Shape memory properties of electrospun nafion nanofibers

Nanoscaled non-woven fibers with shape memory effect are successfully fabricated via electrospinning method from Nafion solutions consisting of a little poly(ethylene oxide) (PEO). Scanning electron microscopy (SEM) investigation shows the electrospun nanofibers with average diameters in the range 170–410 nm. The electrospun nanofibers exhibit excellent shape memory properties. When deformed Nafion nanofibers are stimulated upon heat, the temporary shape responds rapidly, and then recovers to the permanent shape in less than one minute. The shape recovery ratios and shape fixity ratios of Nafion nanofibers with 0.3 wt%, 0.5 wt% and 0.7 wt% PEO are all above 90 %. In shape memory cycle, fibrous structure is stable after the stretching recovery. Shape memory Nafion nanofibers have various potential applications in smart structures and materials in the future.     

Polyurethane smart fiber with shape memory function: Experimental characterization and constitutive modelling

Segmented polyurethane (PU) polymers are known to have shape memory function, i.e., when they reach certain temperatures, they deform into the memorized shape from any temporary one. In the present study, PU polymers were spun into fibers using the conventional extrusion process to investigate the feasibility of producing smart fibers with shape memory function. The shape memory polymers (SMPs) and their spun fibers were characterized using DSC, DMTA, and tensile test. In particular, the thermo-mechanical deformation behavior, which enables to evaluate the shape memory performance of the SMPs, was characterized using DMTA. Then, the linear viscoelastic theory was utilized for mathematical modelling of the thermo-mechanical behavior of the SMPs. For the shape memory fibers, the large deformation characteristics were also investigated using the thermo-mechanical test, necessitating the development of nonlinear viscoelastic theory to formulate a constitutive equation and to provide an effective tool for designing smart textile structure.     

Thermomechanical and Shape Memory Performances of Thermo-sensitive Polyurethane Fibers

This study is the first step to investigate usability of shape memory polyurethane (SMPU) fibers for smart garment applications. SMPU fibers were spun by wet spinning process and chemical/mechanical characterization was carried out. SMPU solutions were prepared with two different concentrations (20 % and 25 %) and three different coagulation bath concentrations (0 %, 1 % and 3 %) were used for determining optimum spinning parameters. For investigating influences of spinning process on crystal structure, mechanical, thermal and shape memory performances of fibers, X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM) and mechanical tests were conducted. DSC and DMA analysis results show that shape memory polyurethane fibers have a glass transition temperature about 35-40 oC which is suitable for body temperature. Moreover, SMPU fibers showed good tensile performance with an average tenacity of 1.38 cN/dtex and elongation at break of 350 %. Thermo mechanical test results showed that, all shape memory fibers have good shape memory effect with recovery and fixity ratios up to 91 % and 71 % respectively.     

An evaluation of the three-dimensional geometric shape of moulded bra cups

Bra cup moulding is currently a remarkable process in the production of seamless intimate apparel. The process is highly complex, time-consuming and error-prone due to the large variations of foam and lamination properties, cup styles and sizes, and geometric features of graduated padding. In particular, the three-dimensional (3D) geometric shape of foam cups is difficult to assess accurately because they are very soft and readily deform. In cases that involve fitting problems, shape modifications of the mould head and determination of the optimal moulding conditions have undergone repeated trials and errors. There is limited knowledge about the effects of foam properties and cup parameters in the controlling of moulding conditions. This study adopts a parameterization-based remesh algorithm method to evaluate the 3D shapes of the convex surface of scanned cup samples. The shape conformity of the cup is quantified in accordance to the corresponding mould head. In this respect, the moulding conditions that would achieve the most desirable geometric shapes of bra cups can be accurately and objectively demonstrated. Based on moulding experiments with 6 types of polyurethane (PU) foam materials, empirical equations that associate the cup shape conformity and the shape deviations from selected cup sectional curves are established. Through the use of non-linear regression models, the shape conformity of the moulded cups can be predicted by moulding conditions with reasonable accuracy. The shape conformity provides effective guidelines for quality assurance and improves production efficiency of bra cup moulding. Moreover, thermal-mechanical properties, such as compressive strain and softening temperature obtained from thermomechanical analysis (TMA) scans, provide a good understanding of cup shape conformity and determine the lowest moulding temperature at initial trails of the bra cup moulding process. Surprisingly, in pliable foams, the cup size does not have an apparent effect on the moulding conditions to achieve optimal cup shape conformity. The results reveal that the moulding conditions for sizes 34B and 34D could remain the same for pliable foam materials. Nevertheless, in the case of more rigid foams, a higher moulding temperature is required to achieve a desirable cup shape for size 34D as more energy is required for the heat-setting of foam materials with higher proportions of hard segments at the moulding of a larger cup size in anticipation of larger deformations.     

