Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Fabrication of Biodegradable Polyester Nanocomposites by Electrospinning for Tissue Engineering
Zhi-Cai Xing,Seung-Jin Han,Yong-Suk Shin,Inn-Kyu Kang
Journal of Nanomaterials , 2011, DOI: 10.1155/2011/929378
Abstract: Recently, nanocomposites have emerged as an efficient strategy to upgrade the structural and functional properties of synthetic polymers. Polyesters have attracted wide attention because of their biodegradability and biocompatibility. A logic consequence has been the introduction of natural extracellular matrix (ECM) molecules, organic or inorganic nanostructures to biodegradable polymers to produce nanocomposites with enhanced properties. Consequently, the improvement of the interfacial adhesion between biodegradable polymers and natural ECM molecules or nanostructures has become the key technique in the fabrication of nanocomposites. Electrospinning has been employed extensively in the design and development of tissue engineering scaffolds to generate nanofibrous substrates of synthetic biodegradable polymers and to simulate the cellular microenvironment. In this paper, several types of biodegradable polyester nanocomposites were prepared by electrospinning, with the aim of being used as tissue engineering scaffolds. The combination of biodegradable nanofibrous polymers and natural ECM molecules or nanostructures opens new paradigms for tissue engineering applications.
Air Tightness Control of Passenger Car Wheels  [PDF]
Vatroslav Grubisic
Engineering (ENG) , 2017, DOI: 10.4236/eng.2017.92008
Abstract: Since the tubeless tires and especially cast alloy wheels are used, the air tightness of wheels is an important factor of the automobiles quality. Based on specification of the car industry that up to 10% decrease of the prescribed nominal tire pressure during a time of six-month is allowed, the requirements presented in specifications and norms are treated and validated. The practical experience and influences on the wheel tightness control are discussed and the data presented in a report of a wheel manufacturer, concerning the replacements of wheels in service due to air leakage are evaluated. Summarizing the results of analyses, a proposal is made for the testing of the cast aluminum car wheels to meet the requirements for a reliable and economical air tightness control in modern test facilities.
Chemical resistance/thermal and mechanical properties of unsaturated polyester-based nanocomposites
Y. Jaya Vinse Ruban,S. Ginil Mon,D. Vetha Roy
Applied Nanoscience , 2013, DOI: 10.1007/s13204-013-0193-1
Abstract: Nanocomposites were synthesized using unsaturated polyester as the matrix and organically modified montmorillonite (CA-MMT) as the reinforcing agent. XRD pattern of the modified montmorillonite showed that the interlayer spacing expanded from 1.21 to 1.9 nm, indicating intercalation. TGA and DTA show loss of organic surfactant from interlayer galleries. Glass transition temperature (T g) of these composites increased from 71 °C in the unfilled unsaturated polyester to 79 °C in the composites with 5 % organically modified montmorillonite. Chemical resistance and mechanical properties of the UP/organo-clay nanocomposites were studied. Chemical resistance was studied under aqueous conditions in acetic acid, nitric acid, hydrochloric acid, sodium hydroxide, aqueous ammonia and sodium carbonate. Chemical resistance studies reveal maximum weight gain/loss with increasing clay content. Mechanical studies show maximum characteristics for the composites-clay filled 5 % (w/w).

ZHANG Yihe,FU Shaoyun,HUANG Chuanjun,LI Laifeng,LI Guangtao,YAN Qing Technical Institute of Physics,Chemjstry,The Chinese Acadamy of Science,Beijing Graduate School of the Chinese Acadamy of Science,Beijing,
,付绍云,黄传军,李来风,李广涛,严 庆

金属学报 , 2004,
Abstract: Thermosetting polymer based nanocomposites with excellent mechanical and ther mal properties have attracted much attention in recent years. In this paper, preparation methods of this kind of nanocomposites have been briefly introduced. Advances in nanocomposites based on thermosetting polymers including epoxy resin, phenolic resin, unsaturated polyester resin, polynaph thoxazine resin and thermosetting polyimide resin have been systematically summarized. Conclusions that can be drawn from the literatures are presented with discussions of areas in which future research is required.
