Polymers and Related Composites via Anionic Ring-Opening Polymerization of Lactams: Recent Developments and Future Trends.

This paper presents a comprehensive overview of polymers and related (nano)composites produced via anionic ring opening polymerization (AROP) of lactams. It was aimed at surveying and showing the important research and development results achieved in this field mostly over the last two decades. This review covers the chemical background of the AROP of lactams, their homopolymers, copolymers, and in situ produced blends. The composites produced by AROP were grouped into nanocomposites, discontinuous fiber, continuous fiber, textile fabric, and self-reinforced composites. The manufacturing techniques were introduced and the most recent developments highlighted. Based on this state-of-art survey some future trends were deduced and as their "driving forces" novel and improved manufacturing techniques identified.

One-Pot Synthesis and Characterization of Novel Shape-Memory Poly(ε-Caprolactone) Based Polyurethane-Epoxy Co-networks with Diels⁻Alder Couplings.

The present work aimed at the preparation and investigation of different epoxy-polyurethane (EP-PU) co-networks. The EP-PU co-networks were obtained by applying two different synthetic strategies, in which the coupling element, the Diels⁻Alder (DA) adduct, was prepared previously or formed "in situ" in the reaction between furan functionalized polyurethane and furfuryl amine-diglycidyl ether bisphenol-A oligomers (FA_DGEBA). For the synthesis of these EP-PU networks, poly(ε-caprolactone)-diol (PCD, Mn = 2 kg/mol) and poly(ε-caprolactone) (PCL) with different molecular weights (Mn = 10, 25 and 50 kg/mol) and 1,6-hexamethylenediisocyanate (HDI) were used. The EP-PU co-networks were characterized by Attenuated Total Reflectance Fourier-Transform Infrared spectroscopy (AT-FT-IR), differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA). Scanning electron microscopy (SEM) was applied to assess the morphology of the EP-PU samples. It was demonstrated that the stress⁻strain curves for the EP-PUs could be interpreted based on the Standard Linear Solid (SLS) model. The DMA traces of some EP-PUs (depending on the composition and the synthetic method) revealed a plateau-like region above the melting temperature (Tm) of PCL confirming the presence of cross-linked structure. This feature predicted shape memory (SM) behavior for these EP-PU samples. Indeed, very good shape fixity and moderate shape recovery were obtained. The shape recovery processes of these EP-PU samples were described using double exponential decay functions.

Microwave Devulcanized Crumb Rubbers in Polypropylene Based Thermoplastic Dynamic Vulcanizates.

Because of the chemically crosslinked 3D molecular structure of rubbers, their recycling is a challenging task, especially when cost efficiency is also considered. One of the most straightforward procedures is the grinding of discarded rubber products with subsequent devulcanization. The devulcanized rubber can be used as a feedstock for fresh rubber compounds or can be blended with uncured virgin rubber and thermoplastic polymers to form thermoplastic dynamic vulcanizates (TDVs). TDVs combine the beneficial (re)processability of thermoplastics and the elastic properties of rubbers. Our current work focuses on the development of polypropylene (PP)-based TDVs with the use of a tire model rubber (MR) composed of natural rubber (NR) and styrene-butadiene rubber (SBR) in a ratio of 70/30. The research target was the partial substitution of the above fresh MR by microwave devulcanized crumb rubber (dCR). TDVs were produced by continuous extrusion, and the effects of composition (PP/MR/dCR = 40/60/0…50/35/15) and processing parameters (different screw configurations, temperature profiles, the feeding method of PP) were investigated. Results showed that the fresh rubber compound can be replaced up to 10 wt % without compromising the mechanical properties of the resulting TDV.

Characterization of layered silicate-reinforced blends of thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate).

A two-step melt blending procedure was used to produce binary systems composed of thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT). To improve the properties of the blends, two different layered silicates, viz. bentonite (BT) and organically modified montmorillonite (oMMT) were incorporated. First, TPS and its layered silicate nanocomposites were prepared via extrusion compounding during which starch was plasticized with glycerol and water. In the second step, PBAT was added to TPS/layered silicate to produce blends in a batch-type mixer. Mechanical and thermal properties were determined. The blends showed acceptable ductility over 50wt.% PBAT content, although at the cost of strength and stiffness. By contrast to oMMT the BT became intercalated in TPS and TPS/PBAT blends. The reinforcing effect of BT and oMMT was most prominent for the glassy states of both TPS and TPS/PBAT blends. Thermal, and thermooxidative properties were not significantly affected by the presence of layered silicates.

