Shape Memory Polymers, Blends and Composites

This chapter provides an overview of shape-memory polymers and their blends and composites. The history of shape-memory polymers, their advantages, shape-memory cycles, classification and the molecular mechanism of the shape-memory effect are briefly discussed. The characterisation techniques such as dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical and polarized optical microscopy (OM and POM), atomic force microscopy (AFM), laser scanning confocal microscopy (LSCM), universal testing machine (UTM), nanoindentation technique, etc., are powerful techniques to investigate the shape-memory mechanism and shape-memory performance. Shape-memory polymers have myriad of potential applications in automobile, sports products and textile, aerospace and medical fields.

Since the last three decades, international research interest into the shape-memory effect in polymers has been rapidly growing. The recent progresses made in the synthesis of different types of shape-memory polymers (SMPs) significantly expanded the practical potential of their applications in such fields like microelectromechanical systems, medical and biomimetic devices, sensors, actuators, self-healing systems, etc. The present chapter is focused on the classification of shape-memory polymeric materials (SMPs), as well as the current developments and most important concepts for these types of smart polymers. The recent progress in the development of shape-memory polymer composites (SMPCs) and shape-memory polymer blends (SMPBs) is also highlighted. In this chapter, different classification criteria of SMPs with a view to polymer type and structure and external stimulus are described. Particular emphasis is placed on the factors enabling shape-memory effects, especially structure–property correlations that influence shape-memory mechanisms.

Shape-memory polymers (SMPs) are one type of smart materials that are capable to recover from a “fixed” temporary shape to a “memorized” original shape under external stimulus. This chapter provides a comprehensive overview about the preparation methods of shape-memory polymers, polymer blends, and composites. Following a brief introduction of SMPs, the strategies for the preparation of conventional SMPs such as chemical cross-linking of thermoplastic polymers, single-step polymerization of monomers/prepolymers with cross-linkers, one-step synthesis of phase-segregated block copolymers are reviewed. Next, the notable recent progress in SMP blends are systemically studied including direct blending of different polymers, addition of a third component into blends, novel processing methods, etc. Third, the researches in SMP composites including reinforcement effect, indirect thermal stimuli-responsive effects, novel shape-memory effect, and functional applications are discussed. Finally, the current challenges and future advancements of SMP blends and composites are proposed.

Shape-memory polymers (SMPs) have attracted considerable attention in recent decades due to the characteristics of switching from permanent shape to temporary shape and vice versa by the application of an external stimulus. The significance and diverse applications of SMPs in the scientific and commercial scope generate researchers to have keen knowledge in the manufacturing of new shape-memory polymers and their blends and composites with improved thermomechanical and other desired properties. This chapter will provide a generalized view on the rheology of SMPs and their blends and composites that would give a holistic picture of this promising area of research.

Contemporary microscopes can magnify almost everything that is invisible to the naked eye, down to the atomic level. Current classifications include optical microscopy, electron microscopy, and scanning probe microscopy, in which optical one focuses on microscale while electron and scanning probe ones focus on the nanoscale. Microscopy is an indispensable technique of characterization for shape memory polymers (SMPs), including optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), infrared microscopy, fluorescence microscopy, and laser scanning confocal microscopy (LSCM). In this chapter, the micro- and nanostructures of different shape memory polymers, blends, and composites will be discussed. The applications of these microscopical techniques will be outlined. A brief account of various types of morphologies and their impact on shape memory effects will be provided.

This chapter is dedicated to the dynamical mechanical thermal analysis of shape-memory polymers. Temperature obviously plays a major role in the mechanical properties of these materials; hence, the understanding of the physical phenomena driving the shape-memory effect is of first importance for the design of practical applications in which shape-memory polymers are used. The shape-memory effect being closely related to the viscoelastic behavior of the polymer, it is important to properly describe it with appropriate tools. The objective of this chapter is to describe characterization methods, models, and parameters identification techniques that can be easily used for the description of the thermomechanical behavior of SMPs. The associated models can easily be implemented in finite element codes for time- or frequency-domain simulations. The experimental results and all numerical values of the models are provided for three shape-memory polymers: the tBA/PEGDMA and a vitrimer, which can easily be manufactured according to the data provided in open literature, and a shape-memory polymer filament for 3D printing, which is available on the shelf.

Calorimetry is the primary technique for measuring the thermal properties of materials. From calorimetric methods, it is possible to perform a correlation between temperature, structure, and the physicochemical properties of the materials. The differential scanning calorimeter (DSC) is one of the most common methods used to determine the thermal properties in polymeric materials. To determine the thermal properties of thermally activated polymeric materials is fundamental for the development of the programming cycle of these materials. This chapter presents a brief discussion about the application of the DSC in determining the thermal transitions of the materials and its correlation with the structure and memory effect.

