Properties of crosslinked waterborne polyurethane adhesives with modified melamine: Effect of curing time, temperature, and HMMM content

A series of crosslinked waterborne polyurethane (WBPU) adhesives were prepared by prepolymer synthesis. Modified melamine, hexamethoxymethyl melamine (HMMM) was used as the crosslinking agent. It was elucidated by FTIR and ¹H-NMR spectroscopy that the crosslinking reaction occurred between the polyurethane carboxyl acid salt groups and the HMMM methoxy groups. The hydrophobicity of the WBPU films increased after HMMM crosslinking. As the HMMM content was increased (increasing mole ratio of HMMM/dimethylol propionic acid (DMPA)), the water uptake (%) of the film decreased, and the water contact angle increased. The thermal stability, tensile strength, and initial modulus increased with increasing HMMM content up to an optimum value (mole ratio of HMMM/DMPA=0.5) at which point the maximum thermal stability, tensile strength, and initial modulus were recorded. The adhesive strength was found to be dependent on HMMM content, curing time, and temperature. The adhesive strength of crosslinked WBPU in the case of optimum HMMM content (8.46 wt%) was only slightly affected after immersing adhesive bonded nylon fabrics in water (for up to 2 days).     

Properties of waterborne polyurethane (WBPU) coatings: Effect of alkyl chain length of tertiary amines of carboxylic acid salt groups

Waterborne polyurethane (WBPU) dispersions were prepared via a pre-polymer process using 4,4-dicyclohexylmethane diisocyanate (H₁₂MDI), poly(tetramethyleneoxideglycol) (PTMG), 2,2-dimethylol propionic acid (DMPA), ethylene diamine (EDA), and tertiary amines (TAs) with varying amounts of DMPA and TAs. Three TAs with different alkyl chain lengths were used to neutralize the DMPA carboxylic group: N,N-dimethylbutylamine (DMBA, C4), N,N-dimethylhexylamine (DMHA, C6), and N,N-dimethyloctylamine (DMOA, C8). The structures of the synthesized WBPUs were determined via FT-IR and ¹H NMR spectroscopic techniques. The effects of DMPA and TA content and the TA alkyl chain length on stability of dispersions and properties such as water swelling (%), glass transition temperature (T _g ), tensile strength, binding energy and adhesive strength were investigated. The initial adhesive strength of the intact coatings increased with increasing DMPA and TA content and increasing alkyl chain length of TA. However, after immersion of the coatings in water, the adhesive strength decreased. The maximum adhesive strength under water was observed at a DMPA content of 20.20 mol% with 5.30 wt% DMOA, which has the longest alkyl chain.     

Preparation and properties of waterborne polyurethanes based on triblock glycol (CL)4.5-PTMG-(CL)4.5 for water vapor permeable coatings: Effect of soft segment content

A series of waterborne polyurethanes (WBPU) were prepared from 4,4-dicyclohexylmethane diisocyanate (H₁₂MDI), 2,2-bis(hydroxylmethyl) propionic acid (DMPA), ethylenediamine (EDA), triethylamine (TEA), and triblock glycol [TBG, (ε-caprolactone)_4.5-poly(tetramethylene ether) glycol (MW=2000)-(ε-caprolactone)_4.5: (CL)_4.5-PTMG-(CL)_4.5, MW=3000] as a soft segment. Two melting peaks of TBG at about 14°C and 38°C were observed indicating the presence of two different crystalline domains composed of CL and PTMG dominant component. The effect of soft segment content (60–75 wt%) on the colloidal properties of dispersion, and thermal and mechanical properties of WBPU films, the water vapor permeability (WVP) and water resistance (WR) of WBPU-coated Nylon fabrics, and the adhesive strength of WBPU-coated layer and Nylon fabrics was investigated. As soft segment contents increased, the water vapor permeability of WBPU-coated Nylon fabrics increased from 3615 to 4502 g/m²day, however, the water resistances decreased from 1300 to 500 mmH₂O.     

Effect of ionizing and non-ionizing preirradiations on physico-mechanical properties of coir fiber grafting with methylacrylate

Coir fibers were modified with methyl acrylate (MA) mixed with methanol (MeOH) under thermal curing method at different temperatures (40?C80 °C) for different curing times (20?C60 min). A series of solutions of different concentrations of MA in methanol along with 2 % benzoyl peroxide, were prepared. Monomer concentration, curing temperature, and curing time were optimized with the extent of grafting of monomer and mechanical properties of cured fiber and found to be 30 % MA, 60 °C and 40 min curing time registered as better performance (Grafting (Gr) = 5.7 %, tensile strength (TS) = 72 %, elongation at break (Eb) = 88 %) than those of untreated fiber. For further improvement of the properties, untreated coir fibers were pretreated with gamma and UV radiations at different doses and then pretreated fibers were soaked in the optimized monomer and cured under optimum conditions. Coir fiber pretreated with UV radiation and grafted with optimized monomer showed the best properties such as Gr (7.12 %), TS (132 %), and Eb (153 %) over raw fiber. Water uptake and simulated weathering test of untreated and treated coir fibers were studied.     

