Physicochemical WPC Modification Techniques

Structure and Drug Release in a Crosslinked Poly(Ethylene Oxide) Hydrogel

Magnetoactive polymer compositesЁ— polymer matrices with embedded magnetic micro- and/or nanoparticlesЁ— belong to the class of «smart» materials and currently attract significant fundamental and practical interest. This article focuses primarily on magnetoactive elastomers (MAEs) based on chemically crosslinked polymer systems, research on which has been conducted at the Physics Faculty of Moscow State University since the late 1990s. A definition of MAEs is provided, and the properties of their main components — the polymer matrix and magnetic particles — are described. An overview is given of the physical phenomena observed in these materials when an external magnetic field is applied. The influence of the material composition on its magnetic response is discussed in detail, with an emphasis on magnetomechanical properties, which are most critical for practical applications. The results of recent studies related to the synthesis of new matrices for MAEs, the influence of the shape and distribution of magnetic particles in the polymer matrix, as well as contemporary theoretical approaches to describing the behaviour of MAEs in an external magnetic field are analyzed. Finally, the prospects for further advancement in the development of magnetoactive polymer materials and their practical applications are discussed.

13 - Polymer nanocomposites for biomedical applications

The effect of conductive network on positive temperature coefficient behaviour in conductive polymer composites

Nanostructures derived from structural polysaccharides, such as cellulose and chitin, are notable for their sustainability, lightweight properties, and superior mechanical attributes. The macroscopic performance of these materials largely depends on the orientation of nanostructures. This study explores the preferential orientation of chitinous nanofibers (NFs) within a thermoplastic polymer matrix (PM) comprising poly(N‐vinylpyrrolidone) and glycerol, achieved through dry thermal stretching techniques. Altering the PM composition enables the modulation of the system's glass transition temperature (Tg). Chitin NFs are effectively dispersed within the PM, with their orientation enhanced by stretching at temperatures ≈30 °C above the Tg of the composites, resulting in an elongation at rupture (ε) of 105%. Under similar temperature conditions, composites with chitosan NFs show strong interactions with the PM, hindering the stretching process (ε = 10%). In contrast, composites with acetylated chitin NFs demonstrate increased stretchability (ε = 170%) but have insufficient interactions to stabilize their orientation. These interactions, identified as hydrogen bonds through FTIR, vary significantly based on the functional groups present on the NF surfaces. This variation is supported by DSC and dynamic mechanical analysis. Oriented ChNFs hold potential for bioactive applications.

The addition of nanoparticles into organic polymers provides an efficient means to advance the properties of the host polymer. The properties of such polymer nanocomposites are built upon the nanoparticles that are dispersed within the polymer matrix. However, because of inaptness, the dispersion of synthesized inorganic nanoparticles in polymer matrices is very challenging; this paper reports the synergistic effect of the use of silica, thermal and chemical modification to improve the dispersion of carbon black (CB) nanoparticle in epoxy resin. The properties of the nanoparticles and the epoxy nanocomposite were investigated using XRD, XPS, FESEM, FTIR, BET/SAP and particle size zetasizer. The addition of silica and the use thermal and chemical modification proved a FESEM image with a well dispersed CB nanoparticle within the host epoxy resin.

Carbon nanotubes (CNTs) based polymer composites have variety of engineering applications (electromagnetic shielding, antistatic coatings, high-strength low-density corrosion-resistant components, lightweight energy storage and many more); due to their excellent mechanical, electrical, chemical, magnetic, etc. properties. In the polymer nanocomposites CNTs are dispersed in the polymeric matrix. However the dispersion may be uniform or may not be uniform. The biggest challenge is the effective dispersion of individual CNTs in the polymer matrices, as CNTs tends to form clusters and bundles due to strong van der Waals’ forces of attraction. The aggregated structure continue until physical (Mechanical) or chemical modification (Encapsulation/surface modification) of CNTs. Few modification methods such as vigorous mixing of the polymers damages CNTs structure, and may hinder their properties. But these problems can be overcome by mechanical or chemical modification of CNTs surfaces. In the chemical modification, the modifier or the long tail surfactant may encapsulate and/or partially wrap the CNTs surfaces. In this review, recent work on CNTs based polymer nanocomposite is carried out with few modifiers/encapsulating agents. Incorporation of CNTs in polymer matrix changes the performance properties such as tensile strength, tensile modulus, elongation at break, toughness, Dynamic mechanical thermal analysis (DMTA), etc. The phase morphology of the composite materials throws light on the properties of CNTs based polymer nanocomposite. Moreover phase morphology may be directly correlated with the behavior of the material, hence reviewed here through transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Furthermore review is also carried out on the non-isothermal crystallization (DSC) and rheology of CNTs polymer nanocomposite.

