Pure Polymer Samples Research Articles

Corn pomace as a substitute for wood raw material in lignocellulosiccomposite technology

Corn pomace as a substitute for wood raw material in lignocellulosic composite technology. Composites made from polymers PE, PP, PLA and modified starch with addition of corn pomace were produced and subjected quality parameters test. There were examined such parameters as: density, static bending strenght and modulus of elasticity and also water absorption and thickness swelling after 2 h and 24 h soaking in water, wettability and surface roughness. In general, the addition of corn pomace to polymers caused changes of parameters and through comparing parameters of different composites and control samples it was possible to indicate corn composite variants that occurs to have similar properties to pure polymer samples. Waste products should be seriously considered as a valuable substitute of wood raw material, but characteristics of composites should be improved through further research.

Silicone-based materials with tailored MR relaxation characteristics for use in reduced coil visibility and in tissue-mimicking phantom design.

The development of materials with tailored signal intensity in MR imaging is critically important both for the reduction of signal from non-tissue hardware, as well as for the construction of tissue-mimicking phantoms. Silicone-based phantoms are becoming more popular due to their structural stability, stretchability, longer shelf life, and ease of handling, as well as for their application in dynamic imaging of physiology in motion. Moreover, silicone can be also used for the design of stretchable receive radio-frequency (RF) coils. Fabrication of materials with tailored signal intensity for MRI requires knowledge of precise T1 and T2 relaxation times of the materials used. In order to increase the range of possible relaxation times, silicone materials can be doped with gadolinium (Gd). In this work, we aim to systematically evaluate relaxation properties of Gd-doped silicone material at a broad range of Gd concentrations and at three clinically relevant magnetic field strengths (1.5 T, 3 T, and 7 T). We apply the findings for rendering silicone substrates of stretchable receive RF coils less visible in MRI. Moreover, we demonstrate early stage proof-of-concept applicability in tissue-mimicking phantom development. Ten samples of pure and Gd-doped Ecoflex silicone polymer samples were prepared with various Gd volume ratios ranging from 1:5000 to 1:10, and studied using 1.5T and 3T clinical and 7T preclinical scanners. T1 and T2 relaxation times of each sample were derived by fitting the data to Bloch signal intensity equations. A receive coil made from Gd-doped Ecoflex silicone polymer was fabricated and evaluated in vitro at 3T. With the addition of a Gd-based contrast agent, it is possible to significantly change T2 relaxation times of Ecoflex silicone polymer (from 213ms to 20ms at 1.5T; from 135ms to 17ms at 3T; and from 111.4ms to 17.2ms at 7T). T1 relaxation time is less affected by the introduction of the contrast agent (changes from 608ms to 579ms; from 802.5ms to 713ms at 3T; from 1276ms to 979ms at 7T). First results also indicate that liver, pancreas, and white matter tissues can potentially be closely mimicked using this phantom preparation technique. Gd-doping reduces the appearance of the silicone-based coil substrate during the MR scan by up to 81%. Gd-based contrast agents can be effectively used to create Ecoflex silicone polymer-based phantoms with tailored T2 relaxation properties. The relative low cost, ease of preparation, stretchability, mechanical stability, and long shelf life of Ecoflex silicone polymer all make it a good candidate for "MR invisible" coil development and bears promise for tissue-mimicking phantom development applicability.

Print parameter optimization and mechanical deformation analysis of alumina-nanoparticle doped photocurable nanocomposites fabricated using vat-photopolymerization based additive technology

