Acetal Homopolymer Research Articles

Glucose-stabilized polyvinyl acetate homopolymer-based wood adhesive: synthesis and characterization

The purpose of this work was to study the synthesis and characterization of an adhesive based on a glucose stabilized polyvinyl acetate homopolymer. Vinyl acetate monomer was stabilised onto liquid glucose using emulsion polymerization, and polymerization happened using potassium persulfate as an initiator. Here, the effects of adding liquid glucose as a stabiliser for adhesives were studied. Therefore, the current research examines whether liquid glucose, introduced at weight-based concentrations of 0.5% and 1.0%, is suitable as a colloid to produce PVAc adhesives for wood. By measuring viscosity, pH, contact angle, differential scanning calorimetry (DSC), and the pencil hardness test of films, the effect of adding liquid glucose as a colloid on physical, thermal, and mechanical properties was investigated. The shear strength of the PVAc homopolymers applied to wood using emulsions with varied liquid glucose concentrations was measured using a universal tensile machine. As the concentration of liquid glucose increased, the viscosity of the adhesives also considerably increased. Water resistance significantly rose when liquid glucose content increased, as was found by measuring the water contact angle. The use of liquid glucose increased the hardness of PVAc films, which was supported by the glass transition temperature. According to EN 204-205, the tensile shear strength with 1.0% of liquid glucose increased by 63.88% and 45.67%, respectively, over a pristine sample after 6 h of bonding in a dry environment and 24 h in a wet environment. The study’s overall conclusion highlights the higher adhesion capability of PVAc emulsion-based adhesives stabilized by liquid glucose.

DuPont to sell Delrin acetal homopolymer unit to private equity firm

DuPont to sell Delrin acetal homopolymer unit to private equity firm

Development of process of ultrasonic pressing of the polyoxymethylene inserts for car anti-roll bars

The process of ultrasonic pressing of inserts made of high-viscosity acetal homopolymer (polyoxymethylene) in the production of anti-roll bar racks is considered. Some dependencies between ultrasonic pressure parameters are detected.

Effect of redispersible polymer powders on selected mechanical properties of thin-bed cementitious mortars

Modern mortars are complex multi-component systems. Among the mortar components, redispersible polymer powders (RDPs) play a unique role. They improve the rheology of fresh mortar while providing flexibility and tensile strength after it has hardened. The impact of polymeric binders on mortar properties has been and is currently the subject of intensive research. This paper describes how the use of different redispersible polymer powders affects cement mortars’ selected properties, i.e., crack bridging ability, adhesion determined by measurement of tensile strength and transverse deformation. Results show that all of the RDPs tested positively affect the properties of the examined system. The most significant increase in the mortar’s tensile adhesion strength was observed for the system with vinyl acetate homopolymer, the lower one for the systems with styrene-acrylic heteropolymers and vinyl acetate and ethylene heteropolymers. All tested redispersible polymer powders in the considered system increase the ability to bridge cracks in cement mortar. However, the smallest increment is observed for the acrylic homopolymer and styrene-butadiene heteropolymer. Other RDPs similarly increase the mortar’s cracks bridging ability under test defined as the ability of the hardened material (mortar) to stop the spread of cracks without damaging it. The results obtained for thin-bed cement mortars in terms of crack bridging ability were evaluated comparing the requirements for water-impermeable products. All examined RDPs showed a similar effect on the transverse deformation value of cement mortar.

Prediction of surface quality and optimization of process parameters in drilling of Delrin using neural network

The high-temperature polymers like Acetal homopolymer (Delrin) currently have a wide variety of use. They are quite often utilized in traditional components to reduce weight, cost or meet a specific application requirement, and so on. Some of preferred uses of such polymers include aircraft interiors, wire insulation, wire couplings and fixtures, and so on, particularly at high-temperature applications. The machining process like drilling may affect the near net shape of the final product. This experimental study is done through modeling and optimization for identifying the suitable tool and optimum parameters for drilling of Delrin polymer under dry conditions to achieve high surface finish. The three levels of parameters such as spindle speed ( N), feed rate ( f), and tool point angle ( Θ) are taken as control parameters of the response variable. Two different commercially available tool materials namely high-speed steel drill tool and solid carbide tool are accounted in experiments. L27 orthogonal array is initially taken for the experimentation in CNC turning center with horizontal drilling setup. Artificial neural network is employed to sample, train, and test the input parameters in order to lessen the experimental error and measurement error of response variables. Response surface models are developed and optimal parameters toward the surface quality of the hole are determined through the desirability function approach. It is found that the surface generated under dry mode with speed of 1026 r/min, feed of 0.1 mm/min, point angle of 118° recorded the surface roughness of 0.699 µm, which is considered to be the best for drilling Delrin material.

