低温烘烤酸固化氨基醇酸木器底漆的制备

采用丁醇醚化脲醛树脂与蓖麻油和大豆油改性短油度醇酸树脂在酸催化下低温烘烤进行交联形成的共聚氨基醇酸木器底漆。该木器涂料的性能良好,打磨性好,干燥快、抗咬筋效果好,研究了影响涂膜性能的主要因素。     

木粉疏水改性对HDPE基木塑复合材料性能的影响

采用一种操作简便且易于工业推广的方法对木粉进行疏水改性,具体过程为：将3种可热聚合的单体,即甲基丙烯酸甲酯（MMA）、甲基丙烯酸丁酯（BMA）和苯乙烯（St）均匀喷洒在木粉上,经过预热处理后,与配方中其他组分,如高密度聚乙烯（HDPE）和马来酸酐接枝聚乙烯（MAPE）等通过高速混合机混合均匀,采用双螺杆挤出机造粒后,注射制备木塑复合材料（WPC）样条,测试其力学性能。另外,考察了疏水改性对WPC接触角、维卡软化温度、洛氏硬度、吸水性能、热性能的影响规律。结果表明：疏水改性后WPC的接触角增大,木粉和HDPE的界面相容性改善,力学性能得到明显提高。其中,当MMA、BMA和St的添加量为3%时,WPC的力学性能最好,与疏水改性前相比,弯曲强度分别提高了17.3%、26.3%和27.5%,弯曲模量分别提高了24.4%、24.4%和26.0%,冲击强度分别提高了54.7%、57.7%和60.5%。 此外,疏水改性后WPC的维卡软化温度、洛氏硬度、耐水性和耐热性也得到改善。     

Aliphatic polyesters as models for relaxation processes in crystalline polymers: 3. Mechanical relaxation in copolymers of adipic acid with 1,6 and 2,5-hexanediols

The shear moduli of a series of the title polyesters spanning a crystallinity range of 0–60% have been measured as a function of temperature at ≈1 Hz using a torsion pendulum. The experimental isochronal temperature scans of G′ and G″ are fitted to phenomenological equations. With only minor adjustments, the same relaxation spectrum parameters as found dielectrically for these polymers (relaxation shape, central relaxation times) fit the mechanical data. Thus, for the β (glass—rubber) relaxation in the amorphous fraction the broadness is very sensitive to the presence of the crystal fraction and becomes increasingly broad as the degree of crystallinity increases. In contrast, the γ process dynamic behaviour is insensitive to the presence of and degree of crystallinity. Unrelaxed and relaxed moduli values are determined for the γ and β processes. A composite model approach is used to determine bounds on the amorphous-phase unrelaxed and relaxed γ and β moduli from the bulk specimen values. As was the case dielectrically, the γ process, in addition to being assigned to the amorphous fraction, has a strength that depends on the diol composition also. The relaxed (γ + β) amorphous-phase rubbery shear modulus is bound reasonably well from application of the composite model to the bulk specimen values and is assigned the value 100 ± 20 MPa at 250 K. It decreases relatively strongly with increasing temperature.     

Mechanical and thermal properties,morphology and relaxation characteristics of poly(lactic acid) and soy flour/wood flour blends

Poly(lactic acid) (PLA) is a biodegradable polymer derived from sugar‐based materials, and its applications are varied. PLA blends are commonly employed to overcome certain disadvantages such as poor impact strength, low heat distortion temperature, poor processability and relatively high cost. In this study, blending PLA with soy flour (SF), wood flour (WF) and sodium bisulfite‐modified SF was used to improve the adhesion to PLA. In all cases, 0.5 wt% methylenediphenyl diisocyanate (MDI) was used as a coupling agent. Mechanical and thermal properties, morphology and relaxation characteristics of the blends were investigated. The results showed that MDI was an effective coupling agent for the WF/PLA system in improving tensile strength and elongation. Differential scanning calorimetry results indicated that SF and modified SF act as nucleation agents and facilitate the crystallization behavior of PLA by increasing the percentage crystallinity. From mechanical relaxation of the temperature‐variant system, we determined how the mechanical relaxation time evolves during the course of heating and obtained the Kohlrausch–Williams–Watts parameter and activation energy (ΔE). PLA and its blends exhibited highly homogeneous relaxational dynamics in their transition from glass to liquid, and ΔE of PLA and its blends is mainly affected by their densities and compositions. Copyright © 2010 Society of Chemical Industry     

