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Shear-induced formation of crystal nuclei in polyamide 11 (PA 11) was studied using a conventional parallel-plate rheometer. Crystallization of PA 11 after shearing the melt at different rates for 60 s was followed by the evolution of the complex viscosity. The sheared samples showed in an optical microscope a gradient structure along the radius, due to the increasing shear rate from the center to the edge. The critical shear rate for shear-induced formation of nuclei was identified at the position where a distinct change of the semicrystalline superstructure is observed, being at around 1 to 2 s−1. Below this threshold, a space-filled spherulitic superstructure developed as in quiescent-melt crystallization. Above this value, after shearing at rates between 1 and 5 s−1, an increased number of point-like nuclei was detected, connected with formation of randomly oriented crystals. Shearing the melt at even higher rates led to a further increase of the nuclei number and growth of crystals oriented such that the chain axis is in parallel to the direction of flow. In addition, optical microscopy confirmed formation of long fibrillar structures after shearing at such condition. The critical specific work of flow of PA 11 was calculated to allow a comparison with that of polyamide 66 (PA 66). This comparison showed that in the case of PA 11 more work for shear-induced formation of nuclei is needed than in the case of PA 66, discussed in terms of the chemical structure of the repeat unit in the chains. Graphical abstract

Biodegradable polylactide/modified polycaprolactone (PLA/mPCL) blends were successfully prepared by sustainable electron-induced reactive processing (EIReP) without introducing any chemical compati...

The separation of toxic pollutants such as Pb2+, Cd2+, and Al3+ from water is a constant challenge as contamination of natural water bodies is increasing. Al3+ and especially Pb2+ and Cd2+ are ecotoxic and highly toxic for humans, even in ppb concentrations, and therefore removal below a dangerous level is demanding. Herein, the potential adsorber material starch, being ecofriendly, cheap, and abundantly available, was investigated. Thus, four different native starch samples (potato, corn, waxy corn, and wheat starch) and two oxidized starches (oxidized potato and corn starch) were comprehensively analyzed with streaming potential and charge density measurements, SEM-EDX, ATR-FTIR, 1H-NMR, and TGA. Subsequently, the starch samples were tested for the adsorption of Pb2+, Cd2+, and Al3+ from the respective sulfate salt solution. The adsorption process was analyzed by ICP-OES and SEM-EDX, and the adsorption isotherms were fitted comparing Langmuir, Sips, and Dubinin-Radushkevich models. Oxidized starch, for which chemical modification is one of the simplest, and also native potato starch were excellent natural adsorber materials for Al3+, Cd2+, and especially Pb2+ in the low concentration range, exhibiting maximum adsorption capacities of 84, 71, and 104 µmol/g for oxidized potato starch, respectively.

Biodegradable polylactide/masticated natural rubber (PLA/mNR) blends were prepared by electron induced reactive processing (EIReP) without using any chemical additives. The PLA/mNR blends showed droplet-matrix morphology with decreased mNR particle size after EIReP treatment. The absolute value of complex viscosity and storage modulus increased significantly for the EIReP modified blends, suggesting the improved melt strength and elasticity. The crystallization investigation showed that the cold crystallization peak of PLA phase gradually disappeared after EIReP modification. Instead, the crystallization peak arose during melt cooling process. Consequently, the crystallinity of PLA phase increased from 6.2% to 39.0% as the mNR content increased from 0 to 20 wt%. It was found that the softening temperature of PLA examined by dynamic mechanical analysis increased effectively with the characters of higher modulus compared to the non-modified blends. The EIReP modified blends exhibited excellent mechanical properties with 7-fold increase of impact toughness compared with neat PLA, implying a superior interfacial adhesion and chain interactions between the two polymer phases. Furthermore, the thermogravimetric analysis demonstrated that the thermal stability was slightly enhanced for the EIReP modified blends.