Banana fiber-reinforced polypropylene composites: A study of the physico-mechanical properties

Banana fiber-reinforced polypropylene (PP) matrix composites were prepared by compression molding and their mechanical properties were evaluated. Banana fibers and matrices were irradiated with UV radiation at different intensities. Mechanical properties of irradiated banana fibers and matrices based composites were found to increase significantly compared to untreated counterparts. Optimized banana fibers were treated with 2-hydroxyethyl methacrylate (HEMA) solution and were cured in an oven at different temperatures for different curing times and then composites were fabricated. Monomer concentration, curing temperature and curing time were optimized with the extent of polymer loading and mechanical properties and showed better mechanical properties over untreated composites. Water uptake and simulating weathering test of the composites were also investigated.     

Optimization of curing process for polymer-matrix composites based on orthogonal experimental method

In this paper, the orthogonal experimental method was carried out to optimize the curing process of aeronautical composite X850/T800 in autoclave process. Four important curing parameters including curing pressure, heating rate, curing temperature and heat preservation time were taken into account, and sixteen samples were fabricated to study the effects of the four parameters mentioned above on the curing quality by interlaminar properties test and microstructure analysis. The interlaminar properties and the interfacial bonding quality of these samples were studied by the short-beam three points bending test and scanning electron microscopy, respectively. Results revealed that the optimal curing process of X850/T800 composite laminate should be as follows: curing pressure of 0.6 MPa, heating rate of 1.5 °C/min, curing temperature of 160 °C, and heat preservation time of 120 min.     

Treatment of Cotton by β-Cyclodextrin/Triclosan Inclusion Complex and Factors Affecting Antimicrobial Properties

The efficacy of antimicrobial treatment of cotton fabrics depends on various parameters of the coating process, such as the chemical nature and concentration of the antimicrobial agent, the composition of the crosslinking formulation, and the curing temperature. The inclusion complex of triclosan with β-cyclodextrin (βCD) was synthesized and characterized by FTIR, XRD, NMR, Raman, SEM, and TGA. The minimum inhibitory concentration and minimum bactericidal concentration of the complex against Klebsiella pneumoniae and Staphylococcus aureus were compared to those of its precursor. A multifactorial study included an evaluation of the effects of triclosan complexation with β-cyclodextrin, a comparison between the glyoxal and tetracarboxylic acid as crosslinkers, an investigation of the effect of crosslinker and catalyst concentrations, and a comparison of curing at 120°C and 180°C. The cotton was characterized by FTIR-ATR, the micrographs of treated samples were obtained by SEM and the weight add-on was calculated. The bactericidal properties were determined according to AATCC-147. The correlation between the coating process parameters and the antimicrobial efficacy was determined. The optimal combination leading to the highest weight add-on and the antimicrobial coating that was most durable to multiple detergent washes at an elevated temperature was the use of complexed triclosan grafted onto the cotton in the presence of tetracarboxylic acid, followed by curing at 180°C. The curing temperatures were 120°C (P=0.002) and 180°C (P=0.008), catalysts were 1 % and 2 % aluminium sulfate and sodium hypophosphite (P<0.001), and the crosslinkers were 5 % and 10 % glyoxal and butanetetracarboxylic acid (P<0.001); these parameters significantly enhanced the antimicrobial properties of the treated fabrics. The study showed that βCD did not have antimicrobial activity, while the βCD/triclosan-treated textile exhibited potential antimicrobial properties. Overall, the bactericidal activity of fabrics can be enhanced by using βCD/triclosan with 10 % butanetetracarboxylic acid as a cross-linker and 5 % sodium hypophosphite as a catalyst at a curing temperature of 180°C.     