Environmental Stress Cracking Resistance of Halloysite Nanoclay-Polyester Nanocomposites  [PDF]
Mohd Shahneel Saharudin, Jiacheng Wei, Islam Shyha, Fawad Inam
World Journal of Engineering and Technology (WJET) , 2017, DOI: 10.4236/wjet.2017.53033
Abstract: The environmental stress cracking resistance of halloysite nanoclay-polyester nanocomposites was investigated using fracture mechanics approach. The incorporation of halloysite nanoclay was found to improve the environmental stress cracking resistance of the nano-composites. The storage modulus of nano-composites measured by dynamic mechanical analysis increased remarkably as a function of halloysite nanoclay content. At 0.7 wt% nanoclay, the Tg improved from 72°C to 76°C. The fracture toughness increased up to 33% and time to failure improved 155% with the addition of 0.7 wt% of halloysite nanoclay. The maximum microhardness was found 119% higher for the same nano-filler concentration compared to monolithic polyester. The reinforcement with 1 wt% showed lower fracture toughness due to agglomerations of nanoclay which act as flaws. The presence of agglomerates weakened the bond between nano-particles and matrix hence reduces the environmental stress cracking resistance by halloysite nanoclay reinforcement.
Analysis and Modeling of Curing Polyester Resin in Cylindrical Moulds Heated by Air  [PDF]
Mare?i?, M.,Kosar, V.,Gomzi, Z.
Kemija u Industriji , 2009,
Abstract: The mathematical model of the cure of unsaturated polyester resin in cylindrical mould heated with warm air was suggested and derived. The model assumes convective heat transfer through air on the wall of the mould and conductive heat transfer through the resin. The temperature within the sample changes during the cure process, which is the result of the reaction being exothermal and the process of heat transfer. The addition of the filler changes the thermal properties of the mixture and reduces the amount of heat generated during the reaction in the sample of the same volume, which leads to lower temperature maximums in the center of the cylindrical mould. The model was tested with multiple experiments in which the temperature of the resin inside the mould during the cure process was measured. The heat transfer coefficients between the air and wall of the mould with different speeds of air flow were estimated using independent experiments where the glycerol was used instead of resin. Estimated values were compared with known correlations and good agreement was obtained. Using the suggested model, the cure process in the cylindrical mould can be simulated accurately and influents of the heat transfer and reaction rate on the temperature maximums can be studied.
Exfoliated sodium-montmorillonite in nitrile butadiene rubber nanocomposites with good properties
QingGuo Wang,XiaoHong Zhang,JinLiang Qiao
Chinese Science Bulletin , 2009, DOI: 10.1007/s11434-008-0574-0
Abstract: We prepared and utilized a novel ultrafine fully-vulcanized powder nitrile butadiene rubber (UFPNBR)/sodium montmorillonite (Na-MMT) nanocompound powder, in which nanoscale UFPNBR particles and nanoscale platelets of Na-MMT were isolated and stuck each other. When the UFPNBR/Na-MMT nanocompoud powder was mixed with crude nitrile butadiene rubber (NBR), UFPNBR particles could be easily dispersed in NBR matrix because of good compatibility, and nanoscale Na-MMT was also dispersed well in NBR matrix due to the carrier aidance of UFPNBR particle, thus the NBR/UFPNBR/Na-MMT ternary nanocomposites adapting to industry was fabricated. X-ray diffraction test and scanning electron microscopy (SEM) observation indicated that nanoscale Na-MMT was dispersed well in NBR matrix. Compared with NBR/Na-MMT binary composites, NBR/UFPNBR/Na-MMT ternary nanocomposites have shorter vulcanization time and higher flame retardancy due to the exfoliated Na-MMT in NBR matrix.
P. Prabhu,P. Jawahar,T.P. Mohan
International Journal of Engineering Science and Technology , 2011,
Abstract: Glass fiber reinforced polyester composite (GRP) and hybrid Clay-glass fiber reinforced composites (CGRP) are prepared by vacuum assisted resin infusion technique. The impact properties and barrier resistance nature of these nanocomposites are studied. Hybrid nanocomposites were prepared with glass fibre content of 50 wt.%.Nanoclay is added in different weight fraction of 0, 1, 2, 3, 4 & 5 wt.%. Hybrid clay-glass fiber reinforced polyester composite possess better impact and barrier properties. Hybrid nanocomposites are exposed to various environments like Water, Acid (1% HNO3) and Alkali (1% NaOH) for 30 days. The absorption resistance of nanocomposites is studied. The samples kept in these corrosive environments are subjected to impact testing. The ability of nanocomposites to retain its flexural and impact properties under corrosive environment is better than conventional glass fiber reinforced polyester composite.
