Xuelian Wu

Effect of a linear monomer on the thermomechanical properties of epoxy shape-memory polymer

The effect of a linear monomer on thermomechanical properties and shape recovery behavior of an epoxy shape-memory polymer is studied. These shape-memory polymers are prepared from epoxy base resin, hardener and linear epoxy monomer. As the content of the linear monomer increases, the glass transition temperature (Tg) determined using differential scanning calorimetry ranges from 37 to 96 °C. A decrease in rubber modulus is seen from dynamic mechanical analysis for the polymers, which reveals decreasing crosslink density with increasing linear monomer content. Tensile test results show that the elongation at break and strength depends on the content of linear monomer at Tg or Tg−20 °C, while the linear monomer content has minor influence on elongation at break and strength at Tg+20 °C. Finally, investigation on shape recovery behavior reveals that full recovery can be observed for each polymer when the temperature is equal to or above Tg. Also, increasing the linear monomer content results in a decrease in both shape recovery ratio (below Tg) and shape recovery speed (at Tg). These results are interpreted in terms of various crosslink densities attributed to the increasing linear monomer content.

Characterization of shape recovery via creeping and shape memory effect in ether-vinyl acetate copolymer (EVA)

Shape recovery in a commercial ether–vinyl acetate copolymer (EVA) was systematically characterized by studying its creep and the thermoresponsive shape-memory effect (SME). The influences of the programming temperature and maximum uniaxial tension strain on the shape-fixity ratio and the shape-recovery ratio were investigated quantitatively. In addition to excellent SME, high elasticity and high creep were observed at around room temperature (with the EVA in the glassy state). The underlying mechanisms for the different shape-recovery phenomena (i.e., creep and the SME) are discussed. Two potential applications utilizing the shape-recovery property and high elasticity of this EVA are presented.

Heating/ethanol-response of poly methyl methacrylate (PMMA) with gradient pre-deformation and potential temperature sensor and anti-counterfeit applications

In this paper, the heating/ethanol-response of a commercial poly methyl methacrylate (PMMA) is investigated. All PMMA samples are pre-deformed by means of impression (surface compression with a mold) to introduce a gradient pre-strain/stress field. Two types of molds are applied in impression. One is a Singaporean coin and the other is a particularly designed mold with a variable protrusive feature on top. Two potential applications—temperature sensors to monitor overheating temperatures and anti-counterfeit labels with a water-mark that appears only upon heating to a particular temperature—are demonstrated. Since the heating-responsive shape memory effect (SME) is an intrinsic feature of almost all polymers, other conventional polymers may be used in such applications as well.

Two-step shape recovery in heating-responsive shape memory polytetrafluoroethylene and its thermally assisted self-healing

In this paper, the heating-responsive shape memory effect (SME) in commercial polytetrafluoroethylene (PTFE) programmed by means of tension and compression is investigated systematically. The focus is on the influence of the glass transition (Tg) and the melting transition (Tm) on the shape recovery performance. Two-step shape recovery upon heating to over the glass transition range and then the melting transition range is observed. The key parameters in programming, namely the programming temperature, programming strain and deformation method, are examined. In addition, we study the feasibility of utilizing the high melting temperature nature of PTFE as a high temperature shape memory polymer (SMP) and for thermally assisted self-healing.

Effect of the γ-radiation on the properties of epoxy-based shape memory polymers:

In this article, the epoxy-based shape memory polymers were exposed to simulated γ-radiation environments up to 140 days for an accelerated irradiation. The influence of γ-radiation on thermal and mechanical properties was evaluated by differential scanning calorimetry, dynamic mechanical analysis, and tensile test. The glass transition temperatures (Tg) determined by differential scanning calorimetry and dynamic mechanical analysis decreased no more than 10%, and the shape recovery speed became a little faster after γ-radiation of 1 × 105 Gy. The tensile strength and elastic modulus could, respectively, maintain 26 MPa and 1.36 GPa after being irradiated by 1 × 106 Gy radiation, showing great potential in aerospace structural materials.

