Search

• Degradation processes in polyolefin plaques initiated by applying non-ionizing or ionizing radiation have been compared. • Plaques were prepared by melt-mixing of polyolefin with particular natural stabilizer and with or without spin trap TTBNB. • Generated radicals and structure changes caused by degradation processes were characterized by ESR and IR, respectively. • Presence of spin trap TTBNB made possible catching short-living radicals in HDPE, that could not be detected previously. • Polymer dynamics related to T g affects reactivity of generated radicals and concentration of created oxidation products. We investigated degradation processes in polymer plaques made of polyolefin (HDPE or UHMWPE or COC) prepared by melt-mixing with or without phenolic stabilizer (natural α-tocopherol or synthetic Irganox®1010) and spin trapping agent (TTBNB; 2,4,6-Tri‑tert-butylnitrosobenzene). The degradation was initiated either by low-energy, non-ionizing radiation (wavelengths corresponding to terrestrial range of solar UV radiation) or high-energy, ionizing radiation (electrons accelerated at 1.5 MeV). The motivation for the study was our recent finding that some phenolic stabilizers exhibited a surprising pro-oxidant activity in polyolefins subjected to non-ionizing radiation. Consequently, we asked if the phenolic stabilizers in polyolefins behave in the same way during long-term, low-energy, non-ionizing UV irradiation and after short-term, high-energy, ionizing e-beam irradiation. All samples were characterized thoroughly by means of electron spin resonance (ESR; the information about radiation-induced radicals), infrared microspectroscopy (IR; the detection of oxidation products and structural changes), instrumented microindentation (MHI; local mechanical properties) and light and electron microscopy (LM and SEM; surface morphology). The results proved that (i) the degradation processes in polyolefins subjected to non-ionizing or ionizing radiation were different, (ii) the phenolic stabilizers exhibited mostly their expected antioxidant activity, while pro-oxidant activity was detected only for specific conditions and/or systems subjected to non-ionizing radiation, and (iii) the selected spin trapping agent, TTBNB, was stable enough to survive standard sample preparation by melt-mixing and catch short-living unstable radicals. [ABSTRACT FROM AUTHOR]

Polymer plaques made of high density polyethylene (HDPE) and of two types of cycloolefin copolymer (COC) differing in glass transition temperature, were stabilized with 0.2 or 1.0 wt % of natural (α-tocopherol) or synthetic (Irganox®1010) phenolic stabilizer or hindered amine stabilizer (Tinuvin®770) and aged using accelerated weathering technique (WOM). The efficiency of the phenolic stabilizers was compared among themselves and with well-established Tinuvin®770. Concentration profiles of radicals generated inside polymer plaques during WOM exposure were determined by ESRI, profiles of oxidation products and crystallinity inside the HDPE plaques were determined by IR microspectroscopy, oxidation products in COC copolymers were identified using ATR, the changes of local mechanical properties of the polymer plaques were characterized using microindentation hardness testing, and their morphology was studied by light and/or scanning electron microscopy. All the techniques evidenced high stability of neat COC against photooxidation processes, whereas neat HDPE exhibited fast photooxidation of the surface layers. Tinuvin®770 was found to provide long term protection to both HDPE and COC against photodegradation. In contrast, the same polymers stabilized with the natural phenolic antioxidant α-tocopherol (the most active component of vitamin E) or synthetic phenolic antioxidant Irganox®1010 exhibited an increase in the surface oxidation in comparison with the neat polymers during WOM exposure, proving prooxidant activity of phenolic stabilizers during WOM exposure in all polymers studied. The prooxidant activity α-tocopherol was stronger in comparison with Irganox®1010. We conclude that neither of the two phenolic stabilizers was able to provide long term protection of the investigated polymers against photooxidation. • Accelerated weathering of HDPE and COC polymers stabilized with phenolic stabilizer. • Prooxidation activity of 1% of α‑tocopherol or Irganox® 1010 during photooxidation. • Limited prooxidation activity at lower concentration of stabilizers (0.2 wt %). • The stabilizers do not protect the polymers subjected to photooxidation. [ABSTRACT FROM AUTHOR]

