On the Network Strength of Meta-Aramid Fiber Suspension and Its Relationship to Formation

Because of poor surface hydrophilicity, meta-aramid fibers readily form flocs by intertwining or interlacing, and this severely affects the uniformity of meta-aramid paper. To investigate the flocculation mechanism of meta-aramid fiber suspensions, the critical flocculant concentration, shear, and compressive network strength of meta-aramid fiber suspensions were examined. A hand sheet former was used to study the influence of the yielding properties of suspensions on the uniformity of meta-aramid paper, and the relationship between the formation index and rheological properties was determined. The results showed that the critical gel concentration ranged from 0.37 to 0.68 g/L, which was much lower than that of plant fiber suspensions. In addition, the compressive yield stress ( P y ) and shear yield stress ( τ y ) of the meta-aramid fiber suspensions were found to increase linearly and exponentially, respectively, with an increasing concentration, and the uniformity index of the paper sheets was found to depend on a power of τ y ⋅ P y . This provides an effective method for predicting paper sheet uniformity.

Highly Effective Crosslinker for Redox-Sensitive Gene Carriers

Polyethyleneimine (PEI) has been extensively used as a common gene carrier due to its high gene transfection efficiency. PEI1.8k shows significantly lower cytotoxicity than its high molecular weight counterparts. However, it also has the problem of low gene transfection efficiency. To address the dilemma, a highly effective crosslinker (DTME) was synthesized to react with PEI1.8k to obtain CS-PEI1.8k. The reaction showed several advantages, such as a fast process in room temperature within nine hours with the product which can directly complex with DNA after removing the solvent. The ability of CS-PEI1.8k to agglomerate with DNA was proven by particle size, zeta potential, and gel retardation assays. The cytotoxic in vitro transfection ability and cell internalization capacity of CS-PEI1.8k were tested to verify the transfection capacity of CS-PEI1.8k. Moreover, we also studied the mechanism of the relatively high level of gene transfection by this binary complex compared with PEI25k.

Facile Production of Graphene/Polypropylene Composites with Enhanced Electrical and Thermal Properties through In Situ Artificial Latex Preparation

In order to obtain the unique properties of graphene-based composites, to realize homogeneous dispersion of graphene throughout the polymer matrix remains the key challenge. In this work, edge-oxidized graphene/polypropylene (EOGr/PP) composites with well-dispersed EOGr in PP matrix, synchronously exhibiting high electrical conductivity and thermal property, were simply fabricated for the first time using a novel strategy by in situ artificial PP latex preparation in the presence of EOGr based on solution-emulsification technique. The good dispersion state of EOGr in the PP matrix was demonstrated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A blue shift in Raman G peak of the EOGr nanosheets was observed in the EOGr/PP composites, indicating the strong interactions between the EOGr nanosheets and the PP matrix. The onset crystallization and crystallization peak temperatures increased as the EOGr loading increases due to its good nucleating ability. An improved thermal stability of EOGr/PP composites was observed as evaluated by TGA. The EOGr/PP composites showed an insulator-to-conductor percolation transition in between that of 1 and 2 wt% EOGr content. Such strategy provides a very effective pathway to fabricate high-performance nonpolar polymer/graphene composites with excellent dispersion state of graphene.

Effect of Lanthanum Cerium Cysteine on Cure Characteristics, Mechanical Properties, and Thermooxidative Aging for Natural Rubber

In this work, a novel additive lanthanum cerium cysteine (LC-Cys), with the molecular formula La0.35Ce0.65(Cys)3Cl3·3H2O, was successfully synthesized through complex decomposition reaction of L-Cysteine and chlorinated rare earths. The effects of additive LC-Cys on cure characteristics, mechanical properties, and thermooxidative aging were investigated. LC-Cys as a multifunctional additive was applied to increase the curing rate and reduce the content of zinc oxide in the presence of the sulfur vulcanization system. It was found that the vulcanizates filled with (5ZnO/2LC-Cys) exhibited the highest modulus, which indirectly indicated the high crosslink and stiffness of the vulcanizates. Moreover, the vulcanizates with LC-Cys showed excellent mechanical properties and resistance to thermooxidative aging. Compared to NR composites filled with normal ZnO, LC-Cys even enhanced the mechanical strength and thermooxidative aging properties with 40% lower ZnO addition.

Predicting the Swelling Behavior of Acrylic Superabsorbent Polymers Used in Diapers

Acrylic polymer is a superabsorbent for water and widely used in diapers, in which its swelling behavior can be significantly affected by several factors, i.e., the time, temperature, pH, and salt concentration, and thus the product performance in the applications. In this work, the water absorption behavior of acrylic superabsorbent polymers by each of these individual factors was investigated. The results showed that the water absorbency increases with the pH in the range of 2 to ~7 and decreases when the pH continues to increase. However, it decreases with the increases in NaCl concentration in the solution. Moreover, more water can be absorbed by the acrylic polymers at the higher temperature. Based on a previously developed kinetic swelling model and the information from the above investigations, a semiempirical model for predicting the swelling behavior of superabsorbent polymers (SAPs) under different conditions has been developed. Data showed that the model can predict (with a relative error of <4.5%) the amount of water absorbed by acrylic SAPs under different swelling conditions. The model would be very helpful to the practical application in both product design and its performance evaluation.

