The influence of UV irradiation on the properties of chitosan films containing keratin

The mechanical, thermal and surface properties of chitosan and chitosan containing keratin hydrolysates have been studied and the influence of UV irradiation on these properties has been compared. The surface properties of chitosan films containing 5%, 15% and 30% of keratin hydrolysate before and after UV irradiation (λ = 254 nm) were investigated by means of contact angle measurements allowing the calculation of surface free energy. The chemical and structural changes during UV irradiation were studied by UV-vis and FTIR-ATR spectroscopy.The changes in mechanical properties such as breaking strength, percentage elongation and Young’s modulus have been investigated. The results have shown that the mechanical properties of the chitosan/keratin films were greatly affected by UV irradiation, but the level of the changes of these properties was smaller in the blend than in pure chitosan and strongly dependent on the time of irradiation and composition of the samples. The contact angle and the surface free energy were altered by UV irradiation, which indicates photooxidation and an increase of polarity of specimens. The range of these changes point to greater susceptibility of chitosan to photooxidation in the presence of keratin.     

The effect of the addition of talc on tribological properties of aramid fiber‐reinforced polyimide composites under high vacuum,ultraviolet or atomic oxygen environment

The aramid fibers‐reinforced polyimide composites filled with talc were fabricated by means of a hot press molding technique, and mechanical and tribological behaviors were comparatively investigated. Experimental results showed that the elastic modulus of the composites increased with an increase of the talc, but the impact intensity and loss factor decreased. Besides, the coefficient of friction decreased with the increase of the talc content. To contrast the effects of the ultrahigh vacuum (VC), ultraviolet (UV) or atomic oxygen (AO) on the composites, experiments without irradiation or after UV or AO irradiation were conducted. Scanning electron microscopy and X‐ray photoelectron spectroscopy (XPS) analysis showed that UV or AO irradiation can change the surface structure and chemical composition of the polymer because of the photooxidation and chemical erosion. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermal and mechanical properties of UV irradiated collagen/chitosan thin films

The thermal and mechanical properties of collagen/chitosan blends before and after UV irradiation have been investigated using thermal analysis and mechanical (Instron) techniques. Comparisons were made with the thermal and mechanical properties of both collagen and chitosan films. Air-dried collagen, chitosan and collagen/chitosan films were exposed to UV irradiation (wavelength 254 nm) for different time intervals. Thermal properties of collagen/chitosan blends depend on the composition of the blend and are not significantly altered by UV irradiation.Mechanical properties such as ultimate tensile strength and ultimate percentage of elongation were much better for collagen films than for collagen/chitosan films. The results have shown that the mechanical properties of the blends were greatly affected by the duration of UV irradiation. Ultimate tensile strength and ultimate percentage elongation decreased after UV irradiation of the blend. Increasing UV irradiation leads to an increase in Young's modulus of the collagen/chitosan blend.     

Study of PDMS conformation in PDMS-based hybrid materials prepared by gamma irradiation

Polydimethylsiloxane-silicate based hybrid materials have recognized properties (high flexibility, low elastic modulus or high mechanical strength) for which there are a large number of applications in development, such as for the bioapplications field. The hybrids addressed in the present study were prepared by gamma irradiation of a mixture of polydimethylsiloxane (PDMS) with tetraethylorthosilicate (TEOS) and zirconium propoxide (PrZr) without addition of any solvent or other product. The materials are homogeneous, transparent, monolithic and flexible. The structure dependence on the PrZr content is addressed. A combination of X-ray diffraction (XRD) and Infrared Spectroscopy (IR) was used. The results reveal that the polymer in the hybrids prepared with PrZr, in a content≤5 wt%, shows a structure similar to that in the irradiated pure polymer sample. In these samples the presence of ordered polymer regions is clearly found. For samples prepared with higher content of Zr almost no ordered polymer regions are observed. The addition of PrZr plays an important role on polymer conformation in these hybrid materials.     

