Sensitive Shape Memory Research Articles

Enhancing Wool Fabric Easy Care Properties by Shape Memory Polyurethane Finishing

Wool fabrics having temperature sensitive shape memory effect were fabricated by using a shape memory polyurethane (SMPU) treatment. The contribution of SMPU treatment on bagging recovery and felting shrinkage, crucial properties for end use performance, was investigated by a test procedure including hot water conditions simulating laundry of garments according to the Woolmark TM31 standard. Chemical and morphological analyses, bending rigidity, and tear strength tests were also carried out to determine the effects of SMPU treatment on performance properties. SMPU treatment significantly increased weight and rigidity of fabrics. Most notably, SMPU treated wool fabric exhibited excellent temperature sensitive bagging recovery stimulated by a washing procedure. Also, anti-felting and weight loss performances were quite high compared to raw and commercial polyurethane-treated fabrics.

Study on the release behaviors of berberine hydrochloride based on sandwich nanostructure and shape memory effect.

Nanofibrous drug delivery systems (DDSs) recently have attracted remarkable interest, especially their potential to program dosage of the encased drug intelligently. Despite this, the exploration of efficient strategy to precisely program drug release from nanofibrous DDS still remains a significant challenge. In this study, we electrospun a near-body temperature (Ttrans≈42°C) sensitive shape memory polyurethane in three stages through sequential electrospinning technology, and prepared a sort of sandwich structural membrane, comprising of top, inner and bottom layers, wherein a natural antibacterial agent, berberine hydrochloride (BCH), was imbedded inside the middle layer. As demonstrated by the results obtained from tensile testing and morphology characterization, the prepared sandwich structural membrane and the nanofibrous membrane with homogenous structure exhibited not only desirable mechanical properties but also surface morphologies. In addition, the release period can be significantly prolonged in virtue of the sandwich structure. As revealed by the experiment of in vitro drug release, it took nearly 144h to release 80wt% BCH from sandwich structural membrane, while as little as 72h was observed to release the same amount of BCH from that with homogenous structure. More interestingly, the encapsulated BCH is capable to be released in a controlled manner owning to the thermo-sensitive shape memory effect, and the release rate of BCH can be accelerated by stretching and fixing the nanofibrous membranes into certain ratios prior to release. Collectively, this study provides a facile strategy to design and prepare a reliable and smart DDS, i.e. sandwich structural membrane, which may enhance the availability of BCH and also intelligently avoid the bacterial infection.

Hybrid Nanocomposites of Cellulose/Carbon-Nanotubes/Polyurethane with Rapidly Water Sensitive Shape Memory Effect and Strain Sensing Performance.

In this work, a fast water-responsive shape memory hybrid polymer based on thermoplastic polyurethane (TPU) was prepared by crosslinking with hydroxyethyl cotton cellulose nanofibers (CNF-C) and multi-walled carbon nanotubes (CNTs). The effect of CNTs content on the electrical conductivity of TPU/CNF-C/CNTs nanocomposite was investigated for the feasibility of being a strain sensor. In order to know its durability, the mechanical and water-responsive shape memory effects were studied comprehensively. The results indicated good mechanical properties and sensing performance for the TPU matrix fully crosslinked with CNF-C and CNTs. The water-induced shape fixity ratio (Rf) and shape recovery ratio (Rr) were 49.65% and 76.64%, respectively, indicating that the deformed composite was able to recover its original shape under a stimulus. The TPU/CNF-C/CNTs samples under their fixed and recovered shapes were tested to investigate their sensing properties, such as periodicity, frequency, and repeatability of the sensor spline under different loadings. Results indicated that the hybrid composite can sense large strains accurately for more than 103 times and water-induced shape recovery can to some extent maintain the sensing accuracy after material fatigue. With such good properties, we envisage that this kind of composite may play a significant role in developing new generations of water-responsive sensors or actuators.

Collagen skin, a water-sensitive shape memory material.