Review of Progress in Shape Memory Epoxies and Their Composites.

Shape memory polymer (SMP) is capable of memorizing one or more temporary shapes and recovering successively to the permanent shape upon various external stimuli. Beside of the above mentioned one-way variants, also two-way shape memory polymers (SMPs) and shape memory (SM) systems exist which feature a reversible shape change on the basis of "on-off switching" of the external stimulus. The preparation, properties and modelling of shape memory epoxy resins (SMEP), SMEP foams and composites have been surveyed in this exhaustive review article. The underlying mechanisms and characteristics of SM were introduced. Emphasis was put to show new strategies on how to tailor the network architecture and morphology of EPs to improve their SM performance. To produce SMEPs novel preparation techniques, such as electrospinning, ink printing, solid-state foaming, were tried. The potential of SMEPs and related systems as multifunctional materials has been underlined. Added functionality may include, among others, self-healing, sensing, actuation, porosity control, recycling. Recent developments in the modelling of SMEPs were also highlighted. Based on the recent developments some open topics were deduced which are merit of investigations in future works.

Surface tailored PS/TiO2 composite nanofiber membrane for copper removal from water.

Polystyrene (PS)/TiO2 composite nanofiber membranes have been fabricated by electrospinning process for Cu(2+) ions removal from water. The surface properties of the polystyrene nanofibers were modulated by introducing TiO2 nanoparticles. The contact angle of the PS nanofiber membrane was found to be decreased with increasing concentration of TiO2, depicted enhanced hydrophilicity. These membranes were highly effective in adsorbing Cu(2+) ions from water. The adsorption capacity of these membranes was found to be 522 mg/g, which is significantly higher than the results reported by other researchers. This was attributed to enhanced hydrophilicity of the PS/TiO2 composite nanofiber membranes and effective adsorption property of TiO2 nanoparticles.

Water-Assisted Production of Thermoplastic Nanocomposites: A Review.

Water-assisted, or more generally liquid-mediated, melt compounding of nanocomposites is basically a combination of solution-assisted and traditional melt mixing methods. It is an emerging technique to overcome several disadvantages of the above two. Water or aqueous liquids with additives, do not work merely as temporary carrier materials of suitable nanofillers. During batchwise and continuous compounding, these liquids are fully or partly evaporated. In the latter case, the residual liquid is working as a plasticizer. This processing technique contributes to a better dispersion of the nanofillers and affects markedly the morphology and properties of the resulting nanocomposites. A survey is given below on the present praxis and possible future developments of water-assisted melt mixing techniques for the production of thermoplastic nanocomposites.

Epoxy/Polycaprolactone Systems with Triple-Shape Memory Effect: Electrospun Nanoweb with and without Graphene Versus Co-Continuous Morphology.

Triple-shape memory epoxy (EP)/polycaprolactone (PCL) systems (PCL content: 23 wt %) with different structures (PCL nanoweb embedded in EP matrix and EP/PCL with co-continuous phase structure) were produced. To set the two temporary shapes, the glass transition temperature (Tg) of the EP and the melting temperature (Tm) of PCL served during the shape memory cycle. An attempt was made to reinforce the PCL nanoweb by graphene nanoplatelets prior to infiltrating the nanoweb with EP through vacuum assisted resin transfer molding. Morphology was analyzed by scanning electron microscopy and Raman spectrometry. Triple-shape memory characteristics were determined by dynamic mechanical analysis in tension mode. Graphene was supposed to act also as spacer between the nanofibers, improving the quality of impregnation with EP. The EP phase related shape memory properties were similar for all systems, while those belonging to PCL phase depended on the structure. Shape fixity of PCL was better without than with graphene reinforcement. The best shape memory performance was shown by the EP/PCL with co-continuous structure. Based on Raman spectrometry results, the characteristic dimension of the related co-continuous network was below 900 nm.