Superhydrophobic EVA copolymer fibers: the impact of chemical composition on wettability and photophysical properties

Fibers of poly(vinyl acetate) (PVAc) homopolymer and ethylene vinyl acetate (EVA) copolymers with varying vinyl acetate (VAc) contents between 25 and 40 wt.% have been prepared to investigate wettability and photophysical properties. At lower VAc contents, it was difficult to prepare fibers without any beads due to the presence of crystalline ethylene groups at higher concentrations. EVA copolymer composition strongly affected the wettability of fibers; all EVA copolymer fibers exhibited superhydrophobic behavior and CA values varied between 150° and 160° depending on copolymer composition while hydrophilic PVAc homopolymer fibers exhibited hydrophobic behavior with a CA of 134°. Photophysical properties of PVAc homopolymer and EVA copolymers were evaluated in terms of transmittance and emission intensity. Emission intensity and transparency of EVA copolymers were decreased with the increase of VAc contents due to its amorphous behavior.

Enhanced Multi-Objective Teaching-Learning-Based Optimization for Machining of Delrin

This paper deals with the optimization of machining parameters of speed, feed rate, and depth of cut that aim to simultaneously achieve the low surface roughness (SR) and high material removal rate (MRR) of a version of ACETAL homopolymer material known as Delrin. First, an L27 orthogonal array with three-level of cutting speed ( $V_{c}$ ), feed rate ( $f$ ), and depth of cut (ap) is formulated, and the experiments are conducted accordingly in a CNC turning machine using cemented carbide tool with insert angle of 80°. A response surface model is rendered from these experimental results, and two objective functions representing the SR and MRR of Delrin are derived. An enhanced multi-objective teaching–learning-based optimization (EMOTLBO) is then proposed to solve the multi-objective machining problem, aiming to minimize the SR and maximize the MRR of Delrin simultaneously. A fuzzy decision maker is also integrated to softly select the preferred solution from Pareto-front based on the importance level of both objective functions. Extensive simulation studies prove that EMOTLBO is more competitive than other existing algorithms for being able to produce a more uniformly distributed Pareto-front. Simulation results are further validated Experimentally, and the difference of lower than 5% is observed that imply to good agreement between the simulation and experimental results.

Long-Term Performance of Electrodes Based on Vinyl Acetate Homo-Polymer Binder

In this work we propose the use of a hydro-dispersible polymer such as the poly vinyl acetate as a binder for the production of electrodes for lithium-ion batteries. To increase the film forming properties of the polymer the poly vinyl was added with triacetin that acts as a plasticizer. The electrochemical stability of the polymer was tested by a polarizing electrode, formed by mixing the polymer with carbon. Subsequently, an electrode tape was prepared by using LiNi0.5Mn1.5O4 as the active material and characterized by SEM, EDS and TGA. Lithium metal cells were assembled and tested to evaluate specific capacity, power and energy density at various discharge rates. The cycle life of the cell was evaluated by galvanostatic charge/discharge cycles. The tests showed that the electrodes prepared with PVA plasticized with triacetin have very good electrochemical performance in terms of capacity retention as a function of the discharge rate and the cycle number. Our work demonstrates that the use of triacetin to plasticize the PVA allows to increase the electrochemical stability of the electrode likely due to an improvement of the slurry filmability. The proposed method could represent a promising technology for the production of long-term performance lithium batteries.

Hansen solubility parameter: from polyethylene and poly(vinyl acetate) homopolymers to ethylene–vinyl acetate copolymers

AbstractThe Hansen solubility parameters (HSPs) of two ethylene–vinyl acetate (EVA) copolymers (with 18 and 33 wt% of vinyl acetate) and their corresponding homopolymers (polyethylene, PE, and poly(vinyl acetate), PVAc) have been studied at various temperatures, employing the previously obtained Flory–Huggins parameters. From these latter values, a procedure based on the Hansen solubility spheres theory was employed to determine the HSPs, as well as the radius of interaction. The procedure was validated with literature data, with deviations of around 3%. The HSP values (dispersion, polar and association terms, respectively, all in MPa1/2) at 333.15 K are 14.84, −3.88 and 1.78 for PE, 17.65, −1.24 and 2.76 for EVA410 (with 18 wt% of vinyl acetate), 17.52, 0.15 and 3.61 for EVA460 (with 33 wt% of vinyl acetate) and 19.45, 10.59 and 5.76 for PVAc. The main characteristic of the obtained HSP values is that the high polar term of PVAc tends to increase the solubility character of the pure PE, and thus the EVA copolymers, allowing them to solubilize dispersion and polar compounds. Finally, it was also demonstrated that it is possible to predict the HSPs of EVA copolymers using the vinyl acetate content and the HSPs of pure PE and PVAc as input data. © 2017 Society of Chemical Industry