By collagen skin (CS) we mean a material with only collagen fibres in a natural animal skin. Following continuous research of collagen biochemistry, CS shows its superiority in various applications such as leather, wound dressing and absorbing materials. This study discovered the water-induced shape memory effect of CS and exploited the corresponding mechanisms in terms of its molecular and morphological structure. It is revealed that CS can completely fix into a temporary shape and retain a high shape recovery ratio (>90%) under repeatable memory cycles. The reversible cleavage and re-formation of interpeptide hydrogen bonds can work as a "switch" to trigger the shape deformation while peptide chains together with cross-links within collagen work as a "netpoint" for shape recovery. Such water-responsive adaptable mechanical behaviour (a switchable modulus) allows CS to be either used as a robotic handle for loading or as a flexible material for covering. This discovery will provide new opportunities and guidance in emerging research areas such as shape memory devices, biomimetic actuators and artificial skins as well as the physiological function of an animal skin.

Shape Memory Polymer Composites of Poly(styrene-b-butadiene-b-styrene) Copolymer/Liner Low Density Polyethylene/Fe3O4 Nanoparticles for Remote Activation

Magnetically sensitive shape memory poly(styrene-b-butadiene-b-styrene) copolymer (SBS)/liner low density polyethylene (LLDPE) composites filled with various contents of Fe3O4 nanoparticles were prepared. The influence of the Fe3O4 nanoparticles content on the thermal properties, mechanical properties, fracture morphology, magnetic behavior, and shape memory effect of SBS/LLDPE/Fe3O4 composites was systematically studied in this paper. The results indicated that homogeneously dispersed Fe3O4 nanoparticles ensured the uniform heat generation and transfer in the alternating magnetic field, and endowed the SBS/LLDPE/Fe3O4 composites with an excellent magnetically responsive shape memory effect. When the shape memory composites were in the alternating magnetic field (f = 60 kHz, H = 21.21 kA·m−1), the best shape recovery ratio reached 99%, the shape retention ratio reached 99.4%, and the shape recovery speed increased significantly with the increment of Fe3O4 nanoparticles. It is anticipated that tagging products with this novel shape memory composite is helpful for the purpose of an intravascular delivery system in Micro-Electro-Mechanical System (MEMS) devices.

PH- and Thermal-Responsive Multishape Memory Hydrogel.

A multistimuli sensitive shape memory hydrogel with dual and triple shape memory properties was prepared by grafting dansyl groups into the network of polyacrylamide (PAAM). The hydrophobic aggregation of dansyl groups acted as molecular switches, which showed reversible aggregation-disaggregation transition in aqueous solution in response to the pH or temperature change.

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.

Shape Memory Hydrogel based on a Hydrophobically-Modified Polyacrylamide (HMPAM)/α-CD Mixture via a Host-Guest Approach.

A novel thermally sensitive shape memory (SM) hydrogel is prepared by block copoly-merization of a cationic surfactant monomer, dimethylhexadecyl[2-(dimethylamino)ethylmethacrylate]ammoniumbromide (C(16)DMAEMA), and acrylamide (AM) in the presence of α-cyclodextrin (α-CD) using N,N'-methylenebisacrylamide (MBA) as a crosslinker. XRD, solid state (13)C NMR, and DSC measurements show that the crystalline domains, induced by the hydrogen bonds between α-CDs threaded on the hydrophobic units of the polymer chains through the host-guest approach, can reversibly melt and crystallize at different temperatures. Rheological measurements show that both the elastic modulus G' and viscous modulus G'' drastically change due to the formation and dissolution of the crystalline domains. These thermo-sensitive crystalline domains serve as reversible physical crosslinks, endowing the hydrogel with excellent SM properties. Cyclic experiments show that the hydrogel can recover to almost 100% of the deformation in each cycle and can be reused several times.

Multi-stimuli sensitive shape memory poly(vinyl alcohol)-graft-polyurethane

A multi-stimuli sensitive shape memory poly(vinyl alcohol)-graft-polyurethane was synthesized. Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H-NMR) confirmed the chemical structure of the material. The material exhibits good water-induced shape memory behavior and a thermally induced dual shape memory effect. Further study indicated that the material exhibits good triple shape memory behavior. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) demonstrated that the polymer possesses a wide transition temperature, which resulted in excellent dual- and triple-shape memory effects. DSC and swelling experiments were carried out to find that the mechanism of the water-induced shape memory effect involves the decrease of the transition temperature when it swelled in water. Alamar Blue assay showed that the material possesses good biocompatibility and can be potentially used in the field of biomaterials.