微波辐射凝固胶清橡胶性能的研究

将微波辐射应用于胶清橡胶的凝固,对比微波辐射凝固胶清橡胶(NR-s-m)与硫酸凝固胶清橡胶（NR-s-a）的性能差异。结果表明,理化性能方面,NR-s-m的灰分含量、杂质含量、挥发物含量以及氮含量较高,塑性初值、抗氧指数和门尼粘度也更高;力学性能方面,NR-s-m硫化胶拉伸强度、扯断伸长率、撕裂强度和硬度均比NR-s-a的高;硫化特性方面,NR-s-m比NR-s-a的硫化速度快,并随微波辐射功率的增大而加快。     

Preparation of Epoxy Shape Memory Polymers for Deployable Space Structures Using Flexible Diamines

In order to develop epoxy shape memory polymers (ESMPs) with high switching temperature and excellent toughness for deployable space structures, the crosslink density and chain flexibility of candidate ESMP samples were tunned by adding two flexible poly(oxypropylene) diamines, Jeffamine D-230 (D230) and Jeffamine D-400 (D400), as a secondary curing agent. The desired switching temperature of ESMPs for deployable space structures was set within the range of 120-135°C. By adding D230 and D400, the switching temperature of the ESMPs could be adjusted to within this range by increasing their crosslink density, and their impact strength could be significantly increased due to the stress relaxation properties of the diamines’ flexible molecular chains. The modulus and tensile strength of the ESMPs increased, but elongation at break decreased, in proportion to the diamine content. The ESMPs with a suitable switching temperature for deployable space structures had a high elongation at break greater than 22 % and good shape recovery and shape fixity ratios. The larger the value of shape recovery ratio, the faster the shape recovery speed.     

促进剂ZDiBC对硫化天然胶乳性能影响的研究

二异丁基二硫代氨基甲酸锌（ZDiBC）因其分子中二异丁胺的支化结构产生的空间位阻作用,使其与通用的未支化同类超促进剂相比在硫化过程中可显著降低N-亚硝基胺类物质的生成,是一种高效、制得硫化胶力学性能良好的环保型促进剂。而ZDiBC对硫化天然胶乳的胶体性能研究未见有报道。本研究采用硫磺为硫化剂,以ZDiBC为天然胶乳硫化促进剂,并与胶乳工业常用的二乙基二硫代氨基甲酸锌（ZDC）作对比研究,考察促进剂的用量、胶乳硫化温度和贮存时间对硫化天然胶乳粘度、机械稳定度、热稳定度的影响。结果表明：ZDiBC对硫化天然胶乳的粘度和机械稳定度的影响大于ZDC,对热稳定度的影响相差不大;随胶乳硫化温度的增加以ZDiBC和ZDC为促进剂的硫化胶乳粘度升高,而硫化胶乳机械稳定度和热稳定度则降低;随贮存时间的延长硫化胶乳的粘度增加,且ZDiBC为促进剂的硫化胶乳粘度增加幅度大于ZDC,硫化胶乳的机械稳定度略有增加而其热稳定度呈下降的趋势。     

The effect of gelation and curing temperatures on mechanical properties of pultruded kenaf fibre reinforced vinyl ester composites

Process parameters such as gelation and curing temperatures are parameters that influence the pultruded kenaf reinforced vinyl ester composites profile quality and performance. The effect of gelation and curing temperatures on mechanical (tensile, flexural and compression properties) and morphological properties of pultruded kenaf reinforced vinyl ester composites were analyzed. Obtained results indicated that increase of gelation and curing temperatures during the pultrusion process of kenaf reinforced vinyl ester composites influenced the mechanical properties of the composites. When the gelation and curing temperatures were increased, tensile strength, tensile modulus, flexural strength, flexural modulus and compressive strength were affected and they were either increased or decreased. The factors that influenced these results include improper curing, excessive curing, water diffusion, and the problems associated with interfacial bonding between fibre and matrices. The optimum values of the tensile strength for gelation and curing temperatures of kenaf pultruded composites were at 100 °C and 140 °C, tensile modulus at 80 °C and 180 °C, flexural strength at 100 ° and 140 °, flexural modulus at 120 ° and 180 °, and compressive strength at 120 °C and 180 °C, respectively. The scanning electron micrographs of tensile fractured samples clearly show that with the increase in gelation temperature, it creates the lumens between matrix and kenaf fibre thus reducing tensile properties whereas increasing the curing temperature caused less fibre pull out and enhanced fibre/matrix interfacial bonding.     