Development of a prototype chest digital tomosynthesis (CDT) R/F system with fast image reconstruction using graphics processing unit (GPU) programming

Digital tomosynthesis offers the advantage of low radiation doses compared to conventional computed tomography (CT) by utilizing small numbers of projections (~80) acquired over a limited angular range. It produces 3D volumetric data, although there are artifacts due to incomplete sampling. Based upon these characteristics, we developed a prototype digital tomosynthesis R/F system for applications in chest imaging. Our prototype chest digital tomosynthesis (CDT) R/F system contains an X-ray tube with high power R/F pulse generator, flat-panel detector, R/F table, electromechanical radiographic subsystems including a precise motor controller, and a reconstruction server. For image reconstruction, users select between analytic and iterative reconstruction methods. Our reconstructed images of Catphan700 and LUNGMAN phantoms clearly and rapidly described the internal structures of phantoms using graphics processing unit (GPU) programming. Contrast-to-noise ratio (CNR) values of the CTP682 module of Catphan700 were higher in images using a simultaneous algebraic reconstruction technique (SART) than in those using filtered back-projection (FBP) for all materials by factors of 2.60, 3.78, 5.50, 2.30, 3.70, and 2.52 for air, lung foam, low density polyethylene (LDPE), Delrin® (acetal homopolymer resin), bone 50% (hydroxyapatite), and Teflon, respectively. Total elapsed times for producing 3D volume were 2.92s and 86.29s on average for FBP and SART (20 iterations), respectively. The times required for reconstruction were clinically feasible. Moreover, the total radiation dose from our system (5.68mGy) was lower than that of conventional chest CT scan. Consequently, our prototype tomosynthesis R/F system represents an important advance in digital tomosynthesis applications.

Size-Effect Law for Scratch Tests of Axisymmetric Shape

AbstractThis paper presents a theoretical and experimental framework for the application of size-effect analysis to microscratch testing as a means to quantify the fracture properties and internal friction of materials at the microscale. The energetic size-effect law (SEL) for microscratch tests is developed for a general monomeric probe shape in terms of an intrinsic size function. The fundamental idea of the proposed approach is to rescale the scratch response to that of the flat punch, a conjecture that allows one to compare the SEL for different probe geometries, and thus solve for the asymptotic fracture toughness and effective process zone length from scratch tests done on homogenous (acetal homopolymer resin and polycarbonate resin) and inhomogeneous materials (mica ceramic and gas shale). As a material of current interest for controlled fracture studies, two samples of gas shale cored from the Marcellus and Eagle Ford formations are tested and analyzed to quantify all material properties that may ...

Adaptation of the cortical somatosensory evoked potential following pulsed pneumatic stimulation of the lower face in adults

Cortical adaptation to sustained sensory input is a pervasive form of short-term plasticity in neurological systems. Its role in sensory perception in health and disease, or predicting long-term plastic changes resulting from sensory training offers insight into the mechanisms of somatosensory and sensorimotor processing.A 4-channel electroencephalography (EEG) recording montage was placed bilaterally (C3-P3, C4-P4, F7-P3, F8-P4) to characterize the short-term effects of pulsed pneumatic orofacial stimulation on the cortical somatosensory evoked potential (cSEP) in twenty neurotypical adults (mean age=21±2.88 years). A servo-controlled pneumatic amplifier was used to deliver a repetitive series of pneumatic pulse trains (six 50-ms pulses, 5-second intertrain interval) through a linked pair of custom acetal homopolymer probes (aka TAC-Cells) adhered to the nonglabrous skin of the lower face proximal to the right oral angle to synchronously activate mechanoreceptive afferents in the trigeminal nerve. Blocks of pulse trains were counterbalanced among participants and delivered at two rates, 2 and 4Hz.TAC-Cell stimulation of the lower face consistently evoked a series of cSEPs at P7, N20, P28, N38, P75, N85, and P115. The spatial organization and adaptation of the evoked cSEP was dependent on stimulus pulse index (1–6 within the pulse train, p=.012), frequency of stimulus presentation (2 vs 4Hz, p<.001), component (P7-P115, p<.001), and recording montage (channels 1–4, p<.001). Early component latencies (P7-N20) were highly stable in polarity (sign) and latency, and consistent with putative far-field generators (e.g., trigeminal brainstem, ventroposteromedial thalamus).