Flexible cross-linking of shape memory polyurethane by a long polyethyleneglycol spacer

Flexible linking of shape memory polyurethane (SMPU) was tried with a long polyethyleneglycol (PEG) spacer (PEG-600 or PEG-1000) longer than the one tested before (PEG-200). The SMPU was composed of MDI, polytetramethyleneglycol (PTMG), 1,4-butanediol (BD), glycerol, and PEG as a spacer. PEG connected the glycerol hydroxyl group of polyurethane chain via MDI as a connecting agent. Significant increase in both maximum stress and strain at break was attained simultaneously, because of the flexible structure of PEG. Especially, it was shown in the stress-strain curve that the PEG-linked SMPU showed similar behavior and superior tensile mechanical properties to natural rubber. Shape recovery of the PEG-linked SMPU went up to 96 %, and shape retention remained low compared to linear one. PEG-1000 was better than PEG-600 in enhancing the overall tensile strength and shape memory of SMPU.     

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.     

Structure-property relationship and shape memory effect of polyurethane copolymer cross-linked with pentaerythritol

Polyurethane block copolymers chemically cross-linked by pentaerythritol, a four-way cross-linker, are tested for the shape memory effect. One of the copolymers shows higher shape recovery than any other shape memory copolymer synthesized by us so far. The copolymer maintains a surprising 94 % shape recovery after the third cyclic test. The four-way cross-linking by pentaerythritol and interaction between hard segments are mainly responsible for the very high shape recovery. Tensile mechanical properties also significantly improve by cross-linking. Glass transition temperature (T _g ) slightly increases with cross-linking content. Other characterization such molecular weight, IR, and X-ray diffraction is also carried out to understand the arrangement of copolymer chains.     

Effect of cross-linking agent structure on the shape memory property of polyurethane block copolymer

Effect of cross-linking agent on the shape memory and mechanical property of polyurethane (PU) block copolymer is comprehensively investigated. The selected chemical cross-linking agents are glycerol, 1,2,6-trihydroxyhexane, and 2,4,6-trihydroxybenzaldehyde that are differentiated from each other in having remote hydroxyl group and aromatic ring. Significant increase in maximum stress was observed for all of the cross-linked PUs, although the cross-linker structure was different. Structural change of PU after cross-linking as evidenced by differential scanning calorimetry and infrared spectra was not detected, suggesting that interaction between PU chains remained intact. Shape recovery went to as high as 95 % after cross-linking for all of the cross-linking agents, and shape retention did not improve even if cross-linker was used. The remarkable increase in shape recovery and maximum stress definitely originated from the employment of a cross-linking agent, and the effect of different cross-linker structure on shape memory and mechanical property is discussed.     

Incorporation of surface modified graphene nanoplatelets for development of shape memory PLA nanocomposite

In this study, a temperature sensitive shape memory polymer (SMP) system based on polylactic acid (PLA) has been developed and the effect of graphene nanoplatelets (GNPs) on the shape memory properties was evaluated. Dispersion of GNPs in PLA was improved with the aid of a zwitterionic surfactant. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the surface modified graphene nanoplatelets (SMGNPs) were exfoliated and homogenously dispersed in the PLA matrix due to enhancement of the polymer-graphene interaction. Mechanical properties of the samples namely stiffness and elasticity were increased upon incorporation of graphene nanoplatelets accompanied by their good dispersion in the PLA matrix. Furthermore, differential scanning calorimetry (DSC) revealed that the nucleation effect of graphene promote the crystallization and noticeably enhanced the degree of crystallinity. Finally, prominent mechanical properties along with high degree of crystallization due to fine dispersion of surface modified graphenes, resulted in drastic improvement in shape memory performance.     

