Preparation, Air Filtration Performance of a Fluorinated Polyimide/Polyacrylonitrile Nanofibrous Membrane by Electrospinning.

This paper reports the successful fabrication of a new nanofibrous membrane, F-PI/PAN, through electrospinning of polyacrylonitrile (PAN) and fluorinated polyimide (F-PI). The nanofibrous membrane exhibits comprehensive properties for high-temperature filtration and robust PM2.5 (particulate matter with an aerodynamic equivalent diameter of 2.5 microns or less) removal. The introduction of F enhances the hydrophobicity of the PI. The relationship between the hydrophobic performance and the filtration performance of particles is investigated. The chemical group of the composite membrane was demonstrated using FITR, while the surface morphology was investigated using field emission scanning electron microscopy. The TGA results indicated good thermal stability at 300 °C. Various ratios of F-PI membranes were prepared to characterize the change in properties, with the optimal mass ratio of F-PI being 20 wt%. As the proportion of F-PI increases, its mechanical and filtration efficiency properties and hydrophobicity become stronger. The contact angle reaches its maximum of 128 ± 5.2° when PAN:F-PI = 6:4. Meanwhile, when PAN:F-PI = 8:2, the filtration efficiency reaches 99.4 ± 0.3%, and the elongation at break can reach 76%. The fracture strength can also reach 7.1 MPa, 1.63 times that of the pure PAN membrane.

Preparation and Mechanism of Bio-Based Sodium Alginate Fibers with Flame Retardant and Antibacterial Properties.

Flame retardant and antibacterial sodium alginate (SA) fiber were fabricated using the bio-based flame retardant of phytic acid and DL-arginine successively, and then the morphological structures, combustion behavior, thermal stability, and mechanical as well as antibacterial properties of SA fiber were investigated carefully. It is found that when the additional amount of PADL (reaction products of phytic acid and DL-arginine) in SA composite fiber is 20 wt%, its limiting oxygen index (LOI) is 40.0 ± 0.3%, and UL-94 is V-0 grade. The combustion behavior of composite fiber shows that PADL can effectively reduce combustion heat and promote carbon formation. Its peak of HRR (pkHRR) is 5.9% of pure SA fiber, and the residual carbon increases from 23.0 ± 0.1% to 44.2 ± 0.2%. At the same time, the density of the residual carbon increases gradually. PADL can promote SA to form expanded carbon with increasing density, and isolate the heat and volatilization of combustible gases. The guanidine group of DL-arginine can interact with the cell membrane to kill bacteria, and the antibacterial property of SA composite fiber is increased by 30%. This study provides a very ecological, safe, environmentally friendly and simple method to prepare flame retardant and antibacterial SA composite fiber with bio-based materials.

Preparation, filtration, and photocatalytic properties of PAN@g-C3N4 fibrous membranes by electrospinning.

Particulate matter and formaldehyde (HCHO) in closed indoor environments are seriously harmful to human health; hence, techniques for the improvement of air quality have attracted significant attention. PAN@g-C3N4 fibrous membranes with high efficiency, low resistance, and photocatalytic activity were prepared by electrospinning with polyacrylonitrile (PAN) and graphite carbon nitride (g-C3N4), followed by the high-temperature polycondensation of melamine. The addition of g-C3N4 to the nanofibrous membrane effectively improved the filtration efficiency of PM2.5. When the amount of added g-C3N4 was 3 wt%, the filtration efficiency of PM2.5 was 99.76 ± 0.3%, the filtration efficiency was stable for 24 hours at a continuous high concentration, and the filtration cycle stability was good. As a photocatalytic material, g-C3N4 causes the photocatalytic degradation of HCHO, and thus, significantly improves the filtration efficiency of the nanofibrous membrane to HCHO. When the amount of added g-C3N4 was 3 wt%, the filtration efficiency of the nanofibrous membrane to HCHO reached 78.0 ± 1.8%. The mechanism of catalytic degradation showed that the PAN fibres first adsorbed and intercepted the HCHO molecules. Under simulated sunlight irradiation, the photogenerated holes generated by the g-C3N4 nanosheets in the fibres oxidised and decomposed the adsorbed HCHO molecules. This study has broad application potential for high-efficiency filters to improve indoor air quality.