As the recent trend of fabricating high-strength polymer has been gaining more attention in the market, researchers are exploring the possibility of using a 3D printing technique for the same. Vat-photopolymerization additive technology has good process capability and produces high-quality photopolymer parts with greater geometrical complexity. This paper proposes the vat-photopolymerization process to fabricate high-strength acrylate-based photopolymer composite with improved mechanical strength. The composite structures contain 1.0, 2.0, and 3.0 wt percentages of 13 nm average-sized alumina (Al2O3) nanoparticle (NP) as the reinforcement and acrylate photopolymer as matrix material. The viscosities of all the prepared suspensions were measured to determine the printing properties of the prepared nanocomposites, and these values are within the feasible printing limit. Furthermore, the depth of cure and time of exposure to UV light were optimized to achieve the desired level of printing performance. The thermogravimetric analysis (TGA) of the alumina nanocomposites reveals that the addition of alumina NP has minimal influence on the thermal stability of the photopolymer matrix. To ascertain the mechanical strength of the 3D printed products, tensile tests are performed, and it was witnessed that 1.0% weight fraction of alumina-NP loaded specimen experienced the highest tensile strength amongst all the weight fractions of alumina-NP considered, and its value increased by ∼48% when compared against the pure acrylate polymer sample. The increase in strength values for the alumina-NP loaded specimen was explained using dynamic mechanical analysis and optical and scanning electron micrographs. A constitutive elastic-viscoplastic isothermal non-linear time-dependent material model is also developed to predict the post-yield strain-softening behavior of these nanocomposites. The weight fraction and optimal weight fraction of alumina nanoparticles are correlated using semi-empirical equations of various model parameters.

Effect of coir fiber and TiC nanoparticles on basalt fiber reinforced epoxy hybrid composites: physico–mechanical characteristics

In the present study, the effect of coir fiber and titanium carbide (TiC) nanoparticles on physico-mechanical and thermal characteristics of basalt fiber reinforced bio/ synthetic epoxy hybrid composites were investigated. Two types of composites were prepared using bio epoxy Sr 33 and synthetic epoxy YD-535 LV, the similar fabrication method, the same volume fractions, static stiffness, and comparable densities. The flexural, tensile, impact, porosity, water absorption tests were carried out, and the tensile fracture condition examined. Analytical methods, such as FTIR, SEM, and TGA, have been conducted to study the structures' modification. Results from this investigation signified that the addition of coir fiber and TiC nanoparticles showed a significant enhancement in mechanical and thermal characteristics with the effect of the highest load transfer between the fillers and matrix materials. The newly developed epoxy hybrid composites have higher resistance from a change in temperature than the pure polymer sample, as evident from thermal stability analysis.

Pyrolysis of Mixed Plastic Waste: I. Kinetic Study.

Plastic wastes have become one of the biggest global environmental issues and thus recycling such massive quantities is targeted. Low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS) are considered among the main types of plastic wastes. Since pyrolysis is one of the most promising recycling techniques, this work aims to build knowledge on the co-pyrolysis of mixed polymers using two model-fitting (Criado and Coats–Redfern) methods. Seventeen co-pyrolysis tests using a thermogravimetric analyzer (TGA) at 60 K/min for different mixed compositions of LDPE, HDPE, PP, and PS were conducted. It was observed that the pyrolysis of the pure polymer samples occurs at different temperature ranges in the following order: PS < PP < LDPE < HDPE. However, compared to pure polymer samples, the co-pyrolysis of all-polymer mixtures was delayed. In addition, the synergistic effect on the co-pyrolysis of polymer blends was reported. The Master plot of the Criado model was used to determine the most suitable reaction mechanism. Then, the Coats–Redfern model was used to efficiently obtain the kinetic parameters (R2 ≥ 97.83%) and the obtained values of the activation energy of different polymer blends were ranging from 104 to 260 kJ/mol. Furthermore, the most controlling reaction mechanisms were in the following orders: First order reaction (F1), Contracting sphere (R3), and then Contracting cylinder (R2).

Mechanical Properties and Electrical Conductivity of Poly(methyl methacrylate)/Multi-walled Carbon Nanotubes Composites