Nowadays special attention is given to the so-called "smart-materials" or "intellectual" materials, which have the ability to purposefully change their physical and physical-chemical properties depending on changing external conditions. Сonductive conjugated polymers - polyaniline (РАNi) and its derivatives may alter their properties in response to external action - exhibit sensory sensitivity, electrochromic, thermochromic and solvachromic effects. When creating РАNi composites with industrial polymer matrices, an important issue is to determine the physical and mechanical properties, in particular, of microhardness as a material strength characteristic. Composite samples were obtained by the method of thermal pressing of highly dispersed powders of conductive polymers dispersed in polymer matrices. The mechanical properties of the composites were studied by the method of measuring microhardness and boundary microhardness on a Heppler consistometer. The determination of the electrical conductivity of the composites in the molded samples was determined by the standard 2-contact method at a temperature T = 293 K. The influence of the acid doped polyaniline (РАNi) as an conductive polymer filler оn on the microhardness of composites with polymer matrices of different structure (polyvinyl alcohol (PVA), polymethylmethacrylate (PMMA), polybuthylmethacrylate (PBMA), epoxy resin ED-20) was studied. It is found that the nature of the interaction between the polymer matrix and the conductive polymer filler depends on its content and the structure of the matrix, which is manifested in the growth of microhardness for composites PBMA – РАNi and ED-20 - РАNi and its reduction for composites PVA– РАNi at the contents of the filler 5-20 %. The dielectric polymer matrix preserves the properties inherent in both high polymers (high elasticity, thermoplasticity) and the semiconductor nature of the electrical conductivity inherent in the conjugated polymers. The value of the specific conductivity of the composites obtained well correlated with changes in microhardness, which is a confirmation of the enhancing or loosening nature of the interaction between the polymer matrix and the conductive polymeric filler.

The average pull-out force and interaction energy of polyethylene (PE) cross-linked functionalized carbon nanotubes (cfCNTs) embedded in polymer matrices (PE-cfCNTs@polymers) was studied using molecular dynamics (MD) simulations. Accordingly, the pull-out process of PE-cfCNTs from inside polymer matrices, i.e., Aramid and PE, was performed under displacement control. The results obtained were compared with those of pure carbon nanotube (CNT) incorporated into polymer matrices (pure CNT@polymers). The influence on the pull-out force and interaction energy between the CNT and polymer of the structure of polymer matrices, the weight percentage and two types of distribution patterns of cross-linked PE chains, namely mapped and wrapped, was investigated. The results indicate that the structure of the polymers and distribution patterns of cross-linked PE chains strongly affect important parameters related to interfacial properties. The average pull-out force of mapped and wrapped PE-cfCNTs@polymers increases as the weight of attached PE chains on the CNT surface increases. The effect of wrapped structures on increasing the pull-out force is greater than that of the mapped configurations. Also, the PE-cfCNTs@polymers show higher average pull-out forces than those of their pure counterparts. As the CNT pulls out from the polymer matrix, an approximately linear reduction in the absolute value of interaction energy with the pull-out displacement is observed. However, this trend is changed to some extent by imposing instability through the wrapped PE-cfCNTs.