Glass transition behavior of corn distillers dried grains with solubles (DDGS)

Distillers dried grains with solubles (DDGS), a major co-product from the corn ethanol industry, has high feed value for its chemical composition. The ratio of wet distillers grains (WDG) and condensed distillers solubles (CDS) added during the production process determines the chemical composition of DDGS. Effect of changing this ratio and the influence of moisture content on glass transition behavior of DDGS was studied. Five prediction models were evaluated to explain the glass transition of DDGS. The mixed trends in the result indicated the complex behavior of DDGS particles and revealed that both moisture content and chemical composition impact the glass transition behavior of DDGS. Onset glass transition temperature ranged from 20 to 30 °C depending on the chemical composition. Kwei equation predictions were better than the predictions by Gordon-Taylor equation. The glass transition temperature of DDGS can be mathematically explained by combining the moisture content and chemical components protein, fiber, glycerol, and sugar percent. The artificial neural network (ANN) model gave a better prediction of onset and midpoint glass transition temperature of DDGS and this might be due to the accurate mapping of the interaction between chemical components.     

Protective Roles of Brassinolide on Rice Seedlings under High Temperature Stress

Two indica rice(Oryza sativa L.)materials,Xieqingzao B(sensitive to heat stress)and 082(tolerant to heat stress),were used to study the role of brassinolide(BR)in protection of rice seedlings from heat stress.Young seedlings were subjected to high temperature(38℃/30℃)and sprayed with 0.005 mg/L of BR.Analysis was conducted on the contents of chlorophyll,protein and malondialdehyde(MDA),the leakage of electrolyte,the activities of peroxidase(POD)and superoxide dismutase(SOD)and their isozymes expression levels in leaves.Under the high temperature treatment,application of BR significantly increased the contents of chlorophyll and protein,and the activities of POD and SOD,and reduced the content of MDA and the leakage of electrolyte in the leaves of the heat-sensitive material Xieqingzao B,whereas BR had less effect on those of the heal-tolerant material 082 relatively.The BR treatment enhanced the expression of POD isozymes in the Ieaves of both materials.Under the high temperature stress and BR treatment.the expression of four SOD isozymes reduced in 082,but the expression of two SOD isozymes increased in Xieqingzao B.This suggests that BR plays an important role in protection of rice seedlings from heat stress by enhancing the activities or expression level of protective enzymes in the leaves.The materials with various heat-tolerance might differ in the mechanism of response to heat stress with BR application.     

The characterization and effects of the alizarin series dyes grafted to polyurethane copolymers on the photoluminescence and low temperature flexibility

Alizarin-series dyes (alizarin, alizarin red S, alizarin yellow GG, or mordant orange) are grafted onto shape memory polyurethane (PU) through an allophanate bonding, and the photoluminescence and the low-temperature flexibility of the resulting PUs are tested. The PU is mainly composed of 4,4′-methylenebis(phenylisocyanate) (MDI), poly (tetramethyleneglycol) (PTMG), and 1,4-butanediol (BD), and the dye is connected, through another MDI, to the carbamate moiety of the PU chain. The PUs with different dye contents are characterized, and their shape recovery and photoluminescence properties are compared. With respect to the tensile mechanical properties, the maximum stress increases up to 50 MPa, and the strain remains above 1000 % even after the dye is grafted onto the PU. The shape recovery is as high as 99 %, and the shape retention improves as the dye content increases. Finally, the photoluminescence of the PUs is demonstrated by the luminescent light emission test, and the dye-grafted PU shows excellent low-temperature flexibility compared with that of linear PU.     