Carbon nanotubes (CNTs) remain one of the most efficient reinforcing material for enhanced mechanical and electrical properties. In this study, the effects of multi-walled CNTs (MWCNTs) fillers on mechanical, structural, and electrical properties of polymethyl methacrylate (PMMA)/MWCNTs composites were studied. The PMMA/MWCNTs composites, containing varying MWCNTs concentration of 0.1, 0.3, and 0.5 wt%, were prepared by a solution casting method. The mechanical properties of the composites such as tensile strength, elongation, Young modulus, tear resistance, fracture energy, impact strength, and hardness were investigated. Results showed that the mechanical properties of the composites were enhanced significantly. At 0.5 wt% MWCNTs, the tensile strength, elongation, tear strength, hardness, fracture energy and impact strength increased by 397%, 567%, 89%, 27%, 12%, and 36%, respectively, while the Young modulus decreased by 26% compared to pure PMMA polymer sample. Both the dc electrical conductivity and the activation energy increased with increased concentration of MWCNTs. From the electrical conductivity measurements, the percolation threshold was found to equal ~ 0.55 wt% MWCNTs. Based on the Fourier-transform infrared spectroscopy analysis, enhancement of mechanical and electrical properties is attributed to the formation of covalent bonds between polymer strands and MWCNTs. Moreover, a mechanism was proposed to describe the influence of MWCNTs on electrical and mechanical properties of PMMA/MWCNTs composites.

Enhanced Absorption Edge of Anchusa-Italica-Doped Pentacene towards Optoelectronic Applications

The dye-doped polymer is commonly used in the field of optoelectronics, given its effectiveness in optimising the device’s performance. This study is devoted to the synthesis and characterisation of Anchusa-Italica-doped Pentacene thin-film. Scanning electronic microscopy structural analysis, Fourier transform spectroscopy, and UV-visible transmittance spectra with a range of 300-900 nm were also carried out. The fundamental optical properties such as the absorption coefficient, optical energy gap, absorption and refractive indices were calculated based on the methods already used in the literature as Tauc’s relationship. The morphology of the samples indicated that dye structure was affected in the doped pentacene. The Fourier transform infrared technique (FT-IR) resulting spectrum of the doped samples also showed a significant absorption peak corresponding to C-H as an index of impurities. The calculated band-gap energy of the impurity sample was reduced and was the lowest compared to both the pure dye and polymer samples. The optical absorption and transmittance spectra revealed that it was positioned in the desirable ranges for optoelectronic applications. An anomaly in the absorption index was also observed through excitation of the resonance mode with transparent indication. This effect was deduced from the calculation of the refractive index. The results presented in this paper significantly contribute to the developments in the field of optoelectronic devices based on dye/polymer organic materials.

Optical and structural properties of drop-cast PVA/PEG polyblends

In the present study, the drop cast films of polyvinyl alcohol (PVA), polyethylene glycol (PEG) and optimized PVA:PEG (50:50) polyblend were studied. The pure polymer and polyblends samples were characterised by using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Optical Absorption Spectroscopic Techniques. Changes in the morphology of optimized PVA:PEG polyblend has been observed in SEM photographs. FTIR results have been observed to form H-bond between PVA and PEG which confirms the plasticizing effect of PEG on PVA. The absorption maxima is observed at 325 nm and 300 nm for the pure PEG and PVA samples, while it is found to shift to 320 nm for the polyblends. The shift in peak related to absorption edge may attribute to the change in polymeric chain mobility as well as crystallization behaviour during the blending process. The value of indirect optical gap is found to be 1.75 eV, which very less as compared to the pure components. An increase in the value of B−1 has been observed indicating an enhancement of disorder with the formation of polyblends. These results are very important for realizing their applications as optical components.

Why not stir casting for polymer composites? Investigations on poly lactic acid based wood plastic composite

Poly Lactic Acid biopolymer was fabricated through four different methods namely Stir Casting, Injection moulding, Extrusion and compression moulding. The pure polymer sample was processed in these different methods to determine the impact of different processing methods on the mechanical property (tensile strength) of PLA. Tensile test was carried out to ASTM D628 standard for all the samples that were fabricated. The tensile strength of the samples that were fabricated through injection moulding, extrusion and compression moulding (named IPLA, EPLA and CPLA respectively) had very marginal difference between themselves while the one fabricated through stir casting method (named as SPLA) had a tensile strength reduced to one third of the value of the result that was obtained through the samples that were processed using the former methods. On conducting further experimentation with 20 wt% wood flour reinforcement into PLA to obtain a Wood Plastic Composite (WPC) and repeating the same processing and testing method, the tensile strength of the wood flour reinforced composites were found to increase in all the four cases of processing methods when compared to their plain polymer products correspondingly. Similar to the plain polymers the tensile strength of the composites also showed marginal difference between themselves in the Injection moulded, extruded and compression moulded methods while the stir casted composite surprisingly resulted in the same one third reduction in tensile strength that was seen on the plain polymers when compared with the former methods. The final verdict of the investigations is that stir casting method is effective and the cheapest processing method of all, the weight of the stir casted polymer and its composite was the lowest among all the processing methods respectively, the mechanical properties (especially tensile strength) of the stir casted polymer and its composite was exactly one third of the value that was obtained through the other regular processing methods that use pressure.

