Physical and chemical changes in feather keratin during pyrolysis

The structural changes of chicken feather fibers (CFF) were investigated during pyrolysis by thermal analysis techniques coupled with mass spectrometry, solubility tests and gel permeation chromatography. The experimental data showed simultaneous disulfide bond cleavage and peptide crosslinking reactions, and suggested the dependency of crystalline melting on disulfide bond cleavage. The variation in the kinetics of these reactions played an important role in the melting transition and stability. Thus, careful tuning of the pyrolysis thermal profile provided conditions to obtain useful fibrous material at high temperatures. For instance, long-time heat treatments below the melting point provided sufficient crosslinks in the protein matrix to keep the fibrous structure intact. The protein matrix went through a series of transformations including cyclization and aromatization reactions above the melting point. Degradation of the matrix and liberation of aromatic carbons and cyclic amines were observed during these transformations. These pyrolysis mechanisms can serve as a guide for producing materials with desired properties from CFF and other keratin fibers, particularly in textile, high performance composite and catalyst applications.     

Long term environmental effects on physical properties of vinylester composite pipes

Glass fiber reinforced vinylester pipes (GFRP) have been exposed to outdoor conditions for 60 months. The effect of the outdoor exposure on the glass transition temperature (Tg) and the crosslinking index is discussed. The Tg and the degree of crosslinking has been determined using differential scanning calorimetry (DSC). DSC has become a preferred technique for rapid determination of transition temperatures and crosslinking for pure polymers, however, the use of this technique for composites is quite complex. This complexity arises from the fact that, in addition to the temperature overlap between the Tg and that of the crosslinking range, the amount of glass fibers in the GFRP is not constant. For this reason, a special measuring technique has been developed for the measurement of the amount of crosslinking of GFRP material. In this paper, it is illustrated that the DSC results clearly show the glass transition temperature and the exothermic crosslinking reaction of the vinylester composites. The results show that the glass transition temperature of the vinylester rapidly increases with respect to exposure time up to 12 months and then slightly decreases for longer exposure times. Similar trends were also observed for the change of the degree of crosslinking. The outdoor environment has also affected the weight of the exposed GFRP samples. It is observed that the weight of GFRP has gradually decreased with the exposure time. These physical changes of Tg, crosslinking and weight have impact on the tensile strength of the GFRP. For the initial outdoor exposure up to 24 months there is a 12% increase in strength from 250 MPa to 280 MPa. This increase is attributed to about 12% increase in crosslinking of the GFRP. However, for longer exposure the tensile strength has decreased back to 250 MPa due to slight decrease in crosslinking and small reduction of weight. It is observed that most of the weight loss has taken place at the surface of the GFRP samples.     

Preparation and Kinetic Modeling of Cross-Linked Chitosan Microspheres Immobilized Zn(II) for Urea Adsorption

The preparation of Zn(II)-immobilized glutaraldehyde-crosslinked chitosan microspheres which was modified with epichlorohydrin, tetraethylenepentamine, and bromoacetic acid was presented in this work. The Zn(II)-immobilized value of the microspheres (Ac-TEPA-CS) is 43.6 mg g^?1, which is higher than the blank microspheres. The adsorption of urea onto Zn-Ac-TEPA-CS was studied in a batch system. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherm and isotherm constant, and the kinetic of adsorption process were estimated. These data fits well with Langmuir isotherm and also indicated that the adsorption process is exothermic and follow the pseudo-second-order kinetics. The adsorption capacity depends upon the pH, the temperature and the initial concentration of urea. It observed that Zn-Ac-TEPA-CS could be repeatedly used by elution and regeneration without significant loss of adsorption capacity.     

Network characteristics of hydrogenated nitrile butadiene rubber networks obtained by radiation crosslinking by electron beam

The effects of high-energy radiation on hydrogenated nitrile butadiene rubber (HNBR) copolymer structure and properties were studied. Characterization by FTIR spectroscopy, swelling and mechanical measurements of irradiated and un-irradiated sample permit us to correlate the change in structure with properties. The modifications obtained are dependent on the radiation dose of the incident electron beam. FTIR spectroscopy in absorption mode shows that irradiation of HNBR first induces trans-vinylene bond formation and secondly small amounts of carbonyl (CO) groups. Moreover, more significant changes were observed with swelling method and mechanical behaviour showing the effect of crosslinking on the elastomer.     

