Formaldehyde release from a model N-methylol system

A model N-methylol reactant system based on pyrrolidone derivatives has been used to study the chemical factors that control formaldehyde release. Fabric samples of known composition were prepared from chemically pure reactants and formaldehyde release was determined by the AATCC Sealed Jar Test. This work provides support for prior suggestions and a more direct approach for understanding unexpected results from tests on post-and precure fabrics. In addition, new findings demonstrate that the N-methylol reactant, its byproducts, and pure zinc nitrate are capable of reducing the level of formaldehyde release.     

Assessing the fire behavior of woods modified by N-methylol crosslinking,thermal treatment,and acetylation

Wood products are often treated by different techniques to improve their longevity when used as building materials. Most of the time, the goal is to increase their resistance to weathering effects, deformations in material dimensions or biotic decomposition. These wood treatment techniques have a significant impact on pyrolysis and burning behavior. The general effects of three different common wood treatments on flame retardancy were investigated by comparing treated woods with their untreated counterparts and with other kinds of wood. While the acetylation of beech leads to a slightly increased fire hazard, the thermal treatment of wood and crosslinking of cellulose microfibrils dimethyloldihydroxy-ethyleneurea show a limited flame retarding effect. Switching to woods with a higher lignin content, and thus higher char yield, however, results in a more pronounced improvement in flame retardancy performance. This article delivers a comprehensive and balanced assessment of the general impact of different wood modifications on the fire behavior. Further, it is a valuable benchmark for assessing the flame retardancy effect of other wood modifications.     

The adsorption mechanism of poly-methyl methacrylate microparticles onto paper cellulose fiber surfaces without crosslinking agents

In this work, poly- (methyl methacrylate) microparticles were effectively adsorbed onto the paper cellulose fiber surfaces during impregnation without crosslinking agents. The adsorption behavior and mechanism of microparticles onto paper cellulose fibers were further examined by physical and chemical property characterization in combination with adsorption kinetic model. We reported that the kinetic adsorption process included three phases: rapid adsorption, saturated adsorption, and equilibrium adsorption. Intermolecular hydrogen bonds which increased gradually with the increase of the mass concentration of PMMA microparticles occurred between the carboxyl group of PMMA microparticles and the hydroxyl group of paper cellulose fibers. Due to the increase of the interaction, the crystallinity-index of the paper cellulose decreased. Furthermore, the hydrophobic interaction also occurred between PMMA microparticles and the paper fibers, leading to preferential adsorption of the microparticles on the surfaces of the hydrophobic (2 0 0) crystal cellulose.     

Graft copolymerization of vinyl monomers on modified cottons. XVIII. Grafting of methyl methacrylate and acrylonitrile on cotton treated with N-methylol crosslinking agents using tetravalent cerium as initiator

Ce^IV-induced grafting of methyl methacrylate and acrylonitrile on cotton fibers crosslinked with dimethylol ethylene urea, dimethylol dihydroxyethylene urea, and dimethylol carbamate was investigated. The graft yields obtained with crosslinked cotton were signifcantly lower than the untreated cotton, irrespective of the crosslinking agent and the monomer used. However, the extent and rate of grafting depended upon the degree of crosslinking and the nature of monomer. Based on the magnitude of grafting and Ce^IV consumption during grafting and oxidation of the untreated and crosslinked cottons, the different reactions occurring during grafting of vinyl monomers on these modified cottons were elucidated.     

Level fast dyeing of wool with nucleophilic amino-alkyl dyes and crosslinking agents-Part 2: using bifunctional crosslinking agents

Covalently binding dyes through reactions between commercially available bi-functional crosslinking agents, wool and aminoethylaminotriazinyl dyes is discussed. In particular, dye fixation, levelness and fastness properties have been assessed and shown to be very promising. The proposed system offers the dyer the opportunity to achieve covalent bonding of the dye to the fibre in a controlled manner, thus ensuring good levelness.     

Chemical crosslinking of hydroxypropyl cellulose and chitosan blends

Two liquid crystal forming polysaccharides, hydroxypropyl cellulose and chitosan, were blended in aqueous acetic acid solutions and were crosslinked with dialdehydes (glyoxal and glutaraldehyde) as crosslinker and hydrochloric acid as catalyzer. The crosslinkability, morphology, solubility, and tensile properties of the cross linked blend films are determined and the dependence of those properties on the blend composition and on crosslinker species are discussed. The crosslinked blend films cast from the aqueous acetic acid solutions were amorphous. The solubility, Young's modulus, and tensile strength of the crosslinked blend films greatly depended on blend composition; those properties appeared to exhibit a maximum and a minimum around given blend compositions. The solubility for the crosslinked blend film cast from glyoxal system was greater than that from glutaraldehyde one. © 1996 John Wiley & Sons, Inc.     