Mechanical and thermal properties of poplar wood polyacrylonitrile composites

Wood polyacrylonitrile composite (WPC) from poplar wood was synthesized. The synthetic process was carried out through benzoyl peroxide (0.05 mol l^?1) catalyzed impregnation polymerization of acrylonitrile (6.075 mol l^?1) into poplar wood in benzene medium at 70 ± 1 °C. Modification of the properties of WPC over untreated wood was evaluated in terms of compression, impact strength and simultaneous differential thermogravimetry‐thermogravimetric‐differential thermal analysis (DTG‐TG‐DTA) in air. Compression, impact strength and resistance of wood against thermo‐oxidation were improved with impregnation of polyacrylonitrile. Impregnation of polyacrylonitrile into poplar wood was ascertained through UV‐vis spectroscopy and scanning electron microscopy. Copyright © 2004 Society of Chemical Industry     

Mechanical relaxation mechanism of epoxide resins cured with diamines

The mechanism of mechanical relaxation, which is observed between 50° and 90°C in epoxide resins cured with aromatic and alicyclic diamines, has been investigated by comparing dynamic mechanical properties and chemical structures of these networks. This relaxation is denoted here as the α′ relaxation. The occurrence of the α′ relaxation depends on the existence of p-phenylene groups, and is independent of the degree of cure in the cured epoxide resins. Moreover, the intensity of the α′ relaxation increases linearly with increasing the concentration of p-phenylene groups in the networks. From these results, it is concluded that the α′ relaxation of the cured epoxide resins is attributed to the motion of p-phenylene groups in the network structures.     

水性木器涂料的低温施工问题和解决方法

对水性木器涂料在低温条件下施工遇到的问题进行分析,通过与施工人员沟通协调对产品和施工进行调整,解决了企业水性木器涂料产品的低温施工问题。     

Low-temperature Maxwell-Wagner relaxation in (Na + Nb) co-doped rutile TiO2 colossal permittivity ceramics

The exact mechanism of the stunning colossal permittivity behavior found in (donor-acceptor) co-doped TiO₂ system still remains enigmatic. This behavior results from a thermally activated dielectric relaxation occurring below 50 K. Herein, thermally stimulated depolarization current analysis combined with dielectric investigation was used to disentangle this relaxation in (Na + Nb) co-doped TiO₂ ceramics. We find that this relaxation is related to frozen electrons and features the Vogel-Fulcher behavior and negative dielectric tunability. Our results reveal that this low-temperature relaxation is a new kind of Maxwell-Wagner relaxation. Differences between the low-temperature Maxwell-Wagner relaxation and its high-temperature counterpart are discussed. This study provides new insights into the physics of the eye-catching dielectric properties in co-doped TiO₂ system.     

核磁共振波谱在木材改性中的应用

核磁共振技术与其他方法无法比拟的优势在木材改性中起到了重要的作用,综述了1H NMR,13C NMR,29S i NMR,31P NMR和19F NMR的基本原理,以及它们在木材三大素及其改性、木材改性中的应用。     

钛石膏的改性处理和力学性能研究

采用破碎、干燥、粉磨、煅烧和陈化等处理工艺对钛石膏进行物理改性,研究了煅烧温度对钛石膏力学性能的影响,通过掺加硫酸钠、生石灰和硅酸盐水泥等外加剂对钛石膏进行化学改性,确定了外加剂掺加量的最佳配比,并对改性机理进行了探讨.结果表明,钛石膏经180 ℃煅烧3 h,掺加0.5%硫酸钠、3%生石灰和5%硅酸盐水泥,制得的试样力学性能可以达到:2 h抗折强度2.6 MPa、抗压强度3.2 MPa,绝干抗折强度4.58 MPa、抗压强度5.2 MPa.经改性后钛石膏试样的强度指标可以达到建筑石膏国家标准中1.6等级的要求.     

