Interfacial interactions and the polymer/polyurethane bond

Lap shear measurements of adhesion in joints of polymers bonded with polyurethane adhesives varied significantly with time at elevated temperature. The effect has been linked with the ability of polyurethane molecules to restructure in response to the orienting strength of substrate surfaces, as defined by their non-dispersive surface energy component. Acid/base interactions at the polymer/adhesive interface further affect the bond strength, increasing this important property when acid/base pairs are located at the interface, and diminishing the variable when acid/base interactions are absent.     

Effects of Alcell Lignin Methylolation and Lignin Adding Stage on Lignin-Based Phenolic Adhesives

To investigate the effects of lignin methylolation and lignin adding stage on the resulted lignin-based phenolic adhesives, Alcell lignin activated with NaOH (AL) or methylolation (ML) was integrated into the phenolic adhesives system by replacing phenol at various adhesive synthesis stages or directly co-polymerizing with phenolic adhesives. Lignin integration into phenolic adhesives greatly increased the viscosity of the resultant adhesives, regardless of lignin methylolation or adding stage. ML introduction at the second stage of adhesive synthesis led to much bigger viscosity than ML or AL introduction into phenolic adhesives at any other stages. Lignin methylolation and lignin adding stage did not affect the thermal stability of lignin based phenolic adhesives, even though lignin-based adhesives were less thermally stable than NPF. Typical three-stage degradation characteristics were also observed on all the lignin-based phenolic adhesives. Three-ply plywoods can be successfully laminated with lignin based adhesives, and it was interesting that after 3 h of cooking in boiling water, the plywoods specimens bonded with lignin-based phenolic adhesives displayed higher bonding strength than the corresponding dry strength obtained after direct conditioning at 20 °C and 65% RH. Compared with NPF, lignin introduction significantly reduced the bonding strength of lignin based phenolic adhesives when applied for plywood lamination. However, no significant variation of bonding strength was detected among the lignin based phenolic adhesives, regardless of lignin methylolation or adding stages.     

Polyaniline/lignin blends: FTIR, MEV and electrochemical characterization

Blends of polyaniline (emeraldine base) and Eucalyptus grandis kraft lignin were prepared by casting method. The maximum amount of lignin that could be used for blending was 36% (w/w); beyond that, fractile films were produced. The IR spectra of the blends indicated that interactions occurred between polyaniline and lignin. Cyclic voltammetry measurements showed peaks that were readily attributed to the oxidation/reduction of polyaniline and a new oxi-reduction peak due to oxidation/reduction of sites created during interaction of two polymers. Scanning electronic microscopy showed that all blends were homogeneous.     

Influence of molecular weight distribution and long chain branching on the glass transition temperature of polycarbonate

Molecular weight distribution and long chain branching were taken into account for the glass transition temperature (Tg)-molecular weight (M) relationships for bisphenol-A polycarbonate. A new form of the four-variable equation for Tg is proposed for polydisperse branched polymers. The extended equations were compared with the experimental results on Tg and M averages; they were also applied for characterization of branched polymer by the combined GPC/V and DSC methods.     

Effects of SEBS-g-BTAI on the morphology, structure and mechanical properties of PA6/SEBS blends

Styrene-b-(ethylene-co-1-butene)-b-styrene (SEBS) triblock copolymer functionalized with ε-caprolactam blocked allyl (3-isocyanate-4-tolyl) carbamate (SEBS-g-BTAI) was used to toughen polyamide 6 (PA6) via reactive blending. Compared to the PA6/SEBS blends, mechanical properties such as tensile strength, Young’s modulus, especially Izod notched strength of PA6/SEBS-g-BTAI blends were improved distinctly. Both rheological and FTIR results indicated a new copolymer formed by the reaction of end groups of PA6 and isocyanate group regenerated in the backbone of SEBS-g-BTAI. Smaller dispersed particle sizes with narrower distribution were found in PA6/SEBS-g-BTAI blends, via field emitted scanning electron microscopy (FESEM). The core-shell structures with PS core and PEB shell were also observed in the PA6/SEBS-g-BTAI blends via transmission electron microscopy (TEM), which might improve the toughening ability of the rubber particles.     

Studies on thermal characterization of lignin

Thermal properties of control phenol formaldehyde (cpf) adhesive and lignin substituted phenol formaldehyde (lpf) adhesives have been investigated in detail. The effect of varying lignin mass percent of phenol and source of lignin like bagasse, eucalyptus bark, coconut coirpith and coffee bean shell on the thermal stability have been studied using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). 50 mass% of lignin loading in cpf adhesive shows better bond strength, whereas lignin incorporation up to 25 mass% yields a resin of thermal stability comparable to cpf. Loading of lignin in cpf delays the first thermal transition event. The mass loss in this event was found to increase with increasing lignin content. Lignin source has significant effect on the thermal stability of lpf resins. Rate of curing is enhanced by incorporation of lignin into cpf.     