Apparent Molecular Weight Distributions for Investigating Aging in Polymer-Modified Bitumen

The oxidative aging of bituminous binders affects the performance and durability of pavements. In the case of polymer-modified binders, aging involves both bitumen and polymers and has a strong impact on the whole architecture of the material. Rheology may help in understanding these structural changes, and interesting information may be obtained by analysing the evolution of apparent molecular weight distributions. This was demonstrated with a bituminous binder modified with a poly(styrene-butadiene) block copolymer and subjected to prolonged artificial aging. Isothermal frequency sweep tests were used to construct master curves of the phase angle and magnitude of the complex modulus. The master curves were then used to calculate relaxation spectra and apparent molecular weight distributions of the binders, as well as simulated temperature sweep tests. A comparison of the behaviour of the base and modified bitumen highlighted the role of the polymer in aging. Polymer degradation significantly damages the elastomeric network, yet the residual polymer chains still interact with the bitumen molecules and reduce their oxidative aging. The apparent molecular weight distributions were deconvoluted to create an aging index specifically developed for polymer-modified bitumen.

Effect of Sepiolite-Loaded Fe2O3 on Flame Retardancy of Waterborne Polyurethane

In this study, a kind of inorganic composite flame retardant (Sep@Fe2O3) was prepared by combining solution deposition and calcination methods using sepiolite microfiber material as carrier. This inorganic compound flame retardant was combined with waterborne polyurethane (WPU) through layer-by-layer method to prepare WPU composites. The SEM and EDS, TEM, and XRD were used to characterize the microscopic morphology and crystal structure of WPU composites. Thermogravimetric analysis tests confirmed the good thermal stability of WPU/Sep@Fe2O3 composites; at the temperature of 600°C, the carbon residual percentage of WPU/Sep, WPU/Fe2O3, and WPU/Sep@Fe2O3 composites is 7.3%, 12.2%, and 13.4%, respectively, higher than that of WPU (1.4%). Vertical combustion tests proved better flame-retardant property of WPU/Sep@Fe2O3 composite-coated cotton than noncoated cotton. The microcalorimeter test proved that the PHRR of WPU/Sep@Fe2O3 composites decreased by 61% compared with that of WPU. In addition, after combining with Sep@Fe2O3, the breaking strength of WPU increased by 35%.

Antialgal Synergistic Polystyrene Blended with Polyethylene Glycol and Silver Sulfadiazine for Healthcare Applications

Polystyrene (PS) was blended with polyethylene glycol (PEG) and silver sulfadiazine (SS) with different weight proportions to form polymeric blends. These synthesized blends were preliminary characterized in terms of functional groups through the FTIR technique. All compositions were subjected to thermogravimetric analysis for studying thermal transition and were founded thermally stable even at 280°C. The zeta potential and average diameter of algal strains of Dictyosphaerium sp. (DHM1), Dictyosphaerium sp. (DHM2), and Pectinodesmus sp. (PHM3) were measured to be -32.7 mV, -33.0 mV, and -25.7 mV and 179.6 nm, 102.6 nm, and 70.4 nm, respectively. Upon incorporation of PEG and SS into PS blends, contact angles were decreased while hydrophilicity and surface energy were increased. However, increase of surface energy did not led to decrease of antialgal activities. This has indicated that biofilm adhesion is not a major antialgal factor in these blended materials. The synergetic effect of PEG and SS in PS blends has exhibited significant antialgal activity via the agar disk diffusion method. The PSPS10 composition with 10 w / w % PEG and 10 w / w % SS has exhibited highest inhibition zones 10.8 mm, 10.8 mm, and 11.3 mm against algal strains DHM1, DHM2, and DHM3, respectively. This thermally stable polystyrene blends with improved antialgal properties have potential for a wide range of applications including marine coatings.

Continuous Differential Microemulsion Polymerization to Prepare Nanosized Polymer Latices in Microreactors

Microreactors are a promising platform for continuous synthesis of polymer latices when combined with emulsion polymerization. However, this application has long been haunted by fouling and clogging problems. In this work, we proposed the strategy of conducting differential microemulsion polymerization in microreactors within a biphasic slug flow and achieved rapid and stable preparation of nanosized PMMA latices (polymeric content as high as 15.7% with average particle size smaller than 20 nm). We started by exploring the temperature thresholds with thermal and redox initiation, the effect of initiator concentration, and the kinetic characteristics of microemulsion polymerization at different temperatures. Then, as for the differential microemulsion polymerization, extensive investigation was made into the effects of the volumetric flow ratio, the prepolymerization time, the initiator concentration, and the solid content of the initial microemulsion. Finally, we compared the differential microemulsion polymerization with the soap-free emulsion polymerization in the slug flow. The striking advantages in the polymerization rate, the average particle diameter, and the size distribution reflected higher density of particle nuclei, larger specific surface area of particles, and the pivotal effect of the persistent particle nucleation in the microemulsion polymerization.

Effects of the Interfacial Bonding Behavior on the Mechanical Properties of E-Glass Fiber/Nanographite Reinforced Hybrid Composites

The nanoparticles are incorporated into the composite to mark their unique properties. This work investigates the hybrid epoxy nanocomposite and the impact of nanographite reinforcement. The composite was prepared by using a mechanical stirring technique. The amount of nanographite was added in different volumes, i.e., 1.0, 1.5, and 2.0 wt.%. Results of mechanical and dynamic loading properties were analyzed in accordance to the quantity of nano-G. The fiber and matrix interfacial bonding enrichments were evident in high-resolution SEM images-tensile fracture surface. Finally, the optimum content of nanoparticle which impacts the sample greatly was found to be 1.5 wt.%.