The synthesis of cyclic polymers by olefin metathesis: Achievements and challenges

ABSTRACTCyclic polymers have drawn considerable interest for their peculiar physical properties in comparison to linear polymers, despite their equivalent compositions. Synthetically, cyclic polymers can be accessed through either macrocyclic ring‐closure or by ring‐expansion polymerization, but the main challenge with either method is the production of highly pure cyclic polymer samples. This highlight describes advances in the area of cyclic polymer synthesis, with a particular focus on ring‐expansion metathesis polymerization. Methods for characterizing cyclic polymers and assessing their purity are also discussed in order to emphasize the need for additional robust and reliable methods for synthesizing and studying topologically complex macromolecules. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 228–242

Enhanced sound insulation and mechanical properties based on inorganic fillers/thermoplastic elastomer composites

In this work, a series of the thermoplastic elastomer (TPE) composites filled with micro CaCO3 and hollow glass microspheres (HGM) via alloying process were investigated. The plastic phase of TPE composite referred to polypropylene (PP) and the rubber phase was chosen by styrene butadiene styrene (SBS). SEM observation conformed that the inorganic particles were mainly dispersed in continuous PP phase and SBS phase remained in an isolated structure. The sound insulation property was measured by a four-microphone impedance tube. Compared to pure polymer sample, both CaCO3 and HGM-filled TPE composites exhibited greatly enhanced soundproof efficiency, which increased the sound transmission loss value from original 29 dB to 45 dB. The soundproof mechanism was investigated in detail. The damping of acoustic energy was contributed by the extended difference between the stiffness and acoustic impedance between plastic phase and rubber phase. The dispersion and property of inorganic fillers were considered as key factors to increase the dissipation of sound wave. Meanwhile, the mechanical properties of TPE composites were enhanced due to the addition of inorganic fillers.

The synthesis and study of the physicochemical and catalytic properties of composites with the sulfated perfluoropolymer/carbon nanofiber composition

Composites with the sulfated perfluoropolymer (SFP) (Nafion, etc.)—mesoporous support composition (SFP/support)—are promising solid acid catalysts with strong acid sites and very stable sulfo groups towards leaching processes. The effect of the SFP on the carbon nanofiber (CNF) (SFP/CNF) composite synthesis method, as well as the precursors of the acid phase, on the key acid catalyst characteristics (specific surface area and concentration and accessibility of the acid sites) is studied. The possibility of the direct composite synthesis from SO2F-polymer latexes obtained as a result of the water emulsion SFP synthesis (without the intermediate stages of isolating the SO3H form) is shown. The acid phase precursor types which are acceptable for the SFP/CNF composite synthesis (the equivalent polymer weight > 580 g/mol) are selected. The effect of the amount of the supported polymer on the total specific surface area and concentration and accessibility of the composite acid site is investigated. The structure of the synthesized composites is studied (by TEM, SAXS, and isopropanol TPD), and their catalytic activity in the test acetic acid esterification reaction is compared to the catalytic activity of pure polymer samples and acetic acid. It is found that the synthesized SFP/CNF samples outperform commercial SFP/SiO2 samples (SAC, DuPont), as well as the SFP/CNF samples prepared using polymer solutions in the SO3H form, in terms of the catalytic characteristics.