Organic Aluminum Hypophosphite/Graphitic Carbon Nitride Hybrids as Halogen-Free Flame Retardants for Polyamide 6.

The novel organic aluminum hypophosphite (ALCPA) and its hybrid (CNALCPA) with graphitic carbon nitride (g-C3N4) were successfully synthesized and applied as halogen-free flame retardants in polyamide 6 (PA6). Their structures, morphology, thermal stability, and fire properties were characterized. Results showed that both ALCPA and CNALCPA had good flame retardancy. PA6/CNALCPA composites achieved a high limited-oxygen-index (LOI) value of 38.3% and a V-0 rating for UL94 at 20 wt % loading, while PA6/ALCPA composites could reach a V-1 rating for UL94. The flame-retardant mechanism was also studied. On the one hand, the incorporation of g-C3N4 produced more gas-phase products, which indicated a gas-phase mechanism. On the other hand, g-C3N4 could catalyze the thermal degradation of ALCPA and PA6 to form a compact char layer that was evidence for a solid-phase mechanism. The tensile test of the PA6 composites also displayed good mechanical properties.

Modification of Poly(Ethylene 2,5-Furandicarboxylate) with Poly(Ethylene glycol) for Biodegradable Copolyesters with Good Mechanical Properties and Spinnability.

Using 2,5-furandicarboxylic acid, ethylene glycol, and poly(ethylene glycol) as raw materials and ethylene glycol antimony as a catalyst, poly(ethylene furandicarboxylate) (PEF) and polyethylene glycol (PEG) copolymers (PEGFs) were synthesized by transesterification by changing the molecular weight of PEG (from 600 to 10,000 g/mol) and the PEG content (from 10 to 60 wt %). The thermal, hydrophilic, degradation, and spinnility characteristics of these copolymers were then investigated. Thermogravimetric analysis shows that PEGF is thermally stable at 62 °C, much lower than the temperature for PEF. The intrinsic viscosity of the obtained copolyester was between 0.67 and 0.99 dL/g, which is higher than the viscosity value of PEF. The contact angle experiment shows that the hydrophilicity of PEGFs is improved (the surface contact angle is reduced from 91.9 to 63.3°), which gives PEGFs a certain degradability, and the maximum mass loss can reach approximately 15%. Melt spinning experiments show that the PEGF polymer has poor spinnability, but the mechanical properties of the polymer monofilament are better.

Pickering emulsion process assisted construction of regenerated chitin reinforced poly (lactic acid) blends.

Regenerated chitin (RCh)/poly (lactic acid) (PLA) blends with enhanced properties were successfully prepared via the Pickering emulsion approach. An oil-in-water Pickering emulsion of PLA/dichloromethane (DCM) stabilized with RCh via an ultrasonic homogenizer was formed. A uniformly dispersed blends were obtained upon slow volatilization of DCM. The effects of RCh on physical/morphological, thermal, mechanical and rheology properties of the blends were studied. The introduction of RCh in PLA improved its crystallinity from 23.4% to over 38.0%. The blends displayed an improvement in storage modulus of 393% at 70 °C for 2 wt%RCh as compared with neat PLA. The RCh/PLA blends showed an enhancement in both tensile strength and elongation at break of 18% and 31% respectively at the loading of 1.5 wt%-RCh. Moreover, the complex viscosity of the blends was increased compared to neat PLA, and all the blends exhibited shear-thinning behaviour without any plateau region at low angular frequencies (ω < 10 rad/s). These results suggest that the low weight content RCh introduced to PLA matrix via this facile Pickering emulsion approach not only promotes nucleation in RCh/PLA blends but also acts as a promising reinforcing agent for PLA.