Recent Developments in the Adhesives Field

The applications of adhesives have been greatly extended by the use of synthetic organic high polymers. It is possible nowadays to bond, not only wood, leather, and paper, but also glass, high-strength plastics, and metals with adhesives of this type. They give satisfactory adhesion, flexibility, and mechanical properties even at high temperatures. A particularly important advance was the introduction of chemically or mechanically blocked polymer systems, which can reduce the cost of curing equipment when used as adhesives.     

Mechanical and Morphological Properties of Bio-Phenolic/Epoxy Polymer Blends

Polymer blends is a well-established and suitable method to produced new polymeric materials as compared to synthesis of a new polymer. The combination of two different types of polymers will produce a new and unique material, which has the attribute of both polymers. The aim of this work is to analyze mechanical and morphological properties of bio-phenolic/epoxy polymer blends to find the best formulation for future study. Bio-phenolic/epoxy polymer blends were fabricated using the hand lay-up method at different loading of bio-phenolic (5 wt%, 10 wt%, 15 wt%, 20 wt%, and 25 wt%) in the epoxy matrix whereas neat bio-phenolic and epoxy samples were also fabricated for comparison. Results indicated that mechanical properties were improved for bio-phenolic/epoxy polymer blends compared to neat epoxy and phenolic. In addition, there is no sign of phase separation in polymer blends. The highest tensile, flexural, and impact strength was shown by P-20(biophenolic-20 wt% and Epoxy-80 wt%) whereas P-25 (biophenolic-25 wt% and Epoxy-75 wt%) has the highest tensile and flexural modulus. Based on the finding, it is concluded that P-20 shows better overall mechanical properties among the polymer blends. Based on this finding, the bio-phenolic/epoxy blend with 20 wt% will be used for further study on flax-reinforced bio-phenolic/epoxy polymer blends.     

Mechanism of adhesion of polyurethane/polymethacrylate simultaneous interpenetrating networks adhesives to polymer substrates

Polyether-based polyurethane/poly (methyl methacrylate-co-ethyleneglycol dimethacrylate) interpenetrating polymer networks [PU/P (MMA–co–EGDMA)-IPNs] were synthesized and used as adhesives to adhere vulcanized natural rubber (NR) and soft polyvinyl chloride (PVC). The structure and morphology of the IPN adhesives in bulk and near the adhesive/substrate interfaces were investigated. A new mechanism of adhesion called conjugate interpenetration of networks across interfaces, which is suitable for IPN adhesives and polymer substrates, was put forward. According to this mechanism, while forming simultaneous interpenetrating networks in the adhesive, the monomers in the IPN adhesive can permeate polymer substrates and polymerize in situ to form gradient IPNs, thereby producing conjugate three-component IPNs near the adhesive/substrate interfaces. It is the conjugate interpenetration of the networks across the interfaces that strengthens interfacial combination remarkably and results in high bond strength of IPN adhesives. © 1994 John Wiley & Sons, Inc.     

木质素活化及在木材胶粘剂中的应用进展

木质素是相对分子量较高的天然聚合物,由于具有苯酚结构利于制备木材胶粘剂,但是木质素本身反应活性低,一般都将其活化后再利用.而且,除了以往利用最多的造纸工业产生的木质素外,研究发现木材经过褐腐菌降解后残留主要成分是结构部分发生变化的木质素,这种可再生生物质资源以其自身的结构特点在合成胶粘剂上也有很大的优势,本文结合木质素胶粘剂应用中的问题,重点概述了活化木质素的各种方法及褐腐木质素在木材胶粘剂中的应用.     

Effect of Lignin Structure Characteristics on the Performance of Lignin Based Phenol Formaldehyde Adhesives

As the second most abundant biopolymer, lignin remains underutilized in various industrial applications. Various forms of lignin generated from different methods affect its physical and chemical properties to a certain extent. To promote the broader commercial utilization of currently available industrial lignins, lignin sulfonate (SL), kraft lignin (KL), and organosolv lignin (OL) are utilized to partially replace phenol in the synthesis of phenol formaldehyde (PF) adhesives. The impact of lignin production process on the effectiveness of lignin-based phenolic (LPF) adhesives is examined based on the structural analysis of the selected industrial lignin. The results show that OL has more phenolic hydroxyl groups, lower molecular weight, and greater number of reactive sites than the other two types of lignins. The maximum replacement rate of phenol by OL reaches 70% w/w, resulting in organosolv lignin phenolic (OLPF) adhesives with a viscosity of 960 mPa·s, a minimal free formaldehyde content of 0.157%, and a shear strength of 1.84 MPa. It exhibits better performance compared with the other two types of lignin-based adhesives and meets the requirements of national standards.     