Evaluation of CO2-philicity of poly(vinyl acetate) and poly(vinyl acetate-alt-maleate) copolymers through molecular modeling and dissolution behavior measurement.

Multiscale molecular modeling and dissolution behavior measurement were both used to evaluate the factors conclusive on the CO2-philicity of poly(vinyl acetate) (PVAc) homopolymer and poly(vinyl acetate-alt-maleate) copolymers. The ab initio calculated interaction energies of the candidate CO2-philic molecule models with CO2, including vinyl acetate dimer (VAc), dimethyl maleate (DMM), diethyl maleate (DEM), and dibutyl maleate (DBM), showed that VAc was the most CO2-philc segment. However, the cohesive energy density, solubility parameter, Flory-Huggins parameter, and radial distribution functions calculated by using the molecular dynamics simulations for the four polymer and polymer-CO2 systems indicated that poly(VAc-alt-DBM) had the most CO2-philicity. The corresponding polymers were synthesized by using free radical polymerization. The measurement of cloud point pressures of the four polymers in CO2 also demonstrated that poly(VAc-alt-DBM) had the most CO2-philicity. Although copolymerization of maleate, such as DEM or DBM, with PVAc reduced the polymer-CO2 interactions, the weakened polymer-polymer interaction increased the CO2-philicity of the copolymers. The polymer-polymer interaction had a significant influence on the CO2-philicity of the polymer. Reduction of the polymer-polymer interaction might be a promising strategy to prepare the high CO2-philic polymers on the premise that the strong polymer-CO2 interaction could be maintained.

Development of elastic and plastic properties of polyoxymethylene during bending fatigue

ABSTRACTThe development of the plastic and viscoelastic properties and the corresponding failure limits of the acetal homopolymer polyoxymethylene were studied in unidirectional cyclic fatigue. Samples with molecular weights (MWs) ranging from 90 to 142 kg/kmol were tested in displacement‐controlled conditions, resulting in maximum stress amplitudes between 30 and 59 MPa and strain amplitudes between 35.8 and 92.6 με. The zero‐hour material properties and the cycle‐dependent property development were predominantly dictated by deformations in the crystalline regions and showed a negligible dependence on MW. However, the final failure limits were found to be primarily dependent on the length of the amorphous tie chains that connect the crystallites. As such, fatigue life analysis showed a strong dependence on MW. Results are interpreted in light of the primary mechanical failure mechanisms and the corresponding molecular deformations. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40762.

Starve fed emulsion copolymerization of vinyl acetate and 1‐hexene at ambient pressure

A novel emulsion copolymer of vinyl acetate (VAc) and 1‐hexene was synthesized at ambient pressure. The feeding technique, initiation system and reaction time of the copolymerization were optimized based on molecular characteristics such as the weight contribution of 1‐hexene in the copolymer chains and glass transition temperature (Tg) as well as on bulk properties like minimum film‐formation temperature (MFFT) and solid content. According to nuclear magnetic resonance spectroscopy and differential scanning calorimetry results, the combination of starve feeding and redox initiation, within a reaction time of 4 h, effectively led to the copolymerization at ambient pressure between highly reactive polar VAc monomers and non‐polar 1‐hexene monomers of low reactivity. The copolymer showed a lower Tg and MFFT, and a reasonable solid content compared to the poly(vinyl acetate) (PVAc) homopolymer. The consumption rate, hydrolysis of acetate groups and chain transfer reactions during the polymerization were followed using infrared spectroscopy. Based on the results, the undesirable reactions between the VAc blocks were hindered by the neighbouring 1‐hexene molecules. Tensile testing revealed an improvement in the toughness and elongation at break of VAc–1‐hexene films compared to PVAc films. © 2014 Society of Chemical Industry

Phase modulation and morphological evolution associated with surface-bound particle ablation