Characterization of polymeric shape memory materials

Abstract After a short discussion of various shape memory related phenomena and the basic working mechanisms behind the shape memory effect (SME) in polymeric shape memory materials (SMMs), standard techniques and procedures to characterize these types of materials are reviewed in details (including the concerns in the selection of testing methods and parameters). Although the focus of this paper is on the heating-responsive SME, important issues in the chemo-responsive SME are addressed. Furthermore, some other shape memory related phenomena, such as various kinds of temperature memory effect (TME), and multiple-SME etc., and optimization of the shape memory performance of a shape memory polymer (SMP) via tailoring the programming parameters are included.

Study on Shape Recovery Behaviors of Epoxy-Based Shape Memory Polymer

The glass transition temperatures of epoxy-based shape memory polymers (SMPs), which contain a flexibilizer at various contents of 0%, 5%, 10% and 15% respectively, are determined through DMA tests. The shape memory effect of such materials is investigated through shape recovery experiments. Experimental results show that the content of flexibilizer has much influence on the shape memory effect of epoxy-based SMP. A shape recovery equation is developed based on the results of shape recovery experiment. Numerical calculations show that the developed shape recovery equation well predicts the shape recovery behaviors of epoxy-based SMP.

A preliminary study on shape recovery speed of a styrene-based shape memory polymer composite actuated by different heating methods

Thermally activated shape memory polymers (SMPs) receive increasing attention in recent years. Different from those reported in the literature, in this paper we propose a new approach, i.e., using infrared light, for heating SMPs for shape recovery. We compare this approach with the traditional water bath method in terms of shape recovery speed in bending at both vacuum and no vacuum conditions. The results reveal that the shape recovery speed in infrared heating at vacuum condition is about eight times slower than that by hot water. However, the recovery time is more than doubled if without vacuum.

THERMOMECHANICAL PROPERTY OF EPOXY SHAPE MEMORY POLYMERS

Epoxy shape memory polymers (SMPs) were preparation and their mechanical properties are focused on. Full shape recovery is observed at 150 °C for each polymer, and the SMP with lower hardener content shows a quicker shape recovery speed. In addition to a good thermal stability, glass transition temperature of the polymers increases with increasing hardener content. Of particular attention of DMA test is that the epoxy SMPs show a high storage modulus not only in glass state but also in rubber state. The tension test indicates that both stress at break and corresponding elastic modulus vary with a peak value for the polymers.

Investigation of mechanical behavior of epoxy shape memory polymers

Shape memory polymer (SMP) is a new class of smart material which attracts great interest in recent years. In this paper, in addition to the synthesizing of three types of epoxy SMPs with various linear epoxy monomer contents, their mechanical properties are focused on. Structure characteristic, dynamic mechanical property and quasi-static tension property and shape memory behavior of the epoxy SMPs are presented. Results indicate that glass transition temperature determined by dynamic mechanical analysis (loss modulus) varies from 69 to 113 °C for the epoxy SMPs. And it should be noted that the linear monomer has no effect on storage modulus in glass state but decrease the storage modulus in rubber state for the polymers. From tensile test, it is found that the content of linear monomer has significant effect on the tensile deformation behavior which varies from a brittle response to elastomeric response at room temperature. And the strength varies from 15 to 62MPa with the corresponding elastic modulus ranging from 2.5 to 1.7GPa for the epoxy system. Characterization of the shape memory effect in epoxy SMP suggests a high (above 99%) shape recovery ratio at 100 °C, besides, the epoxy SMP with higher linear monomer content shows a quicker shape recovery speed. Moreover, effect of linear monomer content on glass transition temperature and thermo-mechanical property is also investigated. Results indicate that, epoxy SMP fabricated in this study possess not only unique shape memory effect but also excellent mechanical properties, which will be the leading candidate for applications in engineering fields.