Influence of Drawing and Annealing on the Crystallization,Viscoelasticity, and Mechanical Properties for Middle-molecular-weight Polyethylene Fishing Monofilaments

The influence of drawing and annealing on the crystallization, viscoelasticity and mechanical properties for middle-molecular-weight polyethylene (MMWPE) fishing monofilaments was investigated. It was found that the drawing procedure had a positive effect on the crystallization of the MMWPE fishing monofilaments. Meanwhile, the glass transition temperature of the MMWPE monofilaments shifted to higher temperature, and the α-relaxation associated with crystalline phases became higher and broader with the increase in the drawing ratio. Moreover, the breaking strength of MMWPE fishing monofilaments can be effectively improved by increasing the drawing ratio. Meanwhile, the knot strength increased first and then decreased. However, the increase in annealing temperature improved the knot strength. With increasing annealing temperature, the orientation factor decreased and induced the γ-relaxation peak at high magnitude. This indicated that the amorphous structure could become disordered during annealing treatment. In addition, the annealing temperature can clearly influence the working temperature dependence of the stress-strain behavior. When the working temperature rose from 20 °C to 30 °C, the MMWPE monofilaments after annealing at 120 °C exhibited low modulus loss due to their high α- transition temperature. Thus, an important method for improving the mechanical properties by controlling the drawing and annealing conditions was established.     

The grafting of recycled polyol from waste polyurethane foam onto new polyurethane and its impact on shape recovery and water vapor permeation

Recycled polyols from waste polyurethane (PU) foams were grafted onto PU to improve the properties such as tensile strength, shape recovery, low-temperature flexibility, and water compatibility. The recycled polyol was either purified by column chromatography before grafting or was used directly for grafting. The soft segment melting temperature of PU did not notably increase with the addition of polyol, whereas the glass transition temperature increased with increased polyol content. The tensile strength sharply increased at low polyol content and decreased at high polyol content, while the strain at break did not significantly change with an increase in polyol content. The shape recovery at 10 oC notably improved compared with unmodified PU and remained high after four cyclic tests. Polyol-grafted PU demonstrated better lowtemperature flexibility and reduced the water vapor permeability of PU membranes. Overall, grafting recycled polyol onto PU significantly improved the tensile stress, shape recovery, and low-temperature flexibility of PU.     

Synchrotron SAXS study on the micro-phase separation kinetics of segmented block copolymer

The phase transition behavior and isothermal micro-phase separation kinetics of polyester-based thermoplastic elastomer were studied using the synchrotron X-ray scattering (SAXS) method. The structural changes occurring during heating period were investigated by determining the changes of the one-dimensional correlation function, interfacial thickness and Porod constant. Based on the abrupt increases of the domain spacing and interfacial thickness, a major structural change occurring well below the melting transition temperature is suggested. Those changes are explained in terms of melting of the thermodynamically unstable hard domains or/and the interdiffusion of the hard and soft segments in the interfacial regions. SAXS profile changes during the micro-phase separation process were also clearly observed at various temperatures and the separation rate was found to be sensitively affected by the temperature. The peak position of maximum scattering intensity stayed constant during the entire course of the phase separation process. The scattering data during the isothermal phase separation process was interpreted with the Cahn-Hilliard diffusion equation. The experimental data obtained during the early stage of the phase separation seems to satisfy the Cahn-Hilliard spinodal mechanism. The transition temperature obtained from the extrapolation of the diffusion coefficient to zero value turned out to be about 147±2°C, which is close to the order-disorder transition temperature obtained from the Porod analysis. The transition temperature was also estimated from the invariant growth rate. By extrapolating the invariant growth rate to zero, a transition temperature of about 145±2°C was obtained.     