Uniaxial tensile tests and dynamic mechanical analysis of satin weave reinforced epoxy shape memory polymer composite

The utilization of epoxy shape memory polymer composite (SMPCs) as engineering materials for deployable structures has attracted considerable attention in recent decades due to high strength and satisfactory stiffness in comparison with shape memory polymers (SMPs). Knowledge of static and dynamic mechanical properties is essential for analyzing structural behavior and recovery properties, especially for new epoxy SMPCs. In this paper, a new weave reinforced epoxy shape memory polymer composite was prepared with satin weave technique and resin transfer molding technique. Uniaxial tensile tests and dynamic mechanical analysis were carried out to obtain basic mechanical properties and glass transition temperatures, respectively.The tensile strength and breaking elongation of warp specimens were comparable with those of weft specimens. The increment of elastic modulus and hysteresis loop areas became smaller with loading cycles, meaning that cyclic tests could obtain approximate stable mechanical properties. For dynamic mechanical properties, glass transition temperature (T_g) obtained from storage modulus curves was lower than that determined from tan delta curves and T_gs in the warp and weft directions were similar (29.4 °C vs 29.7 °C). Moreover, the storage modulus in response to T_g was two orders of magnitude less than that with respect to low temperature, which demonstrated the easy processibility of epoxy SMPCs near glass transition temperature. In general, this study could provide useful observations and basic mechanical properties of new epoxy SMPCs.     

Nanoindentation of polymers: an overview

In this paper, the application of instrumented indentation devices to the measurement of the elastic modulus of polymeric materials is reviewed. This review includes a summary of traditional analyses of load‐penetration data and a discussion of associated uncertainties. Also, the use of scanning probe microscopes to measure the nanoscale mechanical response of polymers is discussed, particularly with regard to the associated limitations. The application of these methods to polymers often leads to measurements of elastic modulus that are somewhat high relative to bulk measurements with potentially artificial trends in modulus as a function of penetration depth. Also, power law fits to indentation unloading curves are often a poor representation of the actual data, and the power law exponents tend to fall outside the theoretical range. These problems are likely caused by viscoelasticity, the effects of which have only been studied recently. Advancement of nanoindentation testing toward quantitative characterization of polymer properties will require material‐independent calibration procedures, polymer reference materials, advances in instrumentation, and new testing and analysis procedures that account for viscoelastic and viscoplastic polymer behavior.     

A study on the dispersion, preparation, characterization and photo-degradation of polypropylene traced with rare earth oxides

This research work deals with the effect of rare earth oxides on the PP matrix with respect to the thermal and mechanical properties and to the photo-degradation under UV irradiation exposure. The rare earth oxides are used as tracers for the identification of polymer materials, in order to have an economically efficient recycling and high speed automatic sorting of plastic wastes. The addition of 0.1 wt% of such particles of a micrometric size has a minor effect on the mechanical and thermal properties of the traced materials, as well as on the photo-degradation of the polymer after UV irradiation exposure. For 1 wt% tracer content, before UV irradiation treatment, the melting and crystallization temperatures as well as the thermal stability of the PP matrix are slightly increased, whereas the elongation at break decreases from 10 to 50% for a cross-head speed of 250 mm/min. However, the addition of 1 wt% of CeO₂ improves the photo-degradation resistance of the PP matrix to UV exposure due to the UV light screening effects offered by these particles. The SEM images together with the results obtained from image processing show a homogenous dispersion of tracers in the PP matrix.     