Abstract UV irradiation and thermal degradation were studied in marine conditions for styrene-butadiene rubber (SBR) and high density poly (ethylene) (HDPE) containing a Tinuvin® 770 hindered amine stabilizer. Electron spin resonance imaging (ESRI) was used to monitor degradation process in various depths and compare the polymers in terms of robustness to UV irradiation. In addition, both oxidative degradation and mechanical properties were studied by microscale methods, such as infrared microspectroscopy (IR) and microindentation hardness testing (MHI), enabling us to compare the material changes locally, i.e. both at the exposed surfaces and inside the samples. In SBR/Tin770 system, Tinuvin®770 stabilizer failed to protect the polymer matrix against photooxidation as clearly seen from IR/ATR spectra. The Weather-Ometer (WOM) aging resulted in strong oxidative degradation of both non-stabilized and stabilized SBR and caused remarkable changes in three regions of IR/ATR spectra. The strong photooxidative degradation was also manifested through the micromechanical properties of SBR/Tin770 systems. The change of the local properties was the same (within the standard deviations) for both stabilized and non-stabilized samples, which confirmed negligible stabilization efficiency of Tinuvin® 770 in the SBR system. In contrast to the SBR systems, similar experiments showed very dramatic stabilization effects in the HDPE/Tin770 system. ESR and 2D spectral-spatial ESRI directly proved the different degradation behavior of the two types of the composites: whereas in the SBR composites fast degradation was observed, high density poly (ethylene) showed much slower degradation. We attributed such striking difference to the modification of Tinuvin® 770 hindered amine stabilizer after vulcanization during preparation of SBR rubber, which apparently eliminated most of its protective activity. Highlights • Degradation of styrene-butadiene rubber (SBR) and high density polyethylene (HDPE) with Tinuvin® 770 stabilizer were studied. • In SBR/Tin770 system, Tinuvin®770 stabilizer failed to protect the polymer matrix against photooxidation. • In contrast to the SBR systems, similar experiments showed very dramatic stabilization effects in the HDPE/Tin770 system. • ESR and 2D spectral-spatial ESRI directly proved the different degradation behavior of the two types of the composites. • The difference is attributed to change of Tinuvin® 770 during SBR preparation, which limited most of its protective activity. [ABSTRACT FROM AUTHOR]

Blends of two biodegradable polymers, poly(lactic acid) (PLA) and poly(ϵ-caprolactone) (PCL), with strong synergistic improvement in mechanical performance were prepared by melt-mixing using the optimized composition (80/20) and the optimized preparation procedure (a melt-mixing followed by a compression molding) according to our previous study. Three different PLA polymers were employed, whose viscosity decreased in the following order: PLC ≈ PLA1 > PLA2 > PLA3. The blends with the highest viscosity matrix (PLA1/PCL) exhibited the smallest PCL particles (d∼0.6 μm), an elastic-plastic stable fracture (as determined from instrumented impact testing) and the strongest synergistic improvement in toughness (>16× with respect to pure PLA, exceeding even the toughness of pure PCL). According to the available literature, this was the highest toughness improvement in non-compatiblized PLA/PCL blends ever achieved. The decrease in the matrix viscosity resulted in an increase in the average PCL particle size and a dramatic decrease in the overall toughness: the completely stable fracture (for PLA1/PCL) changed to the stable fracture followed by unstable crack propagation (for PLA2/PCL) and finally to the completely brittle fracture (for PLA3/PCL). The stiffness of all blends remained at well acceptable level, slightly above the theoretical predictions based on the equivalent box model. Despite several previous studies, the results confirmed that PLA and PCL could behave as compatible polymers, but the final PLA/PCL toughness is extremely sensitive to the PCL particle size distribution, which is influenced by both processing conditions and PLA viscosity. PLA/PCL blends with high stiffness (due to PLA) and toughness (due to PCL) are very promising materials for medical applications, namely for the bone tissue engineering. [ABSTRACT FROM AUTHOR]

