Development of Pure Poly Vinyl Chloride (PVC) with Excellent 3D Printability and Macro- and Micro-Structural Properties

Unmodified polyvinyl chloride (PVC) has low thermal stability and high hardness. Therefore, using plasticizers as well as thermal stabilizers is inevitable, while it causes serious environmental and health issues. In this work, for the first time, pure food-grade PVC with potential biomedical applications is processed and 3D printed. Samples are successfully 3D printed using different printing parameters, including velocity, raster angle, nozzle diameter, and layer thickness, and their mechanical properties are investigated in compression, bending, and tension modes. Scanning electron microscopy is also used to evaluate the bonding and microstructure of the printed layers. Among the mentioned printing parameters, raster angle and printing velocity influence the mechanical properties significantly, whereas the layer thickness and nozzle diameter has a little effect. Images from scanning electron microscopy  also reveal that printing velocity greatly affects the final part's quality regarding defective voids and rasters’ bonding. The maximum tensile strength of 88.55 MPa is achieved, which implies the superiority of 3D-printed PVC mechanical properties compared to other commercial filaments. This study opens an avenue to additively manufacture PVC that is the second most-consumed polymer with cost-effective and high-strength features.     

4D Printing of Polyvinyl Chloride (PVC): A Detailed Analysis of Microstructure,Programming, and Shape Memory Performance

In this research, polyvinyl chloride (PVC) with excellent shape-memory effects is 4D printed via fused deposition modeling (FDM) technology. An experimental procedure for successful 3D printing of lab-made filament from PVC granules is introduced. Macro- and microstructural features of 3D printed PVC are investigated by means of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA) techniques. A promising shape-memory feature of PVC is hypothesized from the presence of small close imperfect thermodynamically stable crystallites as physical crosslinks, which are further reinforced by mesomorphs and possibly molecular entanglement. A detailed analysis of shape fixity and shape recovery performance of 3D printed PVC is carried out considering three programming scenarios of cold (T_g −45 °C), warm (T_g −15 °C), and hot (T_g +15 °C) and two load holding times of 0 s, and 600 s under three-point bending and compression modes. Extensive insightful discussions are presented, and in conclusion, shape-memory effects are promising,ranging from 83.24% to 100%. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state-of-the-art shape-memory materials library for 4D printing, and provide pertinent results that are instrumental in the 3D printing of shape-memory PVC-based structures.     

Investigation into the effect of carboxylic acid monomer on particle nucleation and growth in emulsifier-free emulsion copolymerization of styrene-butadiene-acrylic acid

Latexes of carboxylated styrene-butadiene rubber were prepared via batch emulsion copolymerization with different amounts of acrylic acid in the absence of emulsifier. The effect of acid monomer was investigated in the particle formation and growth. It was observed that the amount of acrylic acid strongly affected the particle formation. The number of particles and thus polymerization rate increased with increasing of the acid content. There was no significant difference in the polymerization rate per particle in all experiments. The results show that in this case particle growth process is less dependent on the acrylic acid amount in comparison with its influence on nucleation stage and then particle number. Several parameters such as polymerization rate and number of latex particle per unit volume of the aqueous phase were calculated. Attempt was made to evaluate the average number of growing chain per particle. Also average particle diameter of the above carboxylated SBR latexes was obtained through some calculations from the direct measurement of average particle diameter in the swollen state by light scattering technique for the first time.     

Thermal,mechanical, and barrier properties of polyethylene/surlyn/organoclay nanocomposites blown films prepared by different mixing methods

(Low‐density polyethylene) (LDPE)/clay nanocomposites were prepared by melt blending in a twin‐screw extruder by using different mixing methods. Zinc‐neutralized carboxylate ionomer was used as a compatibilizer. Blown films of the nanocomposites were then prepared. The effect of mixing method on the clay dispersion and properties of the nanocomposites was evaluated by wide‐angle X‐ray diffraction analysis, mechanical properties, thermal properties, and barrier properties. The structure and properties of nanocomposites containing different amounts of nanoclay prepared by selected mixing techniques were also investigated. It was found that melt compounding of Surlyn/clay masterbatch with pure LDPE and Surlyn (two‐step‐a method) results in better dispersion and intercalation of the nanofillers than melt mixing of LDPE/Surlyn/clay masterbatch with pure LDPE and surlyn (two‐step‐b method) and direct mixing of LDPE with clay. The films containing ionomer have good barrier properties. A wide‐angle X‐ray diffraction pattern indicates that intercalation of polymer chains into the clay galleries decreases by increasing the clay content. Barrier properties and tensile modulus of the films were improved by increasing the clay content. In addition, tensile strength increased in the machine direction, but it decreased in the transverse direction by increasing the clay content. DSC results showed that increasing the clay content does not show significant change in the melting and crystallization temperatures. The results of thermogravimetric analysis showed that the thermal stability of the nanocomposites decreased by increasing the clay content more than 1 wt%. J. VINYL ADDIT. TECHNOL., 21:60–69, 2015. © 2014 Society of Plastics Engineers     