Modification of films of heat-resistant polyimides by adding hydrosilicate and carbon nanoparticles of various geometries

The possibility of modifying the properties of poly(4,4′-oxydiphenylene)pyromellitimide films by introducing into prepolymer solutions nanoparticles of various compositions and structures [hydrosilicate nanoparticles in the form of layered structures (montmorillonite) and nanotubes; carbon nanofibers] was examined. New intercalating agents, tetranuclear aromatic diamines, were suggested for pretreatment of montmorillonite prior to introduction into heat-resistant polymers. The mechanical characteristics of the nanocomposites with hydrosilicate nanotubes can be optimized by chemical pretreatment of the nanotubes prior to introduction into the polymer matrix. Introduction of the above-named nanoparticles into the polymer matrix appreciably increases the elastic modulus of the material. The largest increase in the elastic modulus is observed with hydrosilicate nanotubes of the chrysotile structure, coated with an aromatic modifier.     

分子动力学模拟浓度和温度对TATB/PCTFE PBX力学性能的影响

为探讨高聚物粘结炸药(Polymer Bonded Explosive, PBX)的力学性能随温度和高聚物浓度而变化的规律, 用分子动力学(MD)方法和compass力场, 对著名高能炸药1,3,5-三氨基-2,4,6-三硝基苯(TATB)与常用高聚物粘结剂聚三氟氯乙烯(PCTFE)所构成的TATB/PCTFE PBX进行模拟计算. 结果表明, 在一定范围内, 随高聚物浓度的增加, PBX的弹性系数和模量减小, 表明其刚性减小、弹性增加; 而随温度的升高, PBX的刚性减小、弹性增强. 还发现PBX的结合能随浓度增高而增大, 随温度升高而减小.     

Electrospun poly(3‐hexylthiophene)/poly(ethylene oxide)/graphene oxide composite nanofibers: effects of graphene oxide reduction

In this article, we report on the production by electrospinning of P3HT/PEO, P3HT/PEO/GO, and P3HT/PEO/rGO nanofibers in which the filler is homogeneously dispersed and parallel oriented along the fibers axis. The effect of nanofillers' presence inside nanofibers and GO reduction was studied, in order to reveal the influence of the new hierarchical structure on the electrical conductivity and mechanical properties. An in‐depth characterization of the purity and regioregularity of the starting P3HT as well as the morphology and chemical structure of GO and rGO was carried out. The morphology of the electrospun nanofibers was examined by both scanning and transmission electron microscopy. The fibrous nanocomposites are also characterized by differential scanning calorimetry to investigate their chemical structure and polymer chains arrangements. Finally, the electrical conductivity of the electrospun fibers and the elastic modulus of the single fibers are evaluated using a four‐point probe method and atomic force microscopy nanoindentation, respectively. The electrospun materials crystallinity as well as the elastic modulus increase with the addition of the nanofillers while the electrical conductivity is positively influenced by the GO reduction. Copyright © 2016 John Wiley & Sons, Ltd.     

半结晶硬弹性聚合物的研究进展

硬弹性材料是结晶或非结晶聚合物在特定的条件下加工而形成的,这类材料表现出高弹性、高模量和突出的低温弹性。文章综述了半结晶硬弹性聚合物的力学性能、形态、结构、弹性机理、制备和应用等。     

New semi-interpenetrating network hydrogels: synthesis, characterization and properties

Amphiphilic hydrogels composed of aliphatic polyesters and poly(ethylene glycol) have potential applications in drug delivery, tissue engineering and other biomedical devices due to their advantageous biological properties, biocompatibility and biodegradability. However, they also exhibit some shortcomings in terms of their reactivity, swelling and mechanical properties. To address these limitations, new semi-interpenetrating network (semi-IPN) hydrogels based on poly(ethylene glycol)-co-poly(epsilon-caprolactone) (PEG-PCL) diacrylate macromer and hydroxypropyl guar gum (HPGG) were prepared by a low intensity ultraviolet (UV) light irradiation method, and characterized by FT-IR, DSC and WAXD analysis. Their properties were evaluated by investigating the swelling kinetics, dynamic mechanical rheology and the release behavior for bovine serum albumin (BSA). It was found that the introduction of the semi-IPN structure and HPGG decreased the crystallinity of PEG segments in the hydrogel, and improved the swelling and mechanical properties of the hydrogel, as well as lowered the release percentage of BSA from the hydrogel. Such hydrogel materials may have more advantages as a potentially interesting platform for the design of medical devices.The elastic modulus (G') and viscous modulus (G') as a function of frequency for various hydrogel samples.     