具有超支化结构的聚醚型脂肪族聚氨酯弹性体的合成与表征及力学性能研究

用聚四氢呋喃醚二醇、端羟基超支化聚酯(HB-20)、异佛尔酮二异氰酸酯和1,4-丁二醇,合成了含有超支化结构的聚醚型脂肪族聚氨酯(PU)弹性体.通过Flory-Rehner公式计算了体系的交联密度;用FT-IR、WAXD和DSC表征了超支化PU的氢键化程度和形态.实验结果表明,在PU弹性体中引入少量的HB-20,能提高氨基甲酸酯羰基的氢键化程度和软硬段间的微相分离程度,从而显著提高材料的拉伸强度.由于氢键化程度和交联密度双重效应的影响,含6 wt%HB-20的聚醚型PU与不含HB-20的PU相比拉伸强度提高了2倍多,达到37.9 MPa,断裂伸长率仍高达414%.     

原位交联明胶电纺纤维的制备工艺研究

提出一种原位交联工艺,用于一步制备交联明胶电纺纤维膜,克服目前该电纺膜交联工艺繁琐以及交联过程破坏纤维形态等缺点.通过一系列实验,找出明胶-三氟乙醇-戊二醛三元溶液体系的稳定电纺条件.所得的纤维直径在1μm左右,远大于单纺明胶的纤维直径.同时发现,在电纺过程中,由于纤维表面戊二醛迅速挥发,使得纤维形成"伪核壳"结构.利用流变仪对三元溶液交联速率进行分析,结果表明戊二醛加入明胶溶液后,体系黏度瞬间增大,10 min后维持稳定.最后,通过耐水性试验评价纤维膜交联效果,发现纤维膜有10%左右的溶解,但在水介质中仍可保持很好的纤维形态.     

Stability of biomimetic ferrofluids established by a systematic study using microwave irradiation at defined wattages

An established biomimetic process for the synthesis of aqueous ferrofluids using polymers has been subjected to systematic microwave irradiation at different wattages primarily to see if the magnetization could be increased by microwave irradiation and if so how would it affect the stability of the fluid. Care has been taken to maintain ambient conditions of synthesis even after three cycles of microwave irradiation before oxidation and ten cycles after it, so as not to violate the basic principles of the process. Detailed characterization using, x-ray diffractometry, transmission electron microscopy, fourier transform infra-red spectroscopy, dynamic light scattering, thermo-gravimetric analysis, differential thermal analysis and vibrating sample magnetometry showed that these fluids containing iron oxide nanoparticles-poly(vinyl) alcohol nanocomposites are highly stable in the proportions established by us. Measurements at five different wattages double the saturation magnetization but the stability remains unaffected compared to the one without microwave irradiation, forcing us to believe that the incubation of the iron salt solution and the polymer in the right proportion before oxidation is what contributes to the stability and that increasing the number of cycles of microwave irradiation at this stage, perhaps, would have led to a more pronounced effect.     

超支化聚乙烯接枝马来酸酐及其过程中交联和降解反应的抑制

采用后过渡金属催化剂二-(2,6-二异丙基苯基)丁二亚胺溴化镍(IBNB),通过均相聚合法合成了高分子量和高支化度的超支化聚乙烯(HBPE).以二特戊基过氧化物(DTAP)为引发剂,研究了HBPE接枝马来酸酐(MAH)反应,并用N,N-二乙基肉桂酰胺(DECA)作为抑制剂,有效地抑制了接枝反应体系中的交联和降解副反应.接枝反应体系中分别加入相同摩尔量的DECA、N,N-二甲基乙酰胺、苯乙烯、3-(2-呋喃)丙烯酸、肉桂酸乙酯,通过比较接枝产物的凝胶含量和分子量,发现DECA抑制交联和降解副反应的效果最好,同时解释了DECA的作用机理.