Synthesis and properties of magnetic sensitive shape memory Fe3O4/poly(ε‐caprolactone)‐polyurethane nanocomposites

AbstractFe3O4/poly (ε‐caprolactone)‐polyurethane (PCLU) shape memory nanocomposites were prepared by an in situ polymerization method. The thermal properties, magnetic properties, and shape memory properties of the nanocomposites were investigated systematically. The results showed that the Fe3O4 nanoparticles were homogeneously dispersed in the PCLU matrix, which ensured good shape memory properties of nanocomposites in both hot water and an alternating magnetic field (f = 45 kHz, H = 29.7 kA m−1/36.7 kA m−1). The nanocomposites started to recover near 40°C, which is slightly higher than body temperature. Thus, they would not change their deformed shape during the implanting process into the human body. Considering potential clinical applications, 45°C was chosen as shape recovery temperature which is slightly higher than 37°C, and the nanocomposites had high shape recovery rate at this temperature. With increasing content of Fe3O4 nanoparticles, the shape memory properties of the nanocomposites in an alternating magnetic field increased and the best recovery rate reached 97%, which proves that this kind of nanocomposites might be used as potential magnetic sensitive shape memory materials for biomedical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013

Morphology, reversible phase crystallization, and thermal sensitive shape memory effect of cellulose whisker/SMPU nano-composites

To investigate the morphology, crystallization properties of reversible phase and thermal sensitive shape memory properties of CW/SMPU (Cellulose Whisker/Shape Memory Polyurethane) nano-composite, the CW/SMPU nano-composite having CW contents of 0.1–3.8 wt % were prepared. SEM investigation showed the evolution of reversible phase morphology from spherolite crystallization structure to uniform matrix with tiny CW aggregates with the addition of CW into the SMPU matrix. DSC and isothermal crystallization kinetic method revealed the effect of CW on crystallization properties of reversible phase and fixed phase, suggesting that the effect of CW on the crystallization of hard segment phase is not comparable with thermal history; the more CW causes the higher crystallization rate of reversible phase; the crystallization mechanism of reversible phase in nano-composite gradually evolves to heterogeneous nucleation and crystal growth in two dimensions with the increase of CW content; the excellent nucleation effect of CW for the reversible phase leads to the drop of activity energy from 134.1 kJ/mol (N-0), to 95.1 kJ/mol (N-4). Cyclic tensile tests illustrate the addition of CW content can engender rapid shape fixity ability after a relative short cooling time; the shape fixity ratio of nano-composite and the control sample after sufficient cooling all can be identically high. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Thermal sensitive shape recovery and mass transfer properties of polyurethane/modified MWNT composite membranes synthesized via in situ solution pre-polymerization

Polyurethane/multiwalled carbon nanotube (MWNT) composite membranes with thermal sensitive shape memory and mass transfer properties were synthesized via in situ pre-polymerization from concentration pretreated MWNT in DMF ( N, N-dimethylformamide). Composite membranes were made from these polyurethane/MWNT solutions by casting them into Teflon plates. SEM photographs demonstrated that the MWNT distributed relatively homogenously in polyurethane matrix at low content and preferred to align in the membrane 2-dimension plane. The shape recovery and mass transfer properties of the prepared membranes were studied. Thermo-mechanical cyclic tensile testing results suggested that the shape recovery ratio increased prominently at below 2.0 wt% of MWNT because of the MWNTs high interaction with the hard segments; however at 3.0 wt% MWNT content, the shape recovery ratios decreased which can be ascribed to the relatively inhomogeneous distribution of MWNT and the decrease phase separation of the polyurethane at this high MWNT content. The water vapor permeability (WVP) studies showed that at below the soft segment melting transition temperature, at 0.25 wt% MWNT content, the WVP of the composite membrane decreased because the nano-sized MWNT acting as nucleating agent, thus, enhanced soft segment ordered crystal structure. In contrast, with increasing MWNT content, the WVP increased because in one aspect, MWNT constrained the forming of ordered soft segment phase structure; in another aspect, the straight MWNT with large aspect ratios offered a relatively straight “free” pathway for water molecule diffusion on the surface of MWNT or inside MWNT to pass through. At temperature above the soft segment phase melting transition temperature, the WVP increased markedly with increasing MWNT content. This could also be attributed to the pathway effect of MWNT by forming a channel through which water molecules could diffuse rapidly.