Synthesis of TiO(2)-PMMA nanocomposite: using methacrylic acid as a coupling agent

Inorganic-polymer nanocomposites are of significant interest for emerging materials due to their improved properties and unique combination of properties. Methacrylic acid (MA), a functionalization agent that can chemically link TiO2 nanomaterials (n-TiO2) and polymer matrix, was used to modify the surface of n-TiO2 using a Ti-carboxylic coordination bond. Then, the double bond in MA was copolymerized with methyl methacrylate (MMA) to form a n-TiO2-PMMA nanocomposite. The resulting n-TiO2-PMMA nanocomposite materials were characterized by using thermal analysis, electron microscopy, and elemental analysis. The dynamic mechanical properties (Young's and shear modulus) were measured using an ultrasonic pulse technique. The electron microscopy results showed a good distribution of the nanofillers in the polymer matrix. The glass transition temperature, thermal degradation temperature, and dynamic elastic moduli of the nanocomposites were shown to increase with an increase in the weight percentage of nanofibers in the composite. The resulting nanocomposites exhibited improved elastic properties and have potential application in dental composites and bone cements.     

通过掺杂柔性二胺单体增强聚酰亚胺性能:分子动力学模拟

聚酰亚胺(PI)被视为一类以其卓越性能而闻名的高性能聚合物材料。传统聚酰亚胺的一个关键问题是其熔体的加工性能较差。在本研究中,设计了一种新的聚酰亚胺单体Am-Di,其特点是由氮原子连接的苯环组成的柔性结构。通过详尽的研究,我们对Am-Di掺杂到聚酰亚胺中对其玻璃化转变温度、均方位移、力学性能和相对介电常数等性质的影响进行了深入探讨。结果表明,在聚酰亚胺体系中,掺杂新型二胺可以加速聚酰亚胺分子链的运动,从而降低聚酰亚胺体系的玻璃化转变温度。在Am-Di掺杂量为20%的情况下,PI-20%表现出最高的弹性模量(4.505Gpa),比纯PI高1.2倍。此外,随着掺杂比例的增加,聚酰亚胺的相对介电常数降低。这些发现表明,Am-Di的掺杂对聚酰亚胺材料的性能具有积极影响,特别是在增强机械性能和调控电气性能方面,为进一步改进聚酰亚胺材料的设计和应用提供了有价值的见解。     

AFM nanoindentation to determine Young’s modulus for different EPDM elastomers

AFM nanoindentation was investigated as a method for determining the micromechanical properties of polymer materials. It is generally accepted that the shape of the tip of the cantilever undergoes a change in a standard AFM setup. The shape defines the projected contact area, so it is a parameter directly proportional to the elastic modulus; any change in the shape thus affects the accuracy of the results. The method suggested in this paper relies on the introduction of an experimentally determined tip-area function. Values for Young’s modulus were calculated for EPDM samples with different degrees of cure and crystallinity. The degree of crystallinity has a greater impact on the mechanical properties of the material than the degree of cure. Depending on the amplitude of the indentation, the E-moduli determined by AFM are systematically higher. When studying different regions of polymer materials, the values of the E-modulus determined by AFM become identical to those measured by means of DMA on extrapolation of the modulus at zero indentation.     