Mechanical properties and morphology of impact modified polypropylene–wood flour composites

The mechanical properties and morphology of polypropylene/wood flour (PP/WF) composites with different impact modifiers and maleated polypropylene (MAPP) as a compatibilizer have been studied. Two different ethylene/propylene/diene terpolymers (EPDM) and one maleated styrene–ethylene/butylene–styrene triblock copolymer (SEBS–MA) have been used as impact modifiers in the PP/WF systems. All three elastomers increased the impact strength of the PP/WF composites but the addition of maleated EPDM and SEBS gave the greatest improvements in impact strength. Addition of MAPP did not affect the impact properties of the composites but had a positive effect on the composite unnotched impact strength when used together with elastomers. Tensile tests showed that MAPP had a negative effect on the elongation at break and a positive effect on tensile strength. The impact modifiers were found to decrease the stiffness of the composites. Scanning electron microscopy showed that maleated EPDM and SEBS had a stronger affinity for the wood surfaces than did the unmodified EPDM. The maleated elastomers are, therefore, expected to form a flexible interphase around the wood particles giving the composites better impact strength. MAPP further enhanced adhesion between WF and impact-modified PP systems. EPDM and EPDM–MA rubber domains were homogeneously dispersed in the PP matrix, the diameter of domains being between 0.1–1 μm. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1503–1513, 1998     

Studies on dielectric relaxation in ceramic multiferroic Gd1−xYxMnO3

Dielectric study over a broadband was carried out from 10 to 70 K on ceramic Gd_1?xY_xMnO₃ (x=0.2, 0.3 and 0.4). For all the compositions, a prominent sharp peak about ~18 K was observed in the temperature dependence of both ε′(T) and ε″(T) at all frequencies, indicating a long‐range ferroelectric (FE) transition. Using Cole‐Cole fit to the permittivity data, the relaxation time τ and the dielectric strength ?ε were estimated. Temperature variation of τ(T) in the Arrhenius representation is found to be nonlinear (non‐Debyean relaxation), with increasing barrier‐activation energy over successive temperature‐windows. Interestingly, for all the compositions, we witness a jump in τ(T) about the ferroelectric transition temperature, concurred by a broad‐maximum in ?ε(T),signifying the critical slow down of relaxations near long‐range FE‐correlations.     

基于仿生学的木材超疏水表面改性研究进展

介绍了超疏水理论模型及天然超疏水表面仿生机制;综述了国内外关于木材超疏水表面的构建方法,包括模板印刷法、刻蚀法、接枝共聚法、溶胶-凝胶法等,分析了不同超疏水表面构建方法的优缺点及存在的问题,并阐述了超疏水木材的应用前景;最后,对超疏水木材研究中存在的一些问题及未来的发展趋势进行了总结与展望.     

Biodegradable,superhydrophobic walnut wood membrane for the separation of oil/water mixtures

The preparation of environmentally friendly oil/water separation materials remains a great challenge. Freeze-drying of wood after lignin removal yields wood aerogels, which can be used as substrates to prepare fluorine-free environmentally friendly superhydrophobic materials, However, they are more suitable for absorption rather than filtration applications due to their poor strength. A study using cross-sections of pristine wood chips as substrates retains the original strength of wood, but the use of the cross-sectional of wood pieces limits their thickness, strength, and size. In this paper, a degradable fluorine-free superhydrophobic film (max. water contact angle of approximately 164.2°) with self-cleaning and abrasion resistance characteristics was prepared by a one-step method using pristine and activated walnut longitudinal section films as the substrate, with tetraethyl orthosilicate as a precursor and dodecyltriethoxysilane as a modifier. The tensile strength results show that superhydrophobic films with pristine or activated wood substrates maintained the strength of pristine wood and were 2.2 times stronger than the wood aerogel substrate. In addition, after cross-laminating the two samples, the films had the ability to separate oil and water by continuous filtration with high efficiency (98.5%) and flux (approximately 1.3 × 10³ L∙m^‒2∙h^‒1). The method has potential for the large-scale fabrication of degradable superhydrophobic filtration separation membranes.     

Determination of moisture content and moisture content profiles in wood during drying by low-field nuclear magnetic resonance

In this article, the low-field nuclear magnetic resonance was used to measure the moisture content (MC) and MC profiles in poplar wood during real-time drying. The T₂ distribution curve at each drying stage measured using the Carr–Purcell–Meiboom–Gill pulse sequence provided detailed information in the dynamic change of free water as well as bound water of the whole wood sample. In addition, a new developed SE-SPI pulse sequence was first used to evaluate the spatially resolved T₂ distribution of the successive nondestructive sliced layer of wood. Combined with the area integration method, the moisture content in each layer was calculated, and the change of MC profiles within wood at the MC above and below fiber saturation point was well reflected.     