Photooxidation processes inside high-density polyethylene (HDPE) and cyclic olefin copolymer (COC) poly(ethylene- co -norbornene), both stabilized with biological antioxidant α-tocopherol (α-T-OH), has been investigated. Plaques made of the polymers stabilized with α-T-OH were subjected to long-term accelerated weathering in a Weather-Ometer (WOM). Concentration profiles of radicals generated in the plaques in dependence on WOM exposure time were determined by electron spin resonance imaging (ESRI). Concentration profiles of oxidation products and stabilizer, together with local crystallinity profiles inside the polymer plaques were determined by infrared (IR) microspectroscopy. The ESRI and IR profiles, supplemented by light microscopy (LM) and microindentation hardness measurements (MH), revealed the heterogeneity of the oxidation process and, surprisingly, the pro-oxidative activity of α-T-OH. Increasing concentration of products of polymer oxidation was found in the surface layers of the plaques stabilized with α-T-OH since the beginning of WOM treatment unlike the same control experiments with polymer plaques stabilized with HAS Tinuvin ® 770, where no oxidation products were observed after the same treatment before HAS depletion. We have confirmed that α-T-OH exhibits antioxidant activity during thermooxidation but it acts as a pro-oxidant agent during photooxidation. [ABSTRACT FROM AUTHOR]

Abstract: Morphology of polystyrene-block-poly(acrylic acid) vesicles was imaged by various modes of scanning electron microscopy (SEM), including recently developed wet scanning transmission electron microscopy (wet-STEM) by means of which we were able to follow the decrease in the thickness of a liquid solvent layer around the vesicles during controlled evaporation of water from the sample. Results show that wet-STEM allows for imaging of nanosized polymeric particles in the presence of the solvent. [Copyright &y& Elsevier]

• Accelerated weathering of HDPE and COC polymers stabilized with natural phenolic stabilizer (+)-catechin. • Results of IR microspectroscopy, ATR spectroscopy, ESRI, microindentation hardness testing (MHI), and light and/or scanning electron microscopy are in accordance with the conclusion that the natural phenolic stabilizer CAT exhibited pro-oxidant activity during accelerated photooxidation of both polymers and is not able protect the polymers against photooxidation. • At presence of TTBNB as the second additive adducts of polymer alkyl radicals generated in both polymers to TTBNB were detected. In this way TTBNB acted as processing stabilizer but no protective activity against photodegradation was connected with its presence. Polymer plaques made of high-density polyethylene (HDPE) or cycloolefin copolymer (COC) were stabilized with natural phenolic stabilizer (+)-catechin (CAT) and aged using accelerated weathering technique (WOM; accelerated photooxidation). The efficiency of the phenolic stabilizer was compared with a well-established hindered amine stabilizer (HAS) Tinuvin®770 (Tin770). In pursuit of the stabilization and identification of short-living radicals generated in the process of photooxidation of the polymers, a spin trapping agent 2,4,6-tri-tert-butylnitrosobenzene (TTBNB) was added to selected samples. Profiles of oxidation products and crystallinity inside the HDPE plaques were determined by IR microspectroscopy, oxidation products in COC copolymers were identified using ATR spectroscopy, concentration profiles of radicals generated inside polymer plaques during WOM exposure were determined by ESRI, the changes of local mechanical properties at the surface of polymer plaques were characterized using microindentation hardness testing (MHI), and the surface morphology changes were studied by light and/or scanning electron microscopy. All methods are in accordance with the conclusion that the natural phenolic stabilizer CAT exhibited pro-oxidant activity during accelerated photooxidation of both polymers, i.e. higher concentration of oxidation products, bigger changes of local mechanical properties and/or more microcracks on the exposed surfaces in comparison with non-stabilized systems and systems stabilized with Tin770. [ABSTRACT FROM AUTHOR]