Chemical modification of cellulose acetate by allylation and crosslinking with siloxane derivatives

A new pathway to cellulose–siloxane hybrid materials was investigated. Allylated cellulose was prepared by chemical modification of cellulose acetate using three different procedures and was crosslinked afterwards by hydrosilylation in the presence of Karstedt's catalyst. Poly[dimethyl(methyl‐H)siloxane] with 25 mol% Si? H side groups and 1,1,3,3‐tetramethyldisiloxane were used as crosslinking agents in different ratios as regards the unsaturated component. The occurrence of the reaction was verified using Fourier transform infrared spectrometry following the reduction until disappearance of bands corresponding to Si? H and C?C bonds with the formation of new Si? C bonds that led to the crosslinking of the cellulose derivative. The reaction products were processed as films that were insoluble in common solvents. Surface (static contact angle, water vapour sorption capacity and swelling in various solvents), mechanical and thermal properties of the networks processed as films were investigated and the results were correlated with the reactant ratios. The crosslinking density was determined based on differential scanning calorimetry data. Copyright © 2012 Society of Chemical Industry     

Kinetic data for the crosslinking reaction of polycarboxylic acids with cellulose

Kinetic data (rate constant, Arrhenius activation energy, frequency factor) of the esterification of polycarboxylic acids (butane-1, 2, 3, 4-tetracarboxylic acid, citric acid and pyromellitic acid) have been determined by means of isocratic HPLC measuring the portion of polycarboxylic acid that does not react with cellulosic material. The order of activation energy is as follows: citric acid > butane-1, 2, 3, 4-tetracarboxylic acid > pyromellitic acid.     

Polymeric multifunctional carboxylic acids as crosslinking agents for cotton cellulose: Poly(itaconic acid) and in situ polymerization of itaconic acid

Multifunctional carboxylic acids have been used as nonformaldehyde durable press finishing agents for cotton. In previous research we found that maleic acid (MA) and itaconic acid (IA) polymerize in situ on cotton fabric at elevated temperatures when both potassium persulfate (K₂S₂O₈) and sodium hypophosphite (NaH₂PO₂) are present, thus imparting wrinkle resistance to the treated cotton fabric. We also found that MA and IA polymerize in aqueous solutions in the presence of K₂S₂O₈ and NaH₂PO₂. In this research, we compared the effectiveness of poly(itaconic acid) (PIA) applied to cotton fabric as a polymer and IA applied as a monomer and allowed to polymerize in situ for crosslinking cotton cellulose. We found that IA is more effective in esterifying cotton cellulose and imparting a high level of wrinkle resistance to the fabric as it polymerizes in situ than PIA applied as a polymer. We also found that tensile strength loss of the cotton fabric crosslinked by IA polymerizing in situ as a function of fabric wrinkle recovery angle is practically the same as that crosslinked by PIA applied as a polymer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 319–326, 2001     

Robust hydrogel of regenerated cellulose by chemical crosslinking coupled with polyacrylamide network

Regenerated cellulose/polyacrylamide (RC/PAAm) double network (DN) hydrogels are composed of cellulose crosslinked by epichlorohydrin (ECH) and chemical-crosslinked PAAm. The prepared RC/PAAm DN hydrogels present enhanced strength, good shape recovery property, excellent energy dissipation properties, decreased equilibrium water content, and low equilibrium swelling ratio (SR). The compressive strength and modulus of RC/PAAm hydrogel are about 4.3 and 11.5 times compared to that of RC hydrogel, respectively. Intriguingly, the chemical crosslinking between ECH and cellulose chains could increase the distance between cellulose chains. Consequently, the increasing molar ratio of ECH to glucose leads to larger SRs and decreased mechanical strength of the hydrogels. Additionally, higher PAAm contents lead to more densely crosslinked networks, and thus decreasing the SRs and improving the mechanical strength of the hydrogels. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47811.     

Pluronics as crosslinking agents for collagen: novel amphiphilic hydrogels

A series of Pluronic samples (L61, L121, F68, F108) were investigated as collagen crosslinking agents to determine their ability to improve the Young's modulus of a collagen hydrogel, while simultaneously serving as surfactants for single‐walled carbon nanotubes (SWNTs). The crosslinked collagen matrices were prepared by blending type I bovine collagen with either Pluronics or SWNTs dispersed in an aqueous Pluronic solution and crosslinked utilizing carbodiimide chemistry. The resulting material was a crosslinked collagen hydrogel with sufficient mechanical strength to be manipulated and transferred without damaging the matrix. Differential scanning calorimetry confirmed a change in the denaturation temperature for hydrogels prepared using Pluronic or Pluronic/SWNT solutions. Water uptake analysis confirmed the crosslinked matrices to be hydrogels. These collagen hydrogels produced with Pluronics as the crosslinking agents exhibited a Young's modulus 3 to 9 times greater than collagen hydrogels produced in the absence of any crosslinking agent, regardless of polymer molecular weight. However, non‐covalent incorporation of SWNTs was not found to affect the Young's modulus of the resulting collagen hydrogels at the incorporation levels achieved with the Pluronics surfactants. Copyright © 2010 Society of Chemical Industry     