Effect of glycerol cross-linking and PDI on the shape memory effect and mechanical properties of polyurethane

A series of shape memory polyurethane (PU) copolymers synthesized from 1,4-phenyldiisocyanate (PDI), poly(tetramethyleneglycol) (PTMG), 1,4-butanediol (BD) as a chain extender, and glycerol as a cross-linking agent were tested for the mechanical properties and the shape memory effect at the temperature 20 °C above melting temperature (T _m), and were compared with other PUs synthesized from 4,4′-methylene-bis-phenyldiisocyanate (MDI), PTMG, and BD. Mechanical properties and shape memory effect were improved substantially by adopting both PDI and glycerol. Interestingly, enthalpy of melting and T _m were not affected by the glycerol content. Vibration and shock absorption ability was investigated by measuring both loss tan δ and storage modulus with dynamic mechanical analyzer (DMA).     

Fluorescence characterization of LaRC PETI-5, BMI, and LaRC PETI-5/BMI blends

In the present study, the fluorescence behavior of a phenylethynyl-terminated imide (LaRC PETI-5) resin, a bismaleimide (BMI) resin, and various LaRC PETI-5/BMI blends with different blend compositions has been characterized as a function of heat-treatment temperature, using a steady-state fluorescence technique with a front-face illumination method for solid-state films. It is observed that there are distinguishable changes in the spectral shape, size, and position of fluorescence with varying heat-treatment temperature in the pure and blend samples. The result is qualitatively explained in terms of charge transfer complex formation as well as microenvironmental change with local mobility and viscosity occurring in the LaRC PETI-5, BMI, and their blends during the cure process. The result also implies that a steady-state fluorescence technique may be a useful tool to understand the processing conditions of polyimides and their blends in the film form on the basis of their thermo-photophysical responses.     

Incorporating shape memory properties in poly(ethylene terephthalate) film by isothermal crystallization

In this paper the peculiar shape memory property of semicrystalline PET films is studied. The shape memory samples were prepared through isothermal crystallization of glassy PET films at different temperatures between 120 and 230 °C for 15 and 4 minutes. It was assumed that the incorporated shape memory constitution is due to crystalline and amorphous parts and also third phase i.e. a rigid amorphous fraction (RAF) which rose by increasing the degree of crystallinity. The microstructure of samples was probed by DSC and WAXD analysis, and concluded that isothermal crystallization at temperature which spinodal decomposition mechanism is dominant, brings the formation of secondary crystal lamellas in amorphous regions between pre-existing lamellar stacks, incorporating shape recovery in the samples. As the crystallization proceeds with time or at higher temperatures, the fraction of RAF increases leading to suppression of shape memory effect.     

Glucose cross-linking of polyurethane copolymer and its impact on the elevation of mechanical properties and shape memory effect

Effect of glucose cross-linking on the shape memory and mechanical properties of polyurethane (PU) block copolymer was investigated. Glucose was selected due to its large number of free hydroxyl groups, easy availability, miscibility with other reactants, and cyclic structure. The glycerol cross-linking did not affect the molecular interaction and phase separation of hard and soft segments in polyurethane structure as judged from IR and DSC analysis. Viscosity of glucose cross-linked PU increased after cross-linking due to the cross-linked structure. Maximum stress drastically improved with the adoption of glucose as a cross-linker together with a slight increase in strain at break. Shape recovery also increased with the adoption of glucose as a cross-linker, and shape recovery was not diminished after four cyclic shape recovery tests. In contrast, shape retention significantly decreased if glucose was included for two different hard segment contents. Finally, glucose cross-linking was compared with other cross-linkers used in shape memory polymer and the advantage of glucose cross-linking was discussed.     

Thermomechanical properties and shape memory effect of PET-PEG copolymers cross-linked with pentaerythritol

Poly(ethylene terephthalate) (PET) and poly(ethylene glycol) (PEG) copolymers cross-linked with pentaerythritol, a four-way cross-linker, are prepared to compare their mechanical and shape memory properties with the one cross-linked by glycerol. Composition of PEG and pentaerythritol is varied to search for the one with the best mechanical and shape memory properties. The highest shape recovery rate is observed for the copolymer composed of 30 mol% PEG-200 and 2.5 mol% pentaerythritol. Four-way cross-linking by pentaerythritol significantly improves shape recovery rate and retention of high shape recovery rate after repeated use compared to the one cross-linked by glycerol, a three-way cross-linker, and difference and advantage of additional cross-linking point are discussed.