• Amphiphilic copolymers with dendritic PE core and polyHEMA grafts prepared. • dPE-graft-PHEMA form 60–180 nm nanoparticles stable in water. • Self-assembly behavior is influenced by molar mass of copolymers. • Nanoparticles encapsulate hydrophobic Nile Red dye with up to 25% efficiency. By grafting from approach amphiphilic grafted copolymers with a hydrophobic core based on dendritic polyethylene and hydrophilic grafts of polyhydroxyethylmethacrylate (PHEMA) and polyhydroxypropylmethacrylate (PHPMA) were synthesized by tandem chain walking copolymerization and ATRP. Copolymers with molar mass 160–1400 kg/mol and ∼50–90% of hydrophilic grafts were obtained. Core-shell nanoparticles with very narrow size distribution were prepared from the copolymers by solvent displacement method. Particles diameter was efficiently regulated by molar mass of the copolymers in the range of 60–180 nm. We demonstrated that these nanoparticles can act as nanocontainers for hydrophobic Nile red dye, achieving up to 25% encapsulation efficiency. Dendritic polyethylene (dPE) nanoparticles with biocompatible polar PHEMA and PHPMA shell can find application in nanocatalysis and cargo delivery. [ABSTRACT FROM AUTHOR]

The monolayer form of CVD graphene is imposing crucial challenges in characterization of the targeted covalent functionalization due to the low amount of grafting moieties on the surface, which in turn hampers drawing conclusions about reactivity-properties relationships. Due to the growing interest in chemically modified graphene new, reliable and non-destructive methods for its characterization are critically required. Herein we demonstrate the use of surface-enhanced infrared absorption spectroscopy for detection of characteristic vibration modes of species being grafted to the material either via radical (Meerwein arylation) or nucleophilic substitution pathway on copper foil. The phenomenon is allowed by the appropriate metal surface morphology and no signal could have been obtained neither on Si/SiO 2 substrate, nor on bare copper. The surface of copper foil exhibit partial corrosion during the reaction which leads to the creation of active substrate for SEIRA. The measurements were performed using reflection-absorption and attenuated total reflection modes with almost identical results, thus making this analytical approach feasible, practical, non-destructive and easy to use for routine characterization of graphene functionalization. [ABSTRACT FROM AUTHOR]

Doubly filled nanocomposite poly(N-isopropylacrylamide)-SiO 2 -starch hydrogels were prepared via simultaneous polymerization of N-isopropylacrylamide (NIPAm) and tetramethoxysilane hydrolysis, in the presence of colloid amylopectin starch (4–30 wt.% in dry gel). Besides bulk hydrogels, also highly porous ones were prepared, the latter via solvent freezing during synthesis (cryogels). The branched starch molecules, which interpenetrate PNIPAm, appear to enforce less crosslinked but more regular PNIPAm network with a wider mesh, in place of the irregular one, which is normally obtained in divinyl-crosslinked PNIPAm. The hydroxyl groups of starch form efficient hydrogen bonds to the PNIPAm matrix, as well as to the SiO 2 nanofiller, which in turn also has strong H-bonds to PNIPAm. In bulk gels, a strong synergy of both fillers is clearly observed, leading to a marked increase in moduli, in spite of the wider network mesh. Very distinct is the improvement of tensile properties if starch is incorporated: the elongation at break increases 2 times in porous gels and 3–6 times in bulk ones. The gels’ toughness is also tremendously improved. The porous PNIPAm-SiO 2 -starch gels further display an ultra-fast swelling response to temperature jumps, both deswelling and re-swelling. Interestingly, starch-rich bulk PNIPAm-starch and PNIPAm-SiO 2 -starch gels also display a very fast (and also very extensive) temperature-induced deswelling, while their re-swelling is very slow (as would be expected). This behaviour practically represents a strong ‘one way response’ to temperature jumps. The specific properties of the interface between swollen PNIPAm and starch enable the rapid water escape from the bulk gels, especially if starch-rich domains are present. [ABSTRACT FROM AUTHOR]