Experimental investigation of continuous conductivity measurements during emulsion polymerizations having unstable/high‐fouling reaction mixture

Conductimetry is one of the online monitoring techniques employed for emulsion polymerization reactions, which can give continuous information about nucleation and growth of particles. The most important factor affecting conductivity sensors performance especially contacting (resistance) types is fouling. To investigate the consequences of fouling, four monomers with different tendencies for fouling were selected: methyl methacrylate, butyl acrylate, styrene, and butadiene. Two types of conductivity sensors were also selected to continuously measure conductivity: a two‐electrode sensor and an inductive sensor, and the performance of these sensors were evaluated based on some criteria such as conductivity behavior, amount of fluctuation, change in cell constant, repeatability, and status of the minimum of conductivity. The results obtained from the contacting sensor showed that fouling significantly decreased the performance of this sensor in different ways even in reaction mixtures having moderate fouling rates. However, the inductive conductivity sensor provided the possibility of reliably measuring conductivity during very high‐fouling and highly unstable emulsion polymerizations with very good repeatability. The capabilities of this sensor also allowed an exact recognition of the important points in the conductivity curves particularly the minimum of conductivity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44446.     

A computational study of adsorption H2S gas on the surface of the pristine,Al&P-doped armchair and zigzag BNNTs

Density function theory is used to study the H₂S adsorption on the surface of pristine, Al-, P- and Al&P- doped (4, 4) armchair and (8, 0) zigzag BNNTs. All considered different models for H₂S adsorption on the exterior and interior surface of nanotube are optimized by using B3LYP/6-31G (d, P) level of theory. The adsorption energy values (E_ads) of the B-I, B-II,C-I, D-I, D-II, F-I, F-II and H-II models are negative, while the E_ads values for the A-III, B-III, C-III, D-III, E-III, F-III, G-III and H-III models are positive. On the other hand, Al, P and Al&P doped in all models increase significantly the adsorption energy of H₂S on the surface of BNNTs, and so the selectivity of nanotube for adsorbing and making a sensor of H₂S increase significantly from original state. The positive values of the charge transfer parameters (ΔN) and more values of the electronic chemical potentials of H₂S gas for all studied models demonstrate that H₂S gas in this system has a donor electron effect on the nanotube. The MEP results display that a low charge transfer occurs from H₂S gas toward nanotube, resulting in a weak ionic bonding in the BNNTs’ surface.     

Preparation and characterization of a novel gelatin–poly(vinyl alcohol) hydrogel film loaded with Zataria multiflora essential oil for antibacterial–antioxidant wound‐dressing applications

This study was performed to evaluate the properties of poly(vinyl alcohol) (PVA), gelatin, and PVA–gelatin dispersions and films enriched with Zataria multiflora essential oil (ZO). The results reveal that the ζ potential, particle size, and viscosity values and the antioxidant and antibacterial activities of the dispersions changed significantly with the addition of ZO to the polymer matrix. Changes in the properties of the dispersions suggested the presence of interactions between PVA or gelatin and ZO. Such interactions could affect the mechanical and water‐barrier properties of the films. ZO induced remarkable decreases in the tensile strength, elastic modulus, and swelling and increases in the elongation at break, solubility, and water‐vapor permeability of the films. Scanning electron microscopy analyses proved the impact of ZO on the film morphology, which affected the film properties, including the mechanical and water‐barrier properties. The addition of ZO to the polymer led to a coarse film microstructure because of the hydrophobic ZO aggregates, which produced discontinuities in the film matrix. ZO considerably increased the antioxidant and antibacterial activities of the dispersions. Pseudomonas aeruginosa was the most resistant bacteria. The improved antioxidant and antimicrobial activities of the PVA–ZO and gelatin–ZO indicated that such products could effectively be used as wound dressings. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45351.     

Effect of support layer on gas permeation properties of composite polymeric membranes

PES/Pebax and PEI/Pebax composite membranes were prepared by coating the porous PES and PEI substrate membranes with Pebax-1657. The morphology and performance of the prepared membranes were investigated by SEM and CO₂ and CH₄ permeation tests. The CO₂ permeances of 28 and 52 GPU were achieved for PES/Pebax and PEI/Pebax composite membranes, respectively, with CO₂/CH₄ selectivities almost equal to that of Pebax (26). The experimental data were further subjected to a theoretical analysis using the resistance model. It was found that the porosity and the thickness of the dense section of PES substrate were an order of magnitude higher than those of PEI substitute. The porosity/thickness ratio of PEI substrate was, however, higher than PES, explaining the higher permeance of PEI/Pebax composite membrane. Substrates with porosities much higher than the Henis-Tripodi gas separation membrane were used in this work, aiming to achieve the selectivity of Pebax, rather than those of the substrate membrane materials.