Pore and crosslinking structures of cotton cellulose crosslinked with DMDHEU‐maleic acid

Two dicarboxylic acids (maleic acid and tartaric acid) were used in conjunction with DMDHEU as the crosslinking agents to treat cotton fabric samples. The treated fabrics then were dyed with direct red 81. The results show that the values of the dye absorption, equilibrium absorption, rate constants, and the pore index of structural diffusion resistance constant for the various crosslinking agents are ranked as DMDHEU‐tartaric acid > DMDHEU‐maleic acid > DMDHEU alone at the same dyeing temperature. The activation energies for the three crosslinked fabrics are in the rank of DMDHEU > DMDHEU‐maleic acid > DMDHEU‐tartaric acid. The CL length values for the various crosslinking agent systems are in the series of DMDHEU‐tartaric acid > DMDHEU‐maleic acid > DMDHEU alone for a given number of CL/AGU. The values of the pore index of structural diffusion resistance constant and dyeing rate constant are increased with the increase of CL length. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 143–148, 2005     

Graft copolymerization of acrylic acid onto cellulose: Effects of pretreatments and crosslinking agent

The graft copolymerization of acrylic acid (AA) and 2‐acrylamido 2‐methylpropane sulfonic acid (AASO₃H) onto cellulose, in the presence or absence of crosslinking agent N,N′‐methylene bisacrylamide (NMBA), by using different concentrations of ceric ammonium nitrate (CAN) initiator in aqueous nitric acid solution at either 5 or 30°C was investigated. To investigate the effect of pretreatment of cellulose on the copolymerization, before some grafting reactions cellulose was pretreated with either 2 or 20 wt % NaOH solutions or heated in distilled water/aqueous nitric acid (2.5 × 10^?3 M) at 55°C. To determine how the excess of initiator affects the grafting and homopolymerization, separate reactions were carried out by removing the excess of ceric ions by filtration of the mixture of initiator solution and cellulose before the monomer addition. Extraction‐purified products were characterized by grafting percentage and equilibrium swelling capacity. Pretreatment of cellulose with NaOH solutions decreased the grafting percentage of copolymers. In the case of AA–AASO₃H mixtures, nonpretreated cellulose gave a higher grafting percentage than NaOH‐pretreated cellulose. Filtration also lowered the grafting of AA on the cellulose in the cases of pretreatment with either water or nitric acid. Copolymers with the highest grafting percentage (64.8%) and equilibrium swelling value (105 g H₂O/g copolymer) were obtained in grafting reactions carried out in the presence of NMBA at 5°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2267–2272, 2001     

Reversible crosslinking in cellulose. IV. Reactions of tosylcellulose with potassium thiolacetate

Reactions of tosylated cotton with potassium thiolacetate followed by alkaline hydrolysis yielded products containing both mercaptan and disulfide. The proportion of disulfide in the products depended much on the solvent used for the thiolacetylation. Reactions of tosylcellulose with thiolacetate in various solvents were investigated by polarographic and infrared analyses. Part of the acetylthio groups produced in acetone or in dimethylformamide was found to undergo rearrangement to form mercaptocellulose acetate. On the other hand, acetylthio groups formed in methanol were found to undergo complete methanolysis to form mercaptocellulose, and most of the mercapto groups thus produced were oxidized before hydrolysis treatment to yield the corresponding disulfide. This could account for the high disulfide proportion in the sample obtained through the reaction of tosylcellulose in methanol. Reaction of tosylcellulose with sodium thiosulfate yielded cellulose disulfide without mercaptan formation.     

Photoinitiated crosslinking of hydroxypropyl cellulose in the isotropic and liquid crystal states

The influence of temperature, concentration, and shear rate on the formation of liquid crystal solutions of hydroxypropyl cellulose (HPC) in DMAc and the preservation of the structure by photoinitiated crosslinking were investigated. The rate of changes in the relaxation pattern for the characteristic band texture of HPC liquid crystals after cessation of shear is inversely proportional to the extent of the crosslinking. This shows that the liquid crystalline structure is preserved upon crosslinking. The molecular orientation of the crosslinked films as a function of mesophase organization and concentration during crosslinking was studied.     