Effect of coir fiber content and compatibilizer on the properties of unidirectional coir fiber/polypropylene composites

The main objective of this research was to study the effect of fiber content variation and stearic acid (SA) treatment on the fundamental properties of unidirectional coir fiber (CF) reinforced polypropylene (PP) composites. Several percentages of filler contents were used (10–40 wt %) in order to gain insights into the effect of filler content on the properties of the composites. Coir/PP composites were fabricated by compression molding, and the properties of composites were studied by physico-mechanical and thermal properties. The results from mechanical properties such as tensile strength (TS), tensile modulus (TM) and impact strength (IS) of the CF/PP composites were found to be increased with increasing fiber content, reached an optimum and thereafter decreased with further increase in fiber content. Treatment of the coir with SA as the coupling agent enhanced the mechanical properties, crystallization temperature and crystallinity of virgin PP and water desorption of the resulting composites, resulting from the improved adhesion between the CF and PP matrix. Scanning electron micrographs (SEM) of the tensile fractured samples showed improved adhesion between fiber and matrix upon treatment with SA. Interfacial shear strength (IFSS) of the composites was measured by single fiber fragmentation test (SFFT).     

2-巯基苯并噻唑制备的恒粘天然橡胶加工性能的研究

采用2-巯基苯并噻唑制备恒粘天然橡胶（MBT-CVNR）,并与盐酸羟胺制备的恒粘天然橡胶（HH-CVNR）进行对比,采用橡胶加工分析仪并结合交联密度、硫化特性、分子量、门尼粘度和凝胶含量研究加速贮存前后恒粘剂对天然橡胶(NR)加工性能的影响,同时探究交联密度、硫化特性、分子量、门尼粘度和凝胶含量与加工性能之间的关系。结果表明：加速贮存前,加入恒粘剂后,NR的交联密度、分子量、门尼粘度、凝胶含量和弹性模量都减小,损耗因子增大;加速贮存后,NR和HH-CVNR的交联密度、分子量、门尼粘度和凝胶含量都出现增大趋势,NR增大最多,流动性明显变差,加工性能最差,而MBT-CVNR几乎没有变化,加工性能受影响不大。     

Insulation rigid and elastic foams based on albumin

Albumin-based rigid and elastic foams were prepared by mechanically beating water solutions of the protein mixed with formaldehyde and camphor. The resulting foams were cross-linked in a traditional or in a microwave oven. Formaldehyde was used as hardener of the protein and camphor as a plasticizer. Thermal conductivity was tested and found to be acceptable for thermal insulation but did not appear to be influenced by variations in foam density. Scanning electron microscopy of the different formulations showed some differences in cells structure. Formulations of different water content, formaldehyde hardener content, camphor content and oven curing time were tested. Within certain limits (a) increases in water proportion rendered the foam more elastic, (b) higher formaldehyde content increased foam rigidity and strength up to a value beyond which no further increase occurred, (c) the amount of camphor influences markedly the compression strength and foam elasticity/plasticity, (d) curing time improving foam strength up to 5 min in microwave curing, without any further effect for longer heating times. Only addition of glycerol, yielded truly soft elastic foams.     

海南典型农林废弃物生物炭特性分析

原料和裂解温度是影响生物炭属性的重要因子。选取海南椰壳、香蕉假茎、橡胶树枝等9种典型原料,分析其在3个温度下（300、500、700 ℃）真空裂解制备的生物炭属性及其内在关联,结果显示：（1）生物炭pH、碳氢比、比表面积和磷含量随温度升高而增加,而产率、氢和硫含量随温度升高而逐渐降低;碳氮含量、电导率以及钾、钙、镁、阳离子交换量等因原料不同随温度升高变化不一致;重金属含量都不超标。（2）生物炭中碳含量、碳氮比以及磷、钾、钙、镁含量与原料属性呈显著正相关（P<0.05）。原料中钾含量是影响生物炭pH、电导率和阳离子交换量的重要因素。（3）综合考虑产率、含碳量、比表面积、阳离子交换量以及矿质元素等性质,蘑菇渣、椰子壳和香蕉茎生物炭表现最好,本研究可为我国热带地区筛选适宜生物炭原料提供参考。     

Effect of monophenyl borate on properties of high-ortho phenolic fibers

A series of monophenyl borate (MPB) modified high-ortho phenolic copolymer fibers (BOPFs) were prepared by melt-spinning of the high-ortho phenol-formaldehyde resins with different content of MPB, and cured in a formaldehyde solution. The solution curing fibers were heated up to 240 °C at elevated temperatures in N₂. The effect of MPB on the structure and properties of the BOPFs was investigated by Fourier transform infrared spectrometer (FTIR), nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The results show that a B-O linkage inserts into the high-ortho phenolic copolymer molecular chain with the addition of MPB, and increases the crosslinkage and thermal stability. The peak of O/P (ortho/para) value of fiber (1.94) and elongation (5.6 %) were obtained when BOPFs-4 was heat-cured at 240 °C for 2 h.     