Polymer composite materials are used increasingly in material and engineering science. They provide outstanding mechanical and optical properties. The linkage between the polymer materials is crucial for achieving the desired properties. Understanding the linkage and structure of the polymer-polymer interface layer is a key for utilization polymer composite materials as well as for their fabrication. When analyzing the thin polymer-polymer interface it is important to achieve clear identification of molecular linker structures. One reliable analytical technique allowing this is surface enhanced Raman scattering (SERS) spectroscopy. This study aims at the in-situ evaluation of SERS spectra recorded from the Polycarbonate (PC) –Octadecylamine (ODA) interface to identify the formation of urethane bonds. The detailed analysis of SERS spectra taken before and after the chemical linkage reaction reveals the formation of urethane structures, indicating a chemical bond between PC and ODA. The spectral pattern of urethane groups was identified and evaluated by a reference Raman spectrum.

Malaria is still a major tropical disease, with Africa particularly burdened. It has been proposed that outdoor protection could aid substantially in reducing the malaria incidence rate in rural African communities. Recently, melt-spun polyolefin fibers containing mosquito repellents have been shown to be promising materials to this end. In this study, the incorporation of N,N‑Diethyl‑3‑methylbenzamide (DEET)—a popular and widely available mosquito repellent—in commercially available, amorphous poly(D,L-lactic acid) (PDLLA) is investigated with the aim of producing biodegradable mosquito-repelling filaments with a reduced environmental impact. It is shown to be possible to produce macroscopically stable PDLLA-DEET compounds containing up to 20 wt.-% DEET that can be melt-spun to produce filaments, albeit at relatively low take-up speeds. A critical DEET content allows for stress-induced crystallization during the spinning of the otherwise amorphous PDLLA, resulting in the formation of α-crystals. Although the mechanical integrity of the filaments is notably impacted by the incorporation of DEET, these filaments show potential as materials that can be used for Malaria vector control.

Electron induced reactive processing (EIReP) is an emerging technology for the development of high performance polymer materials. It simultaneously combines the traditional electron beam (EB) treatment of polymers and their melt mixing in the presence of shear stresses and/or rates of deformation. In comparison to traditional EB treatment of high-density polyethylene (HD-PE) at room temperature, EIReP modified HD-PE shows an inhomogeneous morphology, a self-nucleation effect as well as a significant increased tensile strength and decreased elongation at break. In order to identify the reason of these changed properties and the working principle of EIReP, HD-PE has been modified by EB treatment in solid and molten state as well as before and after the presence of shear stresses and/or rates of deformation. Shear stresses and/or rates of deformation were applied during injection moulding of tensile specimens. Based on results of previous work the EB treatments and EIReP of HD-PE were performed under nitrogen atmosphere in order to reduce oxygen induced side reactions. The process induced morphological and mechanical properties have been investigated using optical light microscopy, transmission electron microscopy as well as thermal analysis and tensile tests. Changes of molecular mass were measured with size exclusion chromatography and confirmed by rheological measurements. The results demonstrate that the morphology and specific tensile properties of HD-PE were only changed by an EB treatment before the influence of shear stresses and/or rates of deformation on EB modified HD-PE during injection moulding. In addition, the state of aggregate during EB treatment has no influence on morphology and tensile properties. Consequently, the EIReP induced effect based on electron induced changes of HD-PE molecular structure and the subsequent influence of shear stresses and/or rates of deformation.

Chitosan (flakes with a degree of deacetylation of 90%) was used as adsorbent for heavy metal ions in solution (copper, iron, nickel). The adsorption capacities were determined in dependence on the adsorption time and the initial metal salt concentration. With increasing adsorption time as well as the initial metal salt concentration the adsorption capacities increased. Highest adsorption capacity was achieved for copper(II)ions with 110 mg/L. Iron(II)- and nickel(II)ions adsorbed with an adsorption capacity of 80 mg/L. The surface of chitosan flakes were investigated before and after the adsorption process by SEM and SEM-EDX, respectively. The formation of crystal-like structures was observed by SEM analysis for the investigation of copper(II)sulfate and iron(II)sulfate. It has been noticed that iron(II)ions oxidized before the adsorption on chitosan occurs. In comparison, the adsorption of nickel salt resulted in a smooth layer on the chitosan surface. SEM-EDX analysis revealed that sulfate adsorbs on the chitosan surface besides the metal cations used.