Surface modification of fused silica windows caused by the ablation of surface-bound microparticles under short pulse laser irradiation is investigated and related to beam propagation effects. Particle material dispersal and subsequent surface pitting after multiple pulses of 351 nm, ∼9 J/cm2 laser light were found to depend strongly on material type and particle size. Surface pitting was most significant for opaque materials (aluminum, steel, acetal homopolymer), yielding pits as deep as 600 nm for ∼30 μm diameter particles. Transparent particles (PET polymer, glass) tended to disperse material more widely and caused less pitting (∼100 nm) than the opaque materials. Paraxial light propagation analysis showed that phase objects created by ablated opaque materials resulted in higher peak intensification (∼3x) than those created by transparent materials (∼1.5x). The fragmentation of ablated material is discussed in terms of brittle or ductile failure at high strain rates, indicating reasonable agreement between experiment and theory. An approximation for the laser-induced plasma pressure and size of the dispersal pattern is derived, indicating an inverse correlation with material density.

Rechargeable antimicrobial coatings for poly(lactic acid) nonwoven fabrics

A novel heterocyclic N-halamine acetate homopolymer was synthesized and characterized by ATR-IR, NMR and MALDI-TOF spectroscopy and TGA and DSC analysis. The homopolymer was coated onto poly(lactic acid) (PLA) meltblown nonwoven fabric, and the surfaces were rendered biocidal upon exposure to dilute sodium hypochlorite solution. The coatings were quite stable versus UVA and florescent light exposure. Moreover, they exhibited long-term shelf-life stability, and they were rechargeable when oxidative chlorine on the surfaces was partially exhausted after three months storage. It was found that the chlorinated fabrics exhibited effective antimicrobial activity with about six logs inactivation of Staphylococcus aureus and Escherichia coli O157:H7 within 30 min of contact time. The coated PLA possesses potential for use in antimicrobial food packaging, filters, and hygiene products.

Photochemical degradation study of polyvinyl acetate paints used in artworks by Py–GC/MS

Photochemical degradation of commercial polyvinyl acetate (PVAc) homopolymer and PVAc paints mixed with burnt umber, cobalt blue, cadmium red dark, nickel azo yellow and titanium white commonly used for artworks were studied by pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) and Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). Py–GC/MS with single-shot technique was used for the characterization of the thermal degradation of PVAc at different temperatures, while the double-shot technique of Py–GC/MS was used to reveal the differences in the specimens before and after UV ageing, including the changes of detectable amounts of deacetylation product – acetic acid and plasticizers such as diethyl phthalate (DEP). Furthermore, the relative concentration of the pyrolysis products of the paint samples could be measured and compared in the second step of the double-shot Py–GC/MS, which are highly dependent on the presence of pigments and the ageing status of PVAc paints.

Tribological effects of polymer surface modification through plastic deformation

The efficacy of using polymers in cylindrical applications depends closely on its surface friction and wear characteristics. In this regard, a surface modification technique through plastic deformation has been implemented. Roller burnishing is commonly used to improve the surface quality of non-ferrous surfaces, but no work showed concern about roller burnishing as a polymer surface treatment process. The objective of the present work is to investigate the influence of burnishing force and burnishing speed on the friction and wear performance of acetal homopolymer and polyurethane under dry and lubricated sliding conditions. The results reveal that the coefficient of friction and wear rate decreased to a minimum value and then increased as higher burnishing force and speed were applied. It was shown that roller burnishing had favourable prospective to be utilized as a valuable polymer surface treatment technique.

Combined XPS and contact angle studies of ethylene vinyl acetate and polyvinyl acetate blends

In this study, we prepared thin films by blending ethylene vinyl acetate copolymers (EVA) containing 12–33 (wt.%) vinyl acetate (VA) with polyvinyl acetate (PVAc) and high density polyethylene homopolymers. Large area micropatterns having controlled protrusion sizes were obtained by phase-separation especially for the PVAc/EVA-33 blends using dip coating. These surfaces were characterized by XPS and contact angle measurements. A reasonably linear relation was found between the VA content on the surface (wt.%) obtained from XPS analysis and the VA content in bulk especially for PVAc/EVA-33 blend surfaces. PE segments were more enriched on the surface than that of the bulk for pure EVA copolymer surfaces similar to previous reports and VA enrichment was found on the EVA/HDPE blend surfaces due to high molecular weight of HDPE. Water θ e decreased with the increase in the VA content on the blend surface due to the polarity of VA. A good agreement was obtained between γ s − and atomic oxygen surface concentration with the increase of VA content. The applicability of Cassie–Baxter equation was tested and found that it gave consistent results with the experimental water contact angles for the case where VA content was lower than 55 wt.% in the bulk composition.