Structural, optical, and electrical characterization of chitosan: methylcellulose polymer blends based film

Solid polymer blend system based on chitosan (CH) and methylcellulose (MC) have been prepared through solvent casting technique and characterized by X-ray diffraction (XRD), UV–Visible, and impedance spectroscopy. The XRD data revealed the increase of amorphous domains of polymer blend matrix comparing to that of the pure polymers. The estimated optical band gap energy of CH:MC blends with 75:25 weight ratio showed a minimum value of 5.135 eV, companion with the maximum value of tail of localized state. Electrical conductivity analysis indicates that the blend samples have a larger conductivity compared to that of pure polymer samples. The highest room temperature dc conductivity was achieved for CH:MC blends with 75:25 weight ratio. Thus, the optical and electrical results confirm the same result. Temperature-dependence dc conductivity study follows Arrhenius model. The highest conducting composition has the lowest activation energy (0.46 eV). The frequency dependence of the ac conductivity follows Jonscher’s power law and indicates that the correlated barrier hopping is the most apposite mechanism for conduction in the present system. The asymmetric peak of the imaginary part of electric modulus obtained from the dielectric analysis suggests a non-Debye type relaxation.

Polarization reversal in organic-inorganic ferroelectric composites: Modeling and experiment

Tailoring of ferroelectric properties of copolymer P(VDF-TrFE) by incorporation of ceramic inclusions in the polymer matrix is promising for advanced applications in sensorics. We have observed experimentally that in composites of P(VDF-TrFE) with barium-doped lead zirconate titanate (BPZT), the remanent polarization increases, while the coercive field substantially decreases in comparison with the pure polymer samples. Results of simulation in framework of the modified Weiss model have shown that the changes of the hysteresis loops characteristics are due to increase of the dielectric susceptibility of the composite as compared to pure PVDF-TrFE. This originates from the strong dispersion of the mean field constant α, which describes the feedback of the polarization on the electric field at the location of the dipoles and is closely related with the local increase of composite susceptibility in the vicinity the BPZT inclusions. This phenomenon effectively becomes macro-scale due to the long-range nature of the inhomogeneous elastic and electric fields occurring at the interfaces between the matrix and inclusions.

Enhanced Energy Storage of Dielectric Nanocomposites at Elevated Temperatures

Enhancing the performance of dielectric capacitors toward higher energy density and higher operating temperatures has been drawing increased interest. Therefore, in this investigation, research efforts were dedicated to the fabrication and characterization of nanocomposites in order to enhance the energy density at both room temperature and elevated temperature. The dielectric capacitors are fabricated using nanocomposites composed of BaTiO nanoparticles with polyimide (PI) matrix aiming at combining the high relative dielectric permittivity of the ceramic filler and the high breakdown strength of the polymeric matrix. Dielectric energy storage performance is assessed for nanocomposites with volume fractions ranging from 0 to 20% under operating frequency from 20 Hz to 1 MHz and temperatures ranging from 20 to 120C. It is observed that with the increase of temperature, the capacitance increased while the energy density slightly decreased but significantly higher than pure polymer samples. The highest energy density was found for BaTiO/PI nanocomposites with 20% volume fraction, 9.63 J/cm at 20C and 6.79 J/cm at 120C. Overall, testing results indicate that using nanocomposites of BaTiO/PI as a dielectric component shows promise for implementation to preserve high energy density values up to temperatures of 120C.

Polyurethane/polylactide-based biomaterials combined with rat olfactory bulb-derived glial cells and adipose-derived mesenchymal stromal cells for neural regenerative medicine applications.

Research concerning the elaboration and application of biomaterial which may support the nerve tissue regeneration is currently one of the most promising directions. Biocompatible polymer devices are noteworthy group among the numerous types of potentially attractive biomaterials for regenerative medicine application. Polylactides and polyurethanes may be utilized for developing devices for supporting the nerve regeneration, like nerve guide conduits or bridges connecting the endings of broken nerve tracts. Moreover, the combination of these biomaterial devices with regenerative cell populations, like stem or precursor cells should significantly improve the final therapeutic effect. Therefore, the composition and structure of final device should support the proper adhesion and growth of cells destined for clinical application. In current research, the three polymer mats elaborated for connecting the broken nerve tracts, made from polylactide, polyurethane and their blend were evaluated both for physical properties and in vitro, using the olfactory-bulb glial cells and mesenchymal stem cells. The evaluation of Young's modulus, wettability and roughness of obtained materials showed the differences between analyzed samples. The analysis of cell adhesion, proliferation and morphology showed that the polyurethane-polylactide blend was the most neutral for cells in culture, while in the pure polymer samples there were significant alterations observed. Our results indicated that polyurethane-polylactide blend is an optimal composition for culturing and delivery of glial and mesenchymal stem cells.