This paper details a successful synthesis and comparison of a range of tri-metal hydrotalcite-like layered double hydroxides (LDHs) using urea hydrolysis. Transition-metal-substituted MgMAl-LDHs were synthesized with M = Fe, Co, Ni, Cu or Zn. 5 mol% and 10 mol% substitutions were performed, where Mg was substituted with Co, Ni, Cu and Zn, and Al with Fe. The successful synthesis of crystalline MgMAl-LDHs was confirmed using X-ray powder diffraction (XRD) analysis. Energy-dispersive X-ray (EDX) spectroscopy was used to identify substituted metals and determine changes in composition. Changes in morphology were studied using scanning electron microscopy (SEM). Thermogravimetric analysis was used to determine the effect of Fe-, Co-, Ni-, Cu- or Zn-substitution on the thermal degradation of the MgMAl-LDH phase. The structure, morphology and thermal behavior of the LDHs were shown to be influenced by the substituted transition metals. The observed thermal stability took the order MgNiAl- > MgFeAl- = MgAl- ≥ MgCoAl- > MgCuAl- > MgZnAl-LDH. The urea hydrolysis method was shown to be a simple preparation method for well-defined crystallite structures with large hexagonal platelets and good distribution of transition metal atoms in the substituted LDHs.

Specific physical and reactive compatibilization strategies are applied to enhance the interfacial adhesion and mechanical properties of heterogeneous polymer blends. Another pertinent challenge is the need of energy-intensive blending methods to blend high-tech polymers such as the blending of a pre-made hard polyurethane (-urea) with rubbers. We developed and investigated a reactive blending method to prepare the outstanding blends based on polyurethane-urea and rubbers at a low blending temperature and without any interfacial compatibilizing agent. In this study, the polyurethane-urea (PUU) was synthesized via the methylene diphenyl diisocyanate end-capped prepolymer and m-phenylene diamine based precursor route during blending at 100 &deg, C with polar (carboxylated nitrile rubber (XNBR) and chloroprene rubber (CR)) and non-polar (natural rubber (NR), styrene butadiene rubber (sSBR), and ethylene propylene butadiene rubber (EPDM)) rubbers. We found that the in situ PUU reinforces the tensile response at low strain region and the dynamic-mechanical response up to 150 &deg, C in the case of all used rubbers. Scanning electron microscopy reveals a stronger rubber/PUU interface, which promotes an effective stress transfer between the blend phases. Furthermore, energy filtered transmission electron microscopy (EFTEM) based elemental carbon map identifies an interphase region along the interface between the nitrile rubber and in situ PUU phases of this exemplary blend type.

High-density polyethylene (HD-PE) irradiated in the solid state is compared with HD-PE modified by electron-induced reactive processing (EIReP) which combines in a unique set-up the modification of polymers with high energy electrons and melt mixing processes. The effect of these different processes on the morphology and structural properties of HD-PE was investigated with X-ray analysis, differential scanning calorimetry, optical light microscopy combined with a hot stage and transmission electron microscopy as function of applied dose. The increased molecular mass was measured by using gel permeation chromatography and confirmed with rheological measurements. Even though the crystallinity and melting temperatures are constant within the studied range of dose significant differences have been observed in the morphology as well as in the crystallization behaviour. Electron treatment in the solid state causes a shift of crystallization temperature to lower temperatures due to branching and degradation whereas the irradiation under the dynamic conditions of melt mixing leads to higher crystallization temperatures with increased doses due to in-situ self-nucleation. The morphology and crystalline structure of HD-PE is not influenced by an electron treatment in the solid state, but by EIReP. Spatial and thermal stable heterogeneities have been generated only in HD-PE modified with high energy electrons under the dynamic conditions of melt mixing.