Mechanical properties of teak wood flour‐reinforced HDPE composites

Mechanical properties such as tensile and impact strength behavior of teak wood flour (TWF)‐filled high‐density polyethylene (HDPE) composites were evaluated at 0–0.32 volume fraction (Φ_f) of TWF. Tensile modulus and strength initially increased up to Φ_f = 0.09, whereas a decrease is observed with further increase in the Φ_f. Elongation‐at‐break and Izod impact strength decreased significantly with increase in the Φ_f. The crystallinity of HDPE also decreased with increase in the TWF concentration. The initial increase in the tensile modulus and strength was attributed to the mechanical restraint, whereas decrease in the tensile properties at Φ_f > 0.09 was due to the predominant effect of decrease in the crystallinity of HDPE. The mechanical restraint decreased the elongation and Izod impact strength. In the presence of coupling agent, maleic anhydride‐grafted HDPE (HDPE‐g‐MAH), the tensile modulus and strength enhanced significantly because of enhanced interphase adhesion. However, the elongation and Izod impact strength decreased because of enhanced mechanical restraint on account of increased phase interactions. Scanning electron microscopy showed a degree of better dispersion of TWF particles because of enhanced phase adhesion in the presence of HDPE‐g‐MAH. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

高分子聚合物松弛行为及模型的研究进展

高分子聚合物材料作为一种使用频率高且应用范围广的材料,其松弛行为对于其加工制品的精度具有重要的影响,且高分子化学合成的结果会最终影响高分子聚合物的松弛行为。由此总结了高分子聚合物松弛行为的特点,整理了其力学松弛及模型、松弛时间的研究进展。并由此提出现阶段高分子聚合物的松弛行为研究的局限性,并指出未来的研究方向。     

水性聚氨酯木器涂料改性研究进展

水性聚氨酯木器漆具有良好的性能，是目前水性木器漆研发的一个热点和重点。介绍了单组分水性聚氨酯涂料和双组分水性聚氨酯涂料的制备和性能，综述了水性聚氨酯木器涂料的改性研究进展。     

Aliphatic polyesters as models for relaxation processes in crystalline polymers: 4. Dielectric relaxation in oriented specimens

To investigate further the effect of the crystal phase on amorphous-phase relaxation, samples of 6-6, 5–7, and 6–10 polyesters have been oriented by extrusion in the solid-state through a tapered die and the dielectric constant and loss measured both parallel and perpendicular to the extrusion direction. The data have been analysed quantitatively in terms of the Cole—Cole phenomenological equation and relaxation times, width parameters and relaxation strengths determined. For the β (glass—rubber relaxation) the relaxation times are shifted 2–3 orders of magnitude to longer times and the relaxation is broadened slightly compared to the unoriented polymers. There also tends to be reduction of overall parallel and perpendicular relaxation strength for the β process on orientation. The γ processes show little effect of orientation on relaxation time and width and do not show reduction of overall relaxation strength. These observations are consistent with crystal displacement further restricting amorphous-phase longer-range segmental motion (β process) but having little effect on the locallized motions associated with the γ process. Both the γ and β processes show anisotropy in relaxation strength. The anisotropy is analysed with a newly developed theory to separate inherent phase anisotropy from apparent anisotropy due to composite or form effects. The average angle made by the lamellar surface normal to the extrusion direction enters as a parameter in the theory. Measurements of relaxed specimen $\text{ε}{}_{\mathrm{}}$ and ε_⊥ values for both the γ and β processes serve to determine both f_a the amorphous-phase orientation function and the average tilt angle for the specimens here. This is possible because for the γ process relaxation strength is small and specimen anisotropy is dominated by inherent phase anisotropy but for the γ + β processes larger relaxation strength leads to specimen anisotropy being strongly influenced by crystal—amorphous phase composite effects. Values of f_a are in the range of 0.05–0.20 for specimens with f_c in the range 0.5–0.9. Indicated lamellar tilt angles are in the range of 24°–80°.     

硅橡胶及其玻璃布复合体低温力学性能的研究

研究了低苯基硅橡胶（ ＭＰＱ１２０ － １） 硫化胶及其玻璃布复合体在－ １００ ℃～２５ ℃温度区间内的力学性能,发现在结晶温度附近,硫化胶及其复合体的拉伸强度和扯断伸长率分别达到最高和最低值。硅橡胶的低温结晶使硫化胶回弹性迅速降低。