Reactivity of Polyolefins toward Cumyloxy Radical: Yields and Regioselectivity of Hydrogen Atom Transfer

Hydrogen atom abstraction from a series of homopolymers by cumyloxy radicals is examined under solvent-free conditions at temperatures that are relevant to radical-mediated polymer modifications. Abstraction efficiency data acquired for the thermolysis of dicumyl peroxide (DCP) within pure polymer samples establish an order of reactivity: poly(butadiene) (PBD) > poly(ethylene oxide) (PEO) > poly(ethylene) (PE) > poly(propylene) (PP) > poly(isobutylene) (PIB). The regioselectivity of hydrogen transfer from PE, PP, and PIB is assessed by model hydrocarbon experiments involving nitroxyl trapping of the alkyl radicals generated from pentane, 2,4-dimethylpentane, and 2,2,4,4-tetramethylpentane, respectively. Taken together, abstraction efficiency and regioselectivity data are discussed in terms of enthalpic and entropic contributions to H atom transfer rates, with particular emphasis on steric hindrance imposed by methyl substituents on secondary positions within PP and PIB. The utility of polymer oxidizabilit...

Entropy dominated behaviors of confined polymer—nanoparticle composites

Stretched polymers will lose their possible configurations if they are mixed with nanoparticles or touch a hard wall, which leads to a strong depletion attraction responsible for the enrichment of nanoparticles near substrates. Moreover, it is found that there exists a sacrifice mechanism in confined pure polymer samples or polymer—nanoparticle mixtures, that part of the polymers, in order to reach a minimum free energy for the total system, are adsorbed on hard walls even though they lose their conformation. The current study provides a simple yet effective approach for the design of thin polymer composites.

Study of PDMS conformation in PDMS-based hybrid materials prepared by gamma irradiation

Polydimethylsiloxane-silicate based hybrid materials have recognized properties (high flexibility, low elastic modulus or high mechanical strength) for which there are a large number of applications in development, such as for the bioapplications field. The hybrids addressed in the present study were prepared by gamma irradiation of a mixture of polydimethylsiloxane (PDMS) with tetraethylorthosilicate (TEOS) and zirconium propoxide (PrZr) without addition of any solvent or other product. The materials are homogeneous, transparent, monolithic and flexible. The structure dependence on the PrZr content is addressed. A combination of X-ray diffraction (XRD) and Infrared Spectroscopy (IR) was used. The results reveal that the polymer in the hybrids prepared with PrZr, in a content≤5wt%, shows a structure similar to that in the irradiated pure polymer sample. In these samples the presence of ordered polymer regions is clearly found. For samples prepared with higher content of Zr almost no ordered polymer regions are observed. The addition of PrZr plays an important role on polymer conformation in these hybrid materials.

Sedimentation studies of single and bi-component polystyrene solutions in analytical ultracentrifugation by comparison of two analysis methods: effect of polymer concentration

Sedimentation analysis with interference detection optics was carried out for pure polymer as well as 1:1 polymer mixture samples as a function of polymer concentration in analytical ultracentrifuge. The data analysis was carried out using analysis programs of Sedfit and VelXLAI to elucidate the advantages and limitations of the analysis methods. The concentration dependency of the sedimentation coefficient was observed and the distributions became narrower on increasing the polymer concentration in both the methods. The peak sedimentation coefficients at different concentrations for both pure polymer as well as polymer mixture samples were same in both the methods though the sedimentation coefficients of the components in the mixture were slightly different from the sedimentation coefficient of the same component, when measured alone. The programs were observed to generate similar information in the case of pure polymer sample; however, in more complex polymer mixture sample, the Sedfit program was observed to have significant difference in the shape of the sedimentation coefficient distributions as well as in the amount of the components detected.