic coefficient is modeled using a Weibull distribution. The approximate time derivative form of this Weibull model makes it possible to find the relationship between ultrasonic parameters and the chemical Kamal model. The ultrasonic monitoring of a cooling process was also performed to study the temperature sensitivity after curing. Thanks to experimental measurements of the ultrasonic velocity and attenuation, the power law coefficient variations and their temperature sensitivity can be examined. The resulting viscoelastic Cole-Cole parameters were estimated and a frequency-temperature (f, T) model was proposed.     

Gas chromatography/mass spectrometry characterization of historical varnishes of ancient Italian lutes and violin

The organic constituents of historical vanishes from two ancient Italian lutes and a Stradivari violin, kept in the Musée de la musique in Paris, have been characterized using gas chromatography-mass spectrometry. Results have been compared with the chromatograms and mass spectra of recent as well as old naturally aged reference materials. The three historical varnishes analyzed have been shown to be oil varnishes, probably mixtures of linseed oil with resins. Identification of diterpenoids and triterpenoids compounds, and of the resins that may have been ingredients of the varnishes, are discussed in this paper.     

Validation of the concentration profiles obtained from the near infrared/multivariate curve resolution monitoring of reactions of epoxy resins using high performance liquid chromatography as a reference method

This paper reports the validation of the results obtained by combining near infrared spectroscopy and multivariate curve resolution-alternating least squares (MCR-ALS) and using high performance liquid chromatography as a reference method, for the model reaction of phenylglycidylether (PGE) and aniline. The results are obtained as concentration profiles over the reaction time. The trueness of the proposed method has been evaluated in terms of lack of bias. The joint test for the intercept and the slope showed that there were no significant differences between the profiles calculated spectroscopically and the ones obtained experimentally by means of the chromatographic reference method at an overall level of confidence of 5%. The uncertainty of the results was estimated by using information derived from the process of assessment of trueness. Such operational aspects as the cost and availability of instrumentation and the length and cost of the analysis were evaluated. The method proposed is a good way of monitoring the reactions of epoxy resins, and it adequately shows how the species concentration varies over time.     

氯磺化聚乙烯/聚甲基丙烯酸丁酯/环氧树脂三组分IPNs的合成与表征

采用同步-分步结合的方法合成了氯磺化聚乙烯/聚甲基丙烯酸丁酯/环氧树脂(CSM/PB-MA/EP)三组分IPNs.先用同步法合成CSM/EP二组分IPNs作为骨架网络,再将PBMA溶胀进入骨架网络中.得到三组分IPNs.网络间经两次相互缠结贯穿后,比单独用同步法或分步法合成的IPNs对网络间束缚作用大,且骨架网络与PBMA组成比较接近时,相容性较好.TEM结果表明:用分步染色方法可以观察三相间的形态变化和相区尺寸的相对大小.     

Isothermal curing of an epoxy resin by alternating differential scanning calorimetry

The quasi-isothermal curing of a diepoxide resin with a triamine of polyoxypropylene was studied by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The complex heat capacity measurements allows to analyse the vitrification process at curing temperatures (T_c) below the maximum glass transition of the fully cured epoxy (T_g∞=85.8°C). Initially, the modulus of the complex heat capacity, |C^*_p|, increases until a maximum (conversion between 0.42 and 0.56) and then decreases. This step is followed by an abrupt decay of |C^*_p|, due to the vitrification of the system, which allows the determination of the vitrification time. This value agrees well with that determined by the partial curing method. The phase angle and out-of-phase heat capacity show an asymmetric wide peak during the vitrification process. The change in |C^*_p| at vitrification decreases with the increase of T_c becoming zero at temperature T_g∞. This epoxy-triamine system shows a delay of the vitrification process respect to other model epoxy systems probably due to the presence of polyoxypropylene chains in the network.

The decay of |C^*_p| during vitrification may be normalised between unity and zero by defining a mobility factor. This mobility factor has been used to simulate the reaction rate during the stage where the reaction is controlled by diffusion. The observed reaction rate is simulated by the product of the kinetic reaction rate, determined by the autocatalytic model, and the mobility factor.     

Changes in poly-vinylidene fluoride produced by electron irradiation

A study was made of the effects of electron irradiation of poly-vinylidene fluoride, using the DSC, FTIR, and X-ray techniques, as well as determining the percent cross-linking. Changes in crystallinity and melting point of the sample as a function of dose were found, the latter due to competition between cross-linking and crystallinity. The cross-linking was observed to increase with radiation dose. Chemical changes observed include the formation of carbonyl groups and double bonding, associated with the loss of HF.