As a consequence of mining, heavy metal ions can be exposed to the environment hence contaminate ground water and surface water amongst others. The natural polymer chitosan was proved to be an excellent adsorber material for the effective removal of iron and sulfate ions in batch as well as in column experiments. The adsorption behavior of iron ions, as well as sulfate ions was investigated by utilizing chitosan flakes as a natural adsorbent. The removal was studied using adsorbance measurements, SEM and SEM-EDX. The adsorption capacity of chitosan was determined at different times. The received adsorption capacities for iron ions were very promising with a maximum adsorption capacity of 85 mg/g and a rate of separation of 100%. The maximum adsorption capacity obtained for sulfate ions was 188.8 mg/g and a rate of 80%.

Incorporation of precipitated silica rubber compounds is now a standard technology in energy efficient green tire manufacturing process. In the present work silica nanoparticles were generated by an in situ sol–gel technique in solution styrene butadiene rubber (SSBR) using tetraethylorthosilicate (TEOS) as silica precursor. A full control over the amount of silica and size of the silica particles is realized while maintaining a good distribution and dispersion level of the nanosilica particles. In the present case the amount of synthesized silica were varied from 10–50 phr (parts per hundred) and the particles size was found to remain in the range of 200–300 nm. The in situ silica based rubber composites offer better processing characteristics as compared with standard commercial precipitated silica at the same loading level. The reinforcing character of in situ silica was further enhanced by the use of a silane coupling agent, i.e. bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT). Various instrumental techniques, such as tensile test, dynamic mechanical analysis and strain sweep analysis, abrasion test, rebound test and Mooney viscometry reveal superior mechanical performance and good processability of the in situ silica composites. Scanning and transmission electron microscopy studies indicate that the particle size distribution remains in the same range irrespective of the concentration of the silica particles.

In this work we describe layered double hydroxide (LDH), known as naturally occurring hydrotalcite, based rubber composites that can serve as outstanding fire retardant elastomeric materials. The preparation and detailed characterization of these composites are presented in this study. The inherent slow sulfur cure nature of EPDM rubber is considerably improved by the addition of LDH as realised by the observation of a shortening of the vulcanization time and an improvement of ultimate rheometric torque. This behavior of LDH signifies not only the filler-like character of itself, but also offers vulcanization active surface properties of layered double hydroxide particles. A good rubber–filler interaction was also realised by observing a positive shift of the glass transition temperature of ethylene propylene diene rubber (EPDM) in dynamic mechanical analysis (DMA). The flame retardant property was studied by the cone calorimeter test. The cone calorimeter investigation with sulfur cured gum rubber compounds found a peak heat release rate (PHRR) value of 654 kW m−2. However, at a higher phr loading of Zn–Al LDH i.e., at 40 phr and 100 phr, the PHRR is diminished to 311 kW m−2 and 161 kW m−2, respectively. Thus, this present work can pave the way to fabricate environmentally friendly fire retardant elastomeric composites for various applications.

The study confirms the interaction of sulfate ions (SO42−) into the polymer chains of chitosan under acidic conditions. As a result the crystallinity of chitosan decreases with (1) increasing protonation of the amino groups and (2) increasing SO42− concentration. The adsorption of iron ions (Fe2+/3+) resulting from (FeSO4)aq onto the chitosan surface takes place incidentally by the oxidative effect of Fe2+/3+ with formation of orthorhombic α-FeOOH and γ-FeOOH. The separation of iron and sulfate ions correlates stoichiometrically. Chitosan with different degrees of deacetylation (DD) were used in order to investigate the influence of DD on the adsorption behavior of iron and sulfate ions. The higher the DD of chitosan, the more iron and sulfate ions can be adsorbed. Langmuir isotherms showed good agreement with the adsorption data obtained (qDD=90 %(Fe) = 2.36 mmol g-1; qDD=90 %(SO42−) = 2.58 mmol g-1). After adsorption process, the adsorber was analyzed extensively via X-ray diffraction, FTIR, 13C-NMR, SEM/EDX measurements and Mossbauer spectroscopy.