香草兰豆荚加工过程物性测定与风味电子感官分析

香草兰豆荚加工过程分为杀青、发汗、干燥和陈化四个阶段,期间豆荚颜色改变并产生香味。为了探究香草兰豆荚加工过程中物理状态变化对生香反应的影响及表征作用,本文对加工四个阶段豆荚水分含量、p H等物理性质进行了检测,并对三种不同处理方式的豆荚进行了感官分析。实验结果表明:鲜豆荚及杀青豆荚为鲜绿色,发汗后的豆荚变为褐色后逐渐变深;杀青豆荚水分含量最高,加工中水分含量逐渐减少,整个加工过程豆荚p H小于5.5且呈降低趋势;鲜豆荚豆腥味较重,陈化后豆荚豆腥味弱而香草味强;电子感官分析结果表明经过冷冻捣碎和加水磨浆处理的豆荚嗅觉和味觉属性均不同,添加香兰素对味觉属性有影响但对嗅觉属性影响较小,煮沸对豆荚味觉属性有影响。     

Soaking Induced Changes in Chemical Composition,Glycemic Index and Starch Characteristics of Basmati Rice

An attempt was made to determine the qualitative changes in basmati rice(Pusa Basmati 1121, PB1121) during soaking at 40 ℃ to 80 ℃. Soaking temperature had significant effect(α = 0.01) on chemical composition, glycemic index and starch characteristics of rice. Starch content, apparent amylose content, crude protein content and crude fat content in un-soaked rice were found to be 73.24%, 27.26%, 8.79% and 2.56%, respectively, but differences in these traits were observed after soaking. Amylose to amylopectin ratio(Am/Ap) decreased from 0.59 to 0.52(soaked at 80 ℃). Crude fibre and crude ash contents increased after soaking. The mineral composition(K, P, S, Ca, Mg, Mn, Fe, Cu and Zn) in soaked rice was found to be 16.46% higher than un-soaked rice at the same degree of polishing. Glycemic index of un-soaked rice was found to be 58.41, but decreased to 54.31 after soaking at 80 ℃. Pasting properties, scanning electron microscope images, and X-ray diffractograms suggested partial gelatinization of starch in the temperature range of 60 ℃ to 80 ℃. Based on qualitative changes in rice(apparent amylose content, Am/Ap ratio and crystallinity rate), it was concluded that intermediate soaking temperatures(60 ℃ to 70 ℃) would be useful for soaking of PB1121.     

Reduced Pressure Curing on Polycarbosilane Precursor for Synthesis of Silicon Carbide Fiber

Low pressure curing method with iodine vapor was used on low softening temperature polycarbosilane (PCS) precursor for fabrication of continuous SiC fiber at relatively low temperature. The low curing temperature can provide with a wide range of softening temperature PCS precursors, especially with low softening PCSs, which have a good spinnability, but many difficulties with conventional oxidation curing method. The low pressure curing method having the presence of iodine vapor have shown the more positive effect on pyrolysis with early stage crystallization of β-SiC at 1300 °C. Crystal size of β-SiC, cured at 0.008 kPa is around 2–3 nm larger than cured at 101 kPa. In addition, the higher tensile strength of SiC fiber at elevated temperature can be obtained at 0.008 kPa with a value of 2.1 GPa, compare to 1.3 GPa at 101 kPa of curing pressure condition.     

Temperature during grain ripening affects the ratio of type-II/type-I protein body and starch pasting properties of rice (Oryza sativa L.)

The starch and protein properties of rice grain are important factors for sake brewing and these properties are reported to be influenced by temperatures during grain ripening. Amylose content, nitrogen content, protein composition, pasting properties measured by a Rapid Visco Analyser (RVA), and their relationship to temperatures during ripening were investigated in a rice cultivar, Yamadanishiki, which was grown under various conditions in the same experimental field. The average temperature after heading was significantly correlated with amylose content and RVA properties, but not with nitrogen content. Under high temperatures during ripening, a decrease in prolamin, which accumulated in type I protein body (PB-I), and an increase in glutelin, which deposits in type II PB (PB-II), were recognized. The ratio of PB-II/PB-I and RVA pasting temperatures were distinctly increased as the temperature became higher. High temperatures during grain ripening would lead to difficulties in digesting steamed rice grains by Aspergillus oryzae, together with ease in digesting rice protein. The average temperature of 11–20 days after heading showed a higher correlation coefficient than that of 1–10 or 21–30 days, implying that temperatures during the middle stage of grain development would be important in determining the rice component that relates to brewing properties.