Preparation of highly water-resistant wood adhesives using ECH as a crosslinking agent

In this study, kraft lignin and epichlorohydrin (ECH) were used to prepare no-formaldehyde wood adhesives. The lignin was first treated by ball milling, then reacted with glyoxal to produce glyoxalated lignin under alkaline conditions, and then blended with ECH to prepare lignin-based formaldehyde-free adhesive. The influence of the content of ECH on the physicochemical properties of the adhesives was explored, and the possible synthesis mechanism of the ECH-modified glyoxalated lignin adhesives (glyoxalated kraft lignin-epoxy [GKLE]) was investigated. The results show that ECH was beneficial to improving the plywood shear strength and water resistance; the plywood prepared with GKLE-50 adhesive displays comparable water resistance as phenol–formaldehyde resins and its wet shear strength (type I) was 1.05 MPa, exceeding the Chinese National Standards GB/T 9846-2015. Scanning electron microscopy analysis showed that the increase of ECH content promoted the adhesive to penetrate the wood to form glue nails, improving the wet shear strength of the plywood. Chemical analysis indicated that glyoxalation was used to introduce hydroxyethyl groups into the ortho positions of the aromatic rings of lignin, and then the ring-opening reaction between glyoxalated lignin and ECH occurred forming ether bonds. Overall, lignin has displayed great potential in replacing formaldehyde-based adhesives for industrial applications.

Fused deposition modeling of polypropylene-aluminium silicate dihydrate microcomposites

Polypropylene (PP) undergoes fast crystallization and resulting in rigorous shrinkage when it is subjected to high temperature likewise of the fused deposition modeling (FDM) process. This research study focuses on the investigation of the processing parameters and factors that decrease the warpage of PP during the FDM process. Aluminium silicate dihydrate (K) microparticles of different ratios were melt blended with PP by a twin-screw extruder, and filaments of about 1.7 mm diameter were extruded in a single screw extruder. Then, the extruded filaments were used to fabricate the dumbbells structure through the FDM process. The effects of optimizing the fused deposition temperature, coating the chamber with thick papers/fabrics, and coating a printer bed with PP material were also investigated in this study. Scanning and transmission electron microscopy, differential scanning calorimetry, melt flow, and mechanical properties testing instruments are used to analyze the microparticles dispersion, crystallization, flow, and mechanical properties of resulting samples. Uniformly dispersed filler and increased printing chamber temperature result in an increase of crystallization temperature and improve the dimensional accuracy of fused deposited specimens. The fused deposited PP-K10 wt% composite showed an improvement of up to 32% in tensile modulus compared to the neat PP.

State of the art of geopolymers: A review

Geopolymers emerge as an ecological alternative for construction materials. These consist of a mixture of aluminosilicate sources and an alkaline solution that dissolves the silicon and aluminum monomers that come from the source to generate a gel called N–A–S–H that will control the main properties of the geopolymer. The geopolymer stands out for having good resistance to compression, as well as good resistance to high temperatures and corrosive environments. They have great potential as a replacement for classical technologies such as concrete, however, require further applied research to determine their feasibility on an industrial scale.

The use of chitosan as a skin-regeneration agent in burns injuries: A review

Chitosan is an amino-polysaccharide, traditionally obtained by the partial deacetylation of chitin from exoskeletons of crustaceans. Properties such as biocompatibility, hemostasis, and the ability to absorb physiological fluids are attributed to this biopolymer. Chitosan’s biological properties are regulated by its origin, polymerization degree, and molecular weight. In addition, it possesses antibacterial and antifungal activities. It also has been used to prepare films, hydrogels, coatings, nanofibers, and absorbent sponges, all utilized for the healing of skin wounds. In in vivo studies with second-degree burns, healing has been achieved in at least 80% of the cases between the ninth and twelfth day of treatment with chitosan coatings. The crucial steps in the treatment of severe burns are the early excision of damaged tissue and adequate coverage to minimize the risk of infection. So far, partial-thickness autografting is considered the gold standard for the treatment of full-thickness burns. However, the limitations of donor sites have led to the development of skin substitutes. Therefore, the need for an appropriate dermal equivalent that functions as a regeneration template for the growth and deposition of new skin tissue has been recognized. This review describes the properties of chitosan that validate its potential in the treatment of skin burns.

Fabrication of PANI-modified PVDF nanofibrous yarn for pH sensor

In recent years, with the rise of an intelligent concept, oral and maxillofacial surgery smart dressing had also attracted the interest of researchers, especially for the pH sensor with flexible medium. In this study, polyvinylidene fluoride (PVDF) nanofibrous yarn was fabricated by a conjugate electrospinning process and modified with in situ polymerization of polyaniline (PANI) forming a PANI/PVDF yarn. By a weaving process, these yarns could be weaved into a fabric. It was found that both the PANI/PVDF yarn and the fabric showed a sensitivity to pH, about −48.53 mV per pH for yarn and −38.4 mVper pH for fabric, respectively, in the pH range of 4.0–8.0. These results indicated that the prepared PANI-modified PVDF yarn and fabric might have a potential application in intelligent oral and maxillofacial surgery dressings for monitoring wound healing.

