Mechanical and scratch behaviors of polyrotaxane‐modified poly(methyl methacrylate)

Self-healing polymers for surface scratch regeneration

Recently, there has been a significant increase in academic and industrial interest in self-healing polymers (SHPs) due to their remarkable ability to regenerate scratched surfaces and materials of astronomical significance. Scientists have been inspired by the magical repairing mechanism of the living world. They transformed the fiction of self-healing into reality by designing engrossing polymeric materials that could self-repair mechanical abrasions repeatedly. As a result, the durability of the materials is remarkably improved. Thus, the idea of studying SHPs passively upholds economic and environmental sustainability. However, the critical areas of self-healing (including healing efficiency, healing mechanism, and thermo-mechanical property changes during healing) are under continuous scientific improvisation. This review highlights recent notable advances of SHPs for application in regenerating scratched surfaces with various distinctive underlying mechanisms. The primary focus of the work is aimed at discussing the impact of SHPs on scratch-healing technology. Beyond that, insights regarding scratch testing, methods of investigating polymer surfaces, wound depths, the addition of healing fillers, and the environmental conditions maintained during the healing process are reviewed thoroughly. Finally, broader future perspectives on the challenges and prospects of SHPs in healing surface scratches are discussed.

Mechanically interlocked polymers based on rotaxanes

The nature of mechanically interlocked molecules (MIMs) has continued to encourage researchers to design and construct a variety of high-performance materials. Introducing mechanically interlocked structures into polymers has led to novel polymeric materials, called mechanically interlocked polymers (MIPs). Rotaxane-based MIPs are an important class, where the mechanically interlocked characteristic retains a high degree of structural freedom and mobility of their components, such as the rotation and sliding motions of rotaxane units. Therefore, these MIP materials are known to possess a unique set of properties, including mechanical robustness, adaptability and responsiveness, which endow them with potential applications in many emerging fields, such as protective materials, intelligent actuators, and mechanisorption. In this review, we outline the synthetic strategies, structure-property relationships, and application explorations of various polyrotaxanes, including linear polyrotaxanes, polyrotaxane networks, and rotaxane dendrimers.

Correlation between Scratch Behavior and Tensile Properties in Injection Molded and Extruded Polymers

This study investigates the validity and applicability of the correlation between scratch and tensile properties for extruded polymer strands. The mechanical properties could be predicted for extruded samples, which allows skipping the step of injection molding and therefore enables a faster material development. Extruded polymer strands and tensile test specimens out of PMMA, PS, POM, PP and PE have been investigated. A correlation of the Young’s modulus and the elastic deformation as well as a correlation of the yield stress and the plastic deformation during scratching is given for both flat molded and cylindrical extruded specimens. SEM images of the scratch grooves are used to analyze the scratch deformation mechanism. The deformation mechanism correlates well to the variation coefficient of the indentation depth. Polarized light microscopy of thin cross sections of both types of specimens provides information about skin layer thickness and morphology. However, the optical analysis could not provide an explanation for the different levels of the indentation depth in the two specimen types. Further investigations should include a study of differences in process induced morphology and the effect of two layers with different mechanical properties, i.e., skin and center, on the stress and strain fields underneath the scratch.

Fracture Behavior of Polyrotaxane-Toughened Poly(Methyl Methacrylate)

The fracture behavior of polyrotaxane (PR)-modified poly(methyl methacrylate) (PMMA) was investigated. PR is a supramolecule with rings threaded onto a linear backbone chain, which is capped by bulky end groups to prevent the rings from de-threading. The ring structure is α-cyclodextrin (CD), and it can be functionalized to enhance its affinity with the hosting polymer matrix. Adding only 1 wt % of PR containing methacrylate functional groups (mPR) at the terminal of some of the polycaprolactone-grafted chains on CD promotes massive crazing, resulting in a significant improvement in fracture toughness while maintaining the modulus and transparency of the PMMA matrix. Dynamic mechanical analysis and atomic force microscopy studies reveal that mPR strongly interact with PMMA, leading to higher molecular mobility and enhanced molecular cooperativity during deformation. This molecular cooperativity may be responsible for the formation of massive crazing in a PMMA matrix, which leads to greatly improved fracture toughness.