This chapter will focus on the thermal analysis and interesting related properties of high performance shape memory polymers (SMPs), shape memory polymer blends (SMPBs), and shape memory polymer composites (SMPCs) in different length scales. In general, thermal behaviors of shape memory materials are very relevant to the potential uses in many demanding applications. In order to develop durable industrial products, it is necessary to investigate the thermal stability of these polymers. The polybenzoxazine (PBZ)-based shape memory materials are mainly mentioned in this chapter due to the outstanding properties and high thermal stability of the novel phenolic polymers. This kind of thermoset can be alloyed with other polymers such as epoxy and polyurethane suitable to be used to produce SMPCs in high temperature applications with synergistic behaviors. Therefore, the PBZ/epoxy alloy-based systems and PBZ/polyurethane alloys-based systems are mentioned as well.

Shape-memory polymers (SMPs) are widely employed in aerospace, biomedical, portable electronic devices, etc., where their multiple-shape capabilities are considered. In order to avoid the failure of the SMPs before shape change, it is critical to possess excellent mechanical properties along with their inherent shape-memory ability. Recent research reports highlight the importance of SMPs with high strength and toughness. Conventional mechanical testing procedures such as tensile, bending, and fracture toughness are used to outline the static mechanical performance of SMPs. The cyclic mechanical testing facilitates the evaluation of shape-memory parameters such as shape fixity (R_f) and shape recovery (R_r) ratio. In a recent development, nanoindentation technique is used to probe the shape-memory process at nanolevel. SMPs based on epoxy, polyurethane, PCL, etc., were investigated for their both static and cyclic mechanical performance. Well-balanced mechanical and shape-memory performance can be tailored in SMPs by careful tuning of crystallinity, cross-link density, and fiber/filler reinforcement.

Biodegradable shape-memory polymers (BSMP) have arisen as highly promising materials for biomedical applications due to their valuable properties. Their chemical and structural diversities, low toxicity, biodegradation, and resorption added to their capability to adapt their shape due to their shape-memory property make them excellent materials for many implantable devices. In this chapter, the main characteristics of these materials and their applications in biomedicine are described.

The polymeric shape-memory materials, which generally trigger the shape-memory effect (SME) via direct heating, have been the rising star in the field of smart materials. Recently, numerous efforts have been paid to explore the alternative methods for realizing SME by indirect actuation, for further extending the practical application. Incorporation of functional groups or/and fillers is the most convenient route to endow the shape-memory matrix with enhanced properties of inductive heating, which has been rapidly developed to achieve new stimulus-responsive behavior. Herein, the novel functions of the shape-memory polymers, polymer blends, and composites including optical, electrical, and magnetic properties will be introduced. Moreover, the operative mechanism and optimization method of the different properties will be substantially discussed considering the composition change, morphology control, and structure design as well as the filler type, concentration, and dispersion. Finally, an outlook is presented describing the future challenges of this promising field.

Shape memory polymers experience stress-induced macromolecular reorganization like alignment, crystallization, isotropic-to-smectic order, and temperature-induced melting (disorder), crystallization (ordering). The molecular processes involve short and/or long-range order. Hence, there is a need to apply suitable multi-scale characterization techniques to assess the molecular changes occurring during shape memory events. Ideally, the spatial resolution ranges from Å to nm- to μm-scale. This chapter focuses on the application of wide-angle and small-angle X-ray scattering (WAXS and SAXS, respectively), small-angle light scattering (SALS) and optical microscopy techniques which are ideal to get insights into the molecular mechanisms associated to shape memory in polymers. These techniques are ideally suited to enable in situ and time-resolved studies. It is the author’s view that understanding the molecular mechanisms is at the heart of shape memory effects and novel in situ techniques and simultaneous monitoring of microstructure and bulk extensional properties during shape memory cycles need to be implemented. The main body of the chapter focused on fundamentals of X-ray scattering, recording techniques, and applications to the study of shape memory polymers using conventional X-ray sources and synchrotron radiation. WAXS and SAXS enable Å- and nm-scale structure analysis and synchrotron sources enable time-resolved resolution. On the other hand, in situ and time-resolved studies of microstructure at μm-scale are enabled by optical microscopy and SALS. These techniques combined with temperature or uniaxial testing are also a powerful tool to understand molecular mechanisms associated to shape memory behavior.

In this chapter, applications of Shape-Memory Polymers (SMPs), and their blends and composites (SMPCs) are discussed. SMPs and SMPCs are a new class of stimuli-responsive smart materials that change their configuration reacting to specific external stimulus and remember the original shape. They are expected to have interesting applications in many engineering fields such as aerospace (e.g., in deployable structures and morphing wings), microelectronics (e.g., in flexible bioelectronics and active disassembly systems), automotive (e.g., automobile actuators and self-healing composite systems), and biomedical one (e.g., in stents and filters). This is mainly due to their lightweight, high shape reconfiguration, recovery force, good manufacturability, easily tailorable glass transition temperature, and low cost. After a brief description of SMPs, blends and their composites behavior, this chapter highlights the most attractive current and future applications.