Preparation of biodegradable crosslinking agents and application in PVP hydrogel

Firstly, biodegradable crosslinking agents (BCA) were synthesized by ring‐opening polymerization reaction of lactide, four kinds of which with different molecular weights were got by means of changing the ratio of DL ‐lactide(LA) and glycerol(GL). Then a series of poly(N‐vinyl pyrrolidone) (PVP) hydrogels were prepared successfully by radical polymerization of BCA and N‐vinyl pyrrolidone(NVP). Both the ratio of NVP/BCA and the molecular weight of BCA were used to control the performance of PVP hydrogels, which were measured in terms of the ratio of swelling, contact angle, mechanical properties, and biodegradability in vitro. This study showed that increasing both the ratio of NVP/BCA and the molecular weight of BCA resulted in a low crosslinking density of the hydrogels. The crosslinking density played an important role in determining the properties of biodegradable PVP hydrogels. Both the ratio of NVP/BCA and the molecular weight of BCA contributed to high ratio of swelling. A smaller amount of crosslinking agent caused a lower contact angle, while the molecular weight of BCA had little effect on it. In terms of mechanics of hydrogels on both dry and wet conditions, tensile modulus decreased along with decreasing BCA, while the extension at break increased at the beginning and decreased at the end. In the end, measured by mass loss, biodegradability in vitro of hydrogels had two stages: an initial stage with approximately constant loss of mass (stage 1) followed by a stage with rapid mass loss (stage 2). Both increased content and molecular weight of BCA improved the degradation rate of the hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1515–1521, 2006     

Mechanical and drug release properties of alginate beads reinforced with cellulose

The limited efficacy of alginate as a drug carrier is thought to be due to its poor mechanical stability and durability. In the present study, cellulose/alginate (C/Alg) beads were successfully fabricated by droplet extrusion/precipitation method for drug release of metformin hydrochloride (MH). To evaluate the effects of three different cellulose fibers, including cotton linter (CL), microcrystalline cellulose (MCC), and microfibrillated cellulose (MFC) on the stability and drug release property, the structure and properties of composite beads were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and also mechanical properties, thermogravimetric analysis (TGA), swelling and in vitro drug release properties were assessed. The results indicated that the incorporation of cellulose enhances the mechanical properties and thermal stability of alginate matrix. The peak force values of the alginate beads increased from 4.07 ± 1.64 kg to 11.87 ± 2.61 kg with adding 30 wt % MFC. Cellulose with micro‐ and nanostructures improved the encapsulation efficiency and inhibited the rapid release of alginate in simulated intestinal fluid. It was suggested that cellulose could be an effective modifier to adjust the swelling property, mechanical property, and drug release behavior of alginate beads. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44495.     

Desulfurization performance of polydimethylsiloxane membranes by pervaporation: Effect of crosslinking agents

Polydimethylsiloxane (PDMS), as one of the typical membrane, has been widely applied in gasoline desulfurization via pervaporation. In this work, the PDMS/PVDF composite membranes were prepared by curing PDMS with three different crosslinking agents. They were 3‐Aminopropyltrimethoxylsilane (APTMS), 3‐Glycidyloxypropyltrimethoxylsilane (GPTMS), and 3‐Mercaptopropyltrimethoxylsilane (MPTMS), respectively. These PDMS/PVDF composite membranes were characterized by Fourier transform infrared (FT‐IR), X‐ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and then evaluated by static tensile test, swelling degree test and surface detach experiment. The results showed that A‐PDMS membrane had highest crosslinking density, best anti‐swelling ability and excellent combination between the separation layer and support layer. Moreover, the effect of operation temperature and the feed sulfur content on separation performance were investigated systematically. Experimental results indicated that PDMS membrane crosslinked with APTMS presented the highest enrichment factor with 3.46°C at 45°C, and PDMS membrane crosslinked with MPTMS presented the highest permeation flux with 21.19 kg/(m²·h) at 45°C. Finally, long‐term stability test showed that these PDMS membranes all have desirable stability. POLYM. ENG. SCI., 57:1127–1135, 2017. © 2017 Society of Plastics Engineers     

Some mechanical properties of an epoxy resin system cured with multiple crosslinking agents

Arbitrary cure times and glass transition temperatures are reported for an epoxy resin cocrosslinked by various weight fractions of hexamethylenediamine (HMDA) and m-phenylenediamine (m-PLDA). The glass transition temperatures of the epoxy resin systems studied yielded an excellent fit to an empirical equation developed by Dyvik for copolymers. The cure time parameters were found to be a linear function of the weight fractions of each crosslinking agent present. The mechanical properties of the epoxy resins were measured by an in situ dynamic modulus technique which employed the use of a resin-coated metallic substrate.