This study aims at characterization of porous poly(ε-caprolactone) (PCL) scaffolds prepared by the methods of thermally induced phase separation (TIPS) and TIPS supported by particulate leaching (PL). Both techniques were combined with freeze-drying. Two PCL grades (with different average molecular weight characterized by MFR 6.1 and 1.2 g/10 min) were employed in the fabrication of scaffolds. Three types of salt (sodium chloride) particles were used in the TIPS-PL preparation of the PCL sample: (i) smaller particles (S) measuring 200–315 μm, (ii) larger particles (B) measuring 500–600 μm, and (iii) mixture of S and B particles (S/B = 1/1 wt/wt). The crystallization behavior of the PCL solutions and the thermal properties of scaffolds were investigated by polarized light microscopy (PLM) and differential scanning calorimetry (DSC), respectively. The structural changes of PCL were studied by attenuated total reflectance infrared spectroscopy (ATR-FTIR). The scaffold structure was visualized by means of scanning electron microscopy (SEM) and X-Ray micro-computed tomography (X-ray micro-CT). Furthermore, the density, porosity, water uptake, contact angle and compressive properties of scaffold were investigated. The molecular weight of PCL had an impact on the crystallization of the PCL solutions and thereby on the crystallinity of scaffolds and the morphology of pore walls formed during TIPS. Sodium chloride grains had an influence on the pore size and overall morphology of foam scaffolds prepared by TIPS-PL. The addition of NaCl decreased significantly the density and compressive properties and increased the porosity and water uptake of scaffolds. • Porous PCL scaffolds prepared by the methods of TIPS and TIPS-PL were compared. • The crystallization behaviour of the PCL solutions were investigated. • The crystallinity of scaffolds and the morphology of pore walls were described. • Structure-property relationships in PCL porous scaffolds were studied. [ABSTRACT FROM AUTHOR]

We report on the synthesis of poly(N-isopropyl acrylamide)- block -poly( n -butyl acrylate) (PNIPAm- b -PnBA) amphiphilic block copolymers and their temperature-responsive self-assembly behavior in aqueous solution. Well-defined PNIPAm- b -PnBA copolymers have been synthesized by a two-step RAFT polymerization scheme. The self-assembly behavior was studied by means of static and dynamic light scattering, 1 H NMR and fluorescence spectroscopy and transmission electron microscopy. The results show that already below the lower critical solution temperature (LCST) of PNIPAm, association of the PNIPAm blocks with hydrophobic dodecyl end groups of the charge transfer agent leads to the formation of loose aggregates of PNIPAm- b -PnBA micelles, the size and density of which increase with the increasing length of the PNIPAm block. The collapse of the PNIPAm blocks above the LCST leads to the decrease of the aggregates’ size and the increase of their density, but the collapsed PNIPAm chains do not allow for interpenetration of the micellar shells and no further aggregation occurs. [ABSTRACT FROM AUTHOR]

Abstract: Swelling and dynamic mechanical behavior in a broad frequency range of homogeneous and porous poly(2-hydroxyethyl methacrylate) gels were studied in relation to their matrix structure, gel morphology and nature of the swelling medium. Very lightly cross-linked gels showed up relatively large mechanical losses caused by slow relaxation of hydrophobic physical associates still proceeding at frequency 10−3 Hz. The macroporous gels of fused-spheres type morphology contained many dangling aggregates not bearing the stress which caused concentration of the stresses in the load bearing paths through the matrix. This is the reason for the sudden drop of storage modulus. In the α-relaxation region, the loss factors for homogeneous and porous gels merged into a single master curve. Reswelling of gels in a poor solvent caused a decrease of the swelling degree and shifted their α-relaxation to lower frequencies; reswelling in good solvent shifted the maximum of α-relaxation to higher frequencies. [Copyright &y& Elsevier]