Influence of window type on air tightness performance

- , 2017, DOI: 10.11835/j.issn.1674-4764.2017.06.019
Abstract: 采用压差法测量了天津大学校园内5种典型的常用建筑外窗的气密性,这5种窗户分别是PVC单层窗、PVC双层窗、铝合金平开窗、铝合金推拉窗以及铝合金上悬上悬窗,每类窗户测量3组,测量压差控制在0~60 Pa之间。通过测量结果分析了窗框材料、开关窗形式、使用时间以及窗户所处环境对窗户气密性的影响。最终,当压差为5 Pa时,前4种窗户的漏风量分布在10~20 m3/h之间,而铝合金上悬上悬窗的漏风量则在35~40 m3/h之间,漏风量比较大。窗户的渗漏系数C与窗户气密性存在较大关系,压力指数n基本分布与0.5~0.6之间,受气密性影响小。再根据标准GB/T 7106-2008计算了所测外窗的气密性,通过计算,PVC双层窗的气密性最好,平均为5.17 m3/h·m2;铝合金上悬上悬窗的气密性最差,平均为17.9 m3/h·m2。通过对实验的可重复性进行测量,发现经过测量得出低压段(≤ 10 Pa)的漏风量受环境影响较大,高压段(≥ 15 Pa)较小;每两次重复性测试的时间间隔为1周,每两组重复测量之间的误差都小于15%,实验可重复。
The air tightness of 5 different types of common used windows in Tianjin University were measured by blower window method; the measured windows including PVC single, PVC double, aluminum alloy casement, aluminum alloy sash and aluminum alloy slanting sash windows. We totally measured 15 windows with every type 3 windows. The pressure difference between window and outdoor air was controlled in 0~60 Pa during every test. According to the measured results, we compared the influence of window frame material, opening form, function time and outdoor environment on the performance of air tightness. With 5 Pa pressure differences, the infiltration rate of aluminum alloy slanting sash windows was 35~40 m3/h, others were 10~20 m3/h. The window air tightness had a great effect on window leakage coefficient C but less effect on pressure coefficient n, and the coefficient n of all the 15 windows was 0.5-0.6. The air tightness of the 15 windows was calculated through GB/T 7106-2008, the PVC double windows were the tightest with an infiltration rate of 5.17 m3/h·m2, while the aluminum alloy slanting sash windows were worst and its infiltration rate was 17.9m3/h·m2. Based on the results of 3 repeatability tests, we found the outdoor climate influence was negligible on the test results when the pressure difference was larger than 15 Pa. The time interval was one week for every repeatability test, most of the test error was less than 15% between every two tests.
Structure/Property Relationships of Poly(L-lactic Acid)/Mesoporous Silica Nanocomposites  [PDF]
Javier Gudi?o-Rivera,Francisco J. Medellín-Rodríguez,Carlos ávila-Orta,Alma G. Palestino-Escobedo,Saúl Sánchez-Valdés
Journal of Polymers , 2013, DOI: 10.1155/2013/162603
Abstract: Biodegradable poly(L-lactic acid) (PLLA)/mesoporous silica nanocomposites were prepared by grafting L-lactic acid oligomer onto silanol groups at the surface of mesoporous silica (SBA-15). The infrared results showed that the lactic acid oligomer was grafted onto the mesoporous silica. Surface characterization of mesoporous silica proved that the grafted oligomer blocked the entry of nitrogen into the mesopores. Thermal analysis measurements showed evidence that, once mixed with PLLA, SBA-15 not only nucleated the PLLA but also increased the total amount of crystallinity. Neat PLLA and its nanocomposites crystallized in the same crystal habit and, as expected, PLLA had a defined periodicity compared with the nanocomposites. This was because the grafted macromolecules on silica tended to cover the lamellar crystalline order. The g-SBA-15 nanoparticles improved the tensile moduli, increasing also the tensile strength of the resultant nanocomposites. Overall, the silica concentration tended to form a brittle material. 1. Introduction Poly(L-lactic acid) (PLLA) is a linear aliphatic polyester widely used in biomedical applications because it is biodegradable, biocompatible, and nontoxic for the human body. It is also approved by the Food and Drug Administration (FDA) for applications in orthopedic devices [1]. Moreover, PLLA is used as scaffold for bone tissue regeneration [2–6]. However, its slow crystallization, slow degradation rates, low stability during degradation, and relatively poor mechanical properties have limited the applications of this polymer, in particular as a scaffold material [7]. Therefore, new applications for this polymer have proposed the preparation of nanocomposites with inorganic reinforcements as a convenient alternative [8, 9]. Some examples are PLLA nanocomposites with nanoclays [10, 11], nanohydroxyapatite [12, 13], carbon nanotubes [14, 15], and silicon dioxide [16, 17]. In general terms, the mechanical and thermal properties of the resultant nanocomposites have been improved, and the degree of crystallization, and hydrolytic degradation resistance has also been enhanced [14]. However, certain inorganic materials, such as carbon nanotubes [18], are considered to be toxic or harmful to cells. A new class of polymeric materials, for which there are few published studies, takes advantage of mesoporous silicas. These are synthetic materials with ordered arrangements of channels and cavities of different geometries and siloxane walls. One example is SBA-15, a mesoporous material synthetized using triblock copolymer surfactant as a
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.