A Novel Synthetic Strategy for Preparing Polyamide 6 (PA6)-Based Polymer with Transesterification.

In the polymerization of caprolactam, the stoichiometry of carboxyl groups and amine groups in the process of melt polycondensation needs to be balanced, which greatly limits the copolymerization modification of polyamide 6. In this paper, by combining the characteristics of the polyester polymerization process, a simple and flexible synthetic route is proposed. A polyamide 6-based polymer can be prepared by combining caprolactam hydrolysis polymerization with transesterification. First, a carboxyl-terminated polyamide 6-based prepolymer is obtained by a caprolactam hydrolysis polymerization process using a dibasic acid as a blocking agent. Subsequently, ethylene glycol is added for esterification to form a glycol-terminated polyamide 6-based prepolymer. Finally, a transesterification reaction is carried out to prepare a polyamide 6-based polymer. In this paper, a series of polyamide 6-based polymers with different molecular weight blocks were prepared by adjusting the amount and type of dibasic acid added, and the effects of different control methods on the structural properties of the final product are analyzed. The results showed that compared with the traditional polymerization method of polyamide 6, the novel synthetic strategy developed in this paper can flexibly design prepolymers with different molecular weights and end groups to meet different application requirements. In addition, the polyamide 6-based polymer maintains excellent mechanical and hygroscopic properties. Furthermore, the molecular weight increase in the polyamide 6 polymer is no longer dependent on the metering balance of the end groups, providing a new synthetic route for the copolymerization of polyamide 6 copolymer.

Effects of total solids content on performance of sludge mesophilic anaerobic digestion and dewaterability of digested sludge.

The role of total solids (TS) content on sludge mesophilic anaerobic digestion (AD) was investigated in batch reactors. A range of TS below 10% was evaluated with two replicates. The volumetric biogas production rate (VBPR) increased with increasing initial TS. On day 5, VBPR increased from 133.2±11.2mLL-1d-1 at TS 2% to 1111.7±58.1mLL-1d-1 at TS 10%. The ultimate biogas yield (P) firstly increased and then decreased with the increasing TS. The greatest P was 246.8mLg-1-VSadded at TS 8%. The corresponding free ammonia nitrogen (FAN) and total ammonia nitrogen (TAN) were 84.0±16.1 and 1163.0±108.6mgL-1, respectively. Normalized capillary suction time (NCST) and solid content of thickened sludge obtained by centrifuging sludge increased with increasing TS. On day 49, NCST were 1.2±0.2 (TS=2%) and 13.2±1.1 (TS=10%)sg-1-TS. Meanwhile, solid content of thickened sludge was 7.5±0.5 (TS=2%) and 15.4±0.0% (TS=10%). In summary, high VBPR and dewatering effects were obtained after TS content optimization.

Cellulose synthesized by Acetobacter xylinum in the presence of multi-walled carbon nanotubes.

The structure of bacterial cellulose is affected by the bacterial strain used, culture media and cultivation conditions. In this study, acid-treated multi-walled carbon nanotubes (MWNTs) were added into a static culture medium and their effect on bacterial cellulose structure was studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), CP/MAS (13)C NMR and X-ray diffractometry. The bacterial cellulose ribbons and the MWNTs interwound and formed a three-dimensional network architecture. Band-like assemblies with sharp bends and rigidity were also produced in the presence of MWNTs. The intermolecular hydrogen bonds in bacterial cellulose produced in the presence of MWNTs were weakened. The crystal structure, cellulose I(alpha) content, crystallinity index (CrI) and crystallite size all changed. The results may suggest that the acid-treated MWNTs containing hydroxyl groups interact with the sub-elementary bacterial cellulose fibrils, subsequently interfering with the aggregation and crystallization.