Composite microparticles of CaCO3 and two pectin samples (which differ by the functional group ratio) or corresponding nonstoichiometric polyelectrolyte complexes with different molar ratios (0.5, 0.9 and 1.2) are obtained, characterized and tested for loading and release of streptomycin and kanamycin sulphate. The synthesized carriers were characterized before and after drug loading in terms of morphology (by SEM using secondary electron and energy selective backscattered electron detectors), porosity (by water sorption isotherms) and elemental composition (by elemental mapping using energy dispersive X-ray and FTIR spectroscopy). The kinetics of the release mechanism from the microparticles was investigated using Higuchi and Korsmeyer–Peppas mathematical models.

The biodegradable polysaccharide chitosan possesses protonated and natural amino groups at medium pH values and has therefore been used as an adsorbing material for nickel salts in water treatment. Nickel is a problematic heavy metal ion which can cause various diseases and disorders in living organisms. Here, we show the influence of oxyanions (e.g., nitrate and sulfate) to the adsorption of nickel ions. Hence, simultaneously we are addressing the increasing global problem of nitrate and sulfate ion pollution in groundwater and surface water. A series of adsorption experiments was carried out in order to determine (i) the adsorption equilibrium, (ii) the adsorption capacity in dependence on the initial nickel ion concentration, and (iii) the influence of the anion presented in solution for the adsorption capacity. Surface morphology of chitosan flakes before and after the adsorption process has been studied with SEM-EDX analysis. The chitosan flakes exhibited promising adsorption capacities of 81.9 mg·g−1 and 21.2 mg·g−1 for nickel (sulfate) and nickel (nitrate), respectively. The calculated values of Gibbs free energy change ΔG0 confirm the higher adsorption of nickel ions in presence of sulfate ions. Hence, higher anion valence leads to a higher adsorption capacity.

Layered silicate-incorporated polyamide 6 (PA6) nanocomposites were studied to undertake correlations between morphological, rheological, permeability, and mechanical characteristics. The microstructure of nanocomposite specimens was seen through X-ray diffraction, atomic force microscopy, and transmission electron microscopy measurements. In addition, impact, tensile, and permeability data were analyzed combining the theoretical and experimental analyses to draw a convincing conclusion on the state of exfoliation and intercalation of layered silicates throughout the PA6 matrix. The results provided support for the fact that introduction of silicate nanofiller brings about some advantages like higher impact and modulus, at the same time some drawbacks arising from the improper dispersion of nanoplatelets. It was also revealed that microscopic studies do not necessarily agree with each other regarding filler dispersion state. The correlations between microstructure and experimental data from mechanical and permeability tests were checked by some well-established theoretical models. The trends in the test results were somewhat dependent on the state of filler dispersion. The role of the crystalline areas in achieving higher permeability resistance was also discussed, in a short review, to be comprehensively discussed in a future work. J. VINYL ADDIT. TECHNOL., 2015. © 2015 Society of Plastics Engineers

Graphene oxide (GO) filled poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HPF) copolymer nanocomposites as promising piezoelectric materials are developed, and their crystallization behavior and chain folding free energy are examined. Appropriate distribution of GO nanoparticles in the copolymer is confirmed by transmission electron microscopic analysis. The crystalline structure of nanocomposites is analyzed by wide-angle X-ray scattering and Fourier transform infrared spectroscopy. The results show an increase in the β-phase content of PVDF-HPF copolymer in the presence of GO. Non-isothermal crystallization kinetics of the neat polymer and corresponding nanocomposites are studied by a multiple heating rate differential scanning calorimetry using modified Avrami–Jeziorny and Liu models. Moreover, barrier energy of crystallization is calculated by Friedman and Kissinger models. It is found that addition of GO to the copolymer increases nucleation activity of the nanocomposites. Investigation on linear crystal growth via Hoffman's theorem indicates an enhanced nucleation activity upon increasing GO content. The surface folding free energy of the neat polymer is changed from 5.79 × 10−2 to 7.27 × 10−2 J m−2 upon addition of 5 wt% of GO. A bundle-like mechanism is proposed, which can explain the crystallite growth. Analysis based on Vyazovkin theorem reveals that the crystallization activation energy is independent of GO at elevated temperatures.