Electrospun polymer nanofibers: Mechanical and thermodynamic perspectives

This article reviews and discusses some open problems concerning polymer materials of reduced sizes and dimensions. Such objects exhibit exceptional physical properties when compared with their macroscopic counterparts. More specifically, abrupt increases in polymer nanofiber elastic modulus have been observed when diameters drop below a certain value. In addition, temperature dependence of elastic modulus is highly influenced by fiber diameter. Mechanical (macroscopic) analyses have failed to provide satisfactory explanations for the mechanisms ruling such features, calling for detailed microscopic examination of the systems in question. A hypothesis bridging the current knowledge gaps is presented. The key element of this hypothesis is based on confinement of the supermolecular microstructure of polymer nanofibers and its dominant role in the deformation process. This suggestion challenges the commonly held view suggesting that surface effects are the most significant parameters impacting mechanical and thermodynamic nanofiber behaviors. The review will focus on the mechanical and thermodynamic properties of electrospun polymer nanofibers, selected as representatives of nanoscale polymer objects. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Relationship between the polymer/silica interaction and properties of silica composite materials

Cast film composites have been prepared from aqueous polymer solutions containing nanometric silica particles. The polymers were polyvinyl alcohol (PVA), hydroxypropylmethylcellulose (HPMC) and a blend of PVA‐HPMC polymers. In the aqueous dispersions, the polymer–silica interactions were studied through adsorption isotherms. These experiments indicated that HPMC has a high affinity for silica surfaces, and can adsorb at high coverage; conversely, low affinity and low coverage were found in the case of PVA. In the films, the organization of silica particles was investigated through transmission electron microscopy (TEM) and small‐angle neutron scattering (SANS). Both methods showed that the silica particles were well‐dispersed in the HPMC films and aggregated in the PVA films. The mechanical properties of the composite films were evaluated using tensile strength measurements. Both polymers were solid materials, with a high‐elastic modulus (65 MPa for HPMC and 291 for PVA) and a low‐maximum elongation at break (0.15 mm for HPMC and 4.12 mm for PVA). In HPMC films, the presence of silica particles led to an increase in the modulus and a decrease in the stress at break. In PVA films, the modulus decreased but the stress at break increased upon adding silica. Accordingly, the polymer/silica interaction can be used to tune the mechanical properties of such composite films. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1134–1146, 2006     

Aging effect on the mechanical properties of hybrid gels

Sol-gel derived unsupported films and thin rods have been obtained from co-hydrolysis of triethoxysilane and methyldiethoxysilane. The materials are flexible, dense and transparent. Films and rods have been aged for different periods of time in air at room temperature. The elastic modulus has been measured by means of tensile or flexural tests. Measurements showed an increase of elastic modulus with aging time and showed different values for films and rods. The observed evolution of mechanical properties has been related to a corresponding structural modification as highlighted mainly by MAS-NMR studies. Analyses pointed out the crucial role of condensation processes and showed that the stiffness increase arises from the formation of relatively few bonds which link and constrain pre-existing mobile network regions.     

Effect of ultraviolet radiation on polyethylene naphthalate films irradiated with high-energy heavy ions

The effect of UV radiation in the spectral range of 280–400 nm on polyethylene naphthalate (PEN) films has been studied. Changes in the optical absorption spectra of PEN after exposure to accelerated ions and UV radiation have been revealed. Changes in the surface properties have been explored, and the depth of the degraded polymer layer after long-term UV irradiation in air has been measured. Depending on the treatment time, the depth has made 0.1–0.9 μm. The photoablation rate and the quantum yield of monomer unit removal due to UV irradiation of the PEN films have been estimated at ~0.7 × 10^?4 molecule/photon. The possibility of the formation of asymmetric pores in PEN films using controlled photooxidative degradation has been shown.     

Relaxation properties of gradient polymer materials based on network poly(urethane-isocyanurates) produced via a modified method

The relaxation properties of gradient polymer materials produced via a modified method are studied through dynamic mechanical analysis and through measurement and approximation of stress-relaxation curves in a wide temperature range under static conditions. The physicomechanical properties of polymer materials produced via the new method are substantially improved, and the range of properties is markedly widened. The investigated materials can possess any values of the elastic modulus, including those inherent in the region of transition from the glassy state to the rubbery state; moreover, they demonstrate a quasi-elastic behavior characteristic of glasses and rubbers.