Development, characterization, and in vitro evaluation of adhesive fibrous mat for mucosal propranolol delivery

This research focuses on the synthesis and adhesive properties of mucoadhesive mats, prepared with poly(vinylic alcohol) as a base polymer for the oromucosal release of propranolol (PRO) by the electrospinning technique. The nanofibers mats were evaluated by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry; in vitro drug entrapment efficiency, degradation time, and adhesion studies were performed. SEM images of the electrospun mats show the correct formation of fibers with a variable diameter and porosity. Thermal studies indicate excellent thermal stability of the scaffolds, The fibrous mats loaded with 10% of the drug exhibit the best thermal stability with decomposition after 450°C. In vitro studies indicate a drug content of 88% loaded in the mats. In the cytotoxicity test, loaded mat presents cell proliferations of 97% and 88% for drug concentrations of 10% an 15%, respectively. To conclude, the formed electrospun adhesive mats exhibited excellent thermal stability, adhesive properties, and drug entrapment efficiency, promising features for a successful drug topical release system on mucosal tissue in the oral cavity.

Fabrication of flexible conductive silk fibroin/polythiophene membrane and its properties

Silk fibroin (SF) film is an insulating material, which can be combined with polythiophene derivatives with electrical conductivity to obtain a flexible conductive material. In this work, poly(3,4-ethylenedioxythiophene) (PEDOT) was used to graft a silk protein film. The hydroxyl radical is formed by activation and oxidation of the silk protein film polymerized with the PEDOT radical formed by oxidation of 3,4-ethylenedioxythiophene to obtain a conductive silk film. The SF/PEDOT film, when tested, showed excellent electrical conductivity with resistance up to 63 Ω·cm−2, good flexibility, mechanical properties, fastness, and biocompatibility.

Effect of polyurethane/polyvinyl alcohol coating on mechanical properties of polyester harness cord

In this article, water-based polyurethane (PU) with different concentrations and partial alcoholysis polyvinyl alcohol (PVA) were used to coat polyester (PET) harness cord in turn. The surface and mechanical properties of harness cord before and after coating were evaluated by performing the tests of dynamic contact angle, morphology observation, bending properties, tensile properties, and wearability. It was found that the surface properties of 1.5% PU-coated harness cord tended to be stable, and the mechanical properties of PU(1.5%)/PVA-coated harness cord were optimal. Compared with PVA-coated harness cord, the wearability of PU(1.5%)/PVA-coated harness cord showed a great increment up to 135.7%. This was because the PU coating effectively improved the interfacial properties between the PVA coating and the hydrophobic PET fibers and enhanced the adhesion of the PVA coating to the PET fibers.

The HDPE composites reinforced with waste hybrid PET/cotton fibers modified with the synthesized modifier

Large amounts of textile waste are generated every year and disposed of through landfill or incineration, leading to numerous environmental and social issues. In this study, waste hybrid polyethylene terephthalate (PET)/cotton fibers were used directly to reinforce high density polyethylene (HDPE) to prepare composites. In order to give full play to the fiber’s reinforcing characteristics, the PET/cotton fibers were further modified with the modifier using a novel synthesized tetraethyl orthosilicate/3-aminopropyl triethoxysilane (KH550)/polyethylene (PE)-g-MAH (MPE) hybrid (TMPE). Fourier transform infrared and scanning electron microscopy (SEM) confirmed that the TMPE was successfully coated on the surface of fibers. Furthermore, compared with the original and the MPE-modified fibers, the thermal stability of TMPE-modified fibers was significantly increased. SEM and mechanical test indicated that the compatibility of the modified fibers with HDPE had been significantly improved, which led to the improvement of mechanical properties. Compared with the original and MPE-modified fibers-reinforced HDPE composites, the bending strength, bending modulus, and impact strength of TMPE-modified fiber-reinforced HDPE composites were improved obviously by 31.7%, 25.7%, and 89.1%, respectively.

Hyper-crosslinked polymers with controlled multiscale porosity for effective removal of benzene from cigarette smoke

A series of hyper-crosslinked polymers (HCPs) with connected hierarchical porous structures were synthesized from phenyl-based precursors of benzene (BEN), benzyl alcohol, aniline, biphenyl, and 1,3,5-triphenylbenzene (TPB) via the knitting method. The porous structures of the HCPs were greatly influenced by substituent groups and BEN ring number in the precursors. HCPs prepared from TPB had the largest surface area and pore volume with multiscale porosity. The porous structure of the HCPs could also be adjusted by the crosslinker amount. Insufficient crosslinking led to incomplete pore architecture, while excessive crosslinking resulted in a considerable decrease in the pore volume. With these HCPs as adsorbents, the BEN yield in the cigarette smoke could be largely reduced due to the connected multiscale porosity and π–π aromatic stacking interaction that facilitated the smoke aerosol passing and the small aromatic molecules absorbing, showing great potential of these HCPs as adsorbents for effective removal of BEN from cigarette smoke.