Photophysics of 2,6-bis(4′-diethylaminobenzylidene)cyclopentanone in a polymer matrix containing carboxyl groups

PSS)/nanographite nanocomposite (NC) films prepared by the solution blending method were irradiated with SHI (Ni ion beam, 80 MeV) at a fluence range of 1 × 10(10) to 1 × 10(12) ions/cm(2). XRD studies revealed that ion irradiation results in delamination and better dispersion of NGPs in the irradiated nanocomposite films compared to unirradiated films, which is also depicted through SEM, AFM, TEM, and Raman studies. In the irradiated polymer nanocomposite films, the conformation of PEDOT chains changes from coiled to extended coiled structure, which, along with homogeneously dispersed NGPs in irradiated NCs, shows an excellent synergistic effect facilitating charge transport. The remarkable improvement in conductivity from 1.9 × 10(-2) in unirradiated NCs to 0.45 S/cm in irradiated NCs is observed with marked improvement in sensing the response toward nitroaromatic vapors at room temperature. The temperature induced conductivity studies have been carried out for PSS/nanographite NCs to comprehend the charge transport mechanism in NC films using the 3D Mott variable range hopping model also. The study reveals SHI as a novel method, addressing the challenge associated with the dispersion of NGPs within the polymer matrix for their enhanced performance toward various applications.

It has been found that polymer composites possess advanced mechanical and thermal performances after being loaded with functional/reactive bio or mineral fillers. The high bonding strength between the polymer matrix and the fillers represents a crucial factor for obtaining a good reinforcement in the composite materials. Many techniques have been developed for chemical functionalization of the filler surface to improve its bonding strength, compatibility and dispersibility within polymer matrices, and also to prevent deterioration of the structure. Thus, reactive cross-linkable groups showing high reactivity toward the target functional groups of the polymer matrix have been attached to the filler surface. However, the introduction of reactive residues onto the filler surface, such as vinyl and epoxy functionalized molecules, provides polymerizable centers convenient for copolymerization with corresponding groups in monomer chains. This chapter aims to present a comprehensive review of various chemical modification techniques applied to obtain reactive cross-linkable bio and mineral fillers suitable for copolymerization with polymer matrices. It also covers the analysis of the processing and reinforcement properties of reactive polymer/modified filler-based composites.

Directional alignment of carbon nanotubes in polymer matrices: Contemporary approaches and future advances

Polymer matrices are commonly used as guest-host systems for organic chromophores for use in non-linear optical materials. The chromophores must be aligned or poled in an electric field in order to impart anisotropy and non-linear activity to the material. This poling process raises several issues, the two largest being the eventual relaxation of the chromophores back into random orientations due to brownian motion, and high molecular weight polymer matrices limiting chromophore mobility during poling. The prevention of this relaxation process is an area of significant interest, especially in applications that require long term coating stability and activity. In this study, a polymer matrix is synthesized that seeks to solve both of these problems with one system. The ideal system would be one that allows for chromophore mobility during processing, but once chromophores have reached the desired orientation, limits mobility and relaxation during in-service usage. A copolymer of methyl methacrylate and a Diels-Alder adduct cross-linking monomer was synthesized in order to meet these challenges. This polymer was blended with commercially available acrylic polymer and organic chromophore molecules in order to test the viability of the solution. It was found that at the percent composition of cross-linker being utilized in the study, the Diels-Alder linkages were not reforming in any measurable amount due to the low amount of Diels-Alder active monomer units. This led to the development of a new system based on mixing polyfuran based polymers with polymaleimide based polymers during processing. This method allows for high amounts of cross-linking after processing ceases, which achieves both initial goals of the project, as well as allowing facile synthesis of the desired polymer components. Another attempt to address these issues in polymer matrix formation led to the use of a novel inimer system. The cross-linking agent was also the polymerization initiator, and these functionalities were separated by a Diels-Alder linkage that would fall apart upon exposure to thermal stimulus. These polymers were synthesized and isolated easily, although in some cases gelation occurred. In order to observe the extent of the cross-linking inimer being incorporated into the matrix, cleavage experiments were performed to induce the breaking of the Diels-Alder adduct. Analyzing the Diels-Alder cleaved polymer led to an interesting result: all polymers showed an increase in apparent molecular weight when analyzed by gel permeation chromatography. The increase in molecular weight occurring upon cleavage of main chain bonds has never before been observed in literature.

Enabling efficient and ultralong room-temperature phosphorescence from organic luminogens by locking the molecular conformation in polymer matrix