Abstract: Fast thermoresponsive porous hydrogels based on the PNIPAM–silica nanocomposite were prepared and optimized in order to obtain increased force (pressure) response to temperature stimuli. This was achieved by increasing pore wall thickness via changing the monomers concentration during the hydrogels’ cryogenic synthesis. The mechanically strong and compact pore structure of the best gel made it possible to increase the force (pressure) response 3 times and the shear modulus 4 times, while the volume ratio of swollen to deswollen state remained unchanged, and the kinetics of the T-response was only moderately slower than in the case of the analogous ultra-fast responsive soft gels. The porous structure of the hydrogels (SEM), the dispersion and particle size of the nanofiller in the pore walls (TEM), as well as the swelling behavior and time-resolved force response to T-change are discussed in this work. [Copyright &y& Elsevier]

Abstract: The effect of polydispersity on dilute solution properties and microphase separation of polydisperse high-molecular-weight (M w >105 gmol−1) polystyrene-block-poly(styrene-co-acrylonitrile) diblock copolymers, PS-block-P(S-co-AN), was studied in this work. For experiments, a series of diblock copolymers with variable weight fractions of acrylonitrile units (w AN =0.08–0.29) and length of block P(S-co-AN) was synthesized using nitroxide-mediated radical polymerization (NMP) technique, namely, by chain extension of nitroxide-terminated polystyrene (PS-TEMPO). According to light scattering and viscometry measurements in dilute tetrahydrofuran (THF) solutions the studied diblock copolymers assumed random coil conformation with the values of characteristic structure factor R g/R h =1.50–1.76. It was found that polydisperse diblock copolymers being in strong segregation limit (SSL) self-assembled into microphase-separated ordered morphologies at ordinary temperature. The long periods of lamellar microdomains were larger compared to theoretical predictions for hypothetical monodisperse diblock copolymers. It was demonstrated by means of SAXS and TEM that a transition from a lamellar (LAM) to irregular face-centered-cubic (FCC) morphology occurred with increasing volume fraction of P(S-co-AN) block. [Copyright &y& Elsevier]

Poly(2-hydroxyethyl methacrylate) (PHEMA) crosslinked with ethylene dimethacrylate (EDMA) or N,O-dimethacryloylhydroxylamine (DMHA) was obtained in the form of slabs by bulk radical polymerization. Two porosity-inducing methods were investigated, phase separation using a low-molecular-weight porogen and a salt-leaching technique using NaCl and saccharose. Compared with the phase separation, the salt-leaching created open porous structures with voids of the size and shape of crystallites. To address its potentials in the context of stem cell therapies, undifferentiated mouse embryonic stem cells D3 (ES D3 cells) were seeded on the slabs and analyzed for the ability to grow on different types of non-degradable and/or degradable porous PHEMA hydrogels. The cells were able to proliferate only on PHEMA crosslinked with EDMA or 2 wt% DMHA. In order to assess the effect of gelatin, which is routinely used for ES cell cultures, PHEMA slabs were soaked in gelatin solutions and compared the number of cells on gelatin-treated and untreated slabs 4 days after cell seeding. Surprisingly, the number of cells was only slightly higher on gelatin-treated slabs. [Copyright &y& Elsevier]

[Display omitted] • Innovative polymer coatings on anodes improve electromediated biofilm eradication. • Coatings catalyze ROS generation or convert hydrophobic surfaces to bactericidal polycations. • Promising efficacy against Staphylococcus aureus biofilms demonstrated. • Addressing critical challenge in medical field: biofilm-associated infections. The formation of biofilm involves cell aggregation and adherence, enveloped by a self-produced extracellular matrix. In the medical domain, biofilm-associated infections pose significant challenges, especially concerning implants. This investigation focuses on enhancing electromediated bacterial biofilm eradication through polymer coatings on the anode. These coatings catalyze reactive oxygen species (ROS) generation or convert hydrophobic coatings to bactericidal hydrophilic polycations, detaching the biofilms that are predominantly polyanionic. The first approach employs a metallized polytetrathienylporphyrin layer with ROS catalytic capability, while the second involves an insoluble hydrophobic polyamide, which, upon oxidation, transforms into a bactericidal hydrolytically degradable polycation. Both approaches show promising efficacy in augmenting electromediated Staphylococcus aureus biofilm destruction. [ABSTRACT FROM AUTHOR]