Miscibility and enzymatic degradation studies of poly(ε-caprolactone)/poly(propylene succinate) blends

In the present study the miscibility behaviour and the biodegradability of poly(ε-caprolactone)/poly(propylene succinate) (PCL/PPSu) blends were investigated. Both of these aliphatic polyesters were laboratory synthesized. For the polymer characterization DSC, ¹H NMR, WAXD and molecular weight measurements were performed. Blends of the polymers with compositions 90/10, 80/20, 70/30 and 60/40 w/w were prepared by solution-casting. DSC analysis of the prepared blends indicated only a very limited miscibility in the melt phase since the polymer-polymer interaction parameter χ₁₂ was −0.11. In the case of crystallized specimens two distinct phases existed in all studied compositions as it was found by SEM micrographs and the particle size distribution of PPSu dispersed phase increased with increasing PPSu content. Enzymatic hydrolysis for several days of the prepared blends was performed using Rhizopus delemar lipase at pH 7.2 and 30 °C. SEM micrographs of thin film surfaces revealed that hydrolysis affected mainly the PPSu polymer as well as the amorphous phase of PCL. For all polymer blends an increase of the melting temperatures and the heat of fusions was recorded after the hydrolysis. The biodegradation rates as expressed in terms of weight loss were faster for the blends with higher PPSu content. Finally, a simple theoretical kinetic model was developed to describe the enzymatic hydrolysis of the blends and the Michaelis-Menten parameters were estimated.     

Characterization of milled wood lignin and ethanol organosolv lignin from miscanthus

Ethanol organosolv lignin extracted from Miscanthus × giganteus (using the following conditions: T = 190 °C, t = 60 min, sulfuric acid = 1.2% w/w, EtOH/H₂O = 0.65) and milled wood lignin from Miscanthus × giganteus were subjected to a comprehensive structural characterization by ¹³C, ³¹P NMR, FTIR, UV spectroscopies and size exclusion chromatography. The results showed that Miscanthus lignin is an H/G/S type (4%, 52%, 44% respectively) with ∼0.41 β-O-4 linkage per aromatic ring and contains coumarylate linkages (0.1/Ar). It was shown that during organosolv treatment, cleavage of β-O-4 linkages and of ester bond (acetyl and coumaryl residues) was the major mechanisms of lignin breakdown but the process did not significantly change the core of the lignin structure.     

Polyurethane (urea)/polyacrylates interpenetrating polymer network (IPN) adhesives for low surface energy materials

On the basis of the polymerization of the acrylate phase catalyzed by the oxidation of trialkylborane at room temperature, a series of polyurethane (urea)/polyacrylates adhesives with interpenetrating polymer network structure (IPNS) was synthesized. The crosslinking polyurethane (urea) phase was synthesized by the reaction between polymer diamine or triol and isocyanate. The resulting IPN adhesives as a function of the polyurethane (urea) or 2‐hydroxylethyl acrylate terminated polyurethane (HEA‐PU) (crosslinking agent of acrylate phase) content were explored. The adhesive morphology took on the IPNS that manifested as a finely dispersed polyurethane (urea) phase in the acrylate phase. Excellent adhesion to low surface energy materials was achieved within a wide range of polyurethane (urea) contents. The IPN adhesives also displayed better flexibility than polyacrylate adhesives with HEA‐PU as a crosslinking agent. Copyright © 2011 John Wiley & Sons, Ltd.     

Phase Behavior of Polymer Blends

The present report deals with some results on phase behavior, miscibility and phase separation for several polymer blends casting from solutions. These blends are grouped as the amorphous polymer blends, blends containing a crystalline polymer or two crystalline polymers. The blends of PMMA/PVAc were miscible and underwent phase separation at elevated temperature, exhibited LCST behavior. The benzoylated PPO has both UCST and LCST nature. For the systems composed of crystalline polymer poly(ethylene oxide) and amorphous polyurethane, of two crystalline polymers poly(-caprolactone) and poly[3,3,-bis-(chloromethyl) oxetane], appear a single T_g, indicating these blends are miscible. The interaction parameter B's were determined to be –14 J cm^–3, –15 J cm^–3 respectively. Phase separation of phenolphthalein poly(ether ether sulfone)/PEO blends were discussed in terms of thermal properties, such as their melting and crystallization behavior.This revised version was published online in November 2005 with corrections to the Cover Date.     

Preparation of a blocked isocyanate compound and its grafting onto styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer

The ε-caprolactam was used to block the isocyanate group to enhance the storage stability of allyl (3-isocyanate-4-tolyl) carbamate. The spectra of FTIR and NMR showed that blocked allyl (3-isocyanate-4-tolyl) carbamate (BTAI) possesses two chemical functions, an 1-olefin double bond and a blocked isocyanate group. The FTIR spectrum showed BTAI could regenerate isocyanate group at elevated temperature. DSC and TG/DTA indicated the minimal dissociation temperature was about 135 °C and the maximal dissociation rate appeared at 226 °C. Then the styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS) was functionalized by BTAI via melt free radical grafting. The effect of temperature, monomer and initiator concentrations on the grafting degree and grafting efficiency was evaluated. The highest grafting degree was obtained at 200 °C. The grafting degree and grafting efficiency increased with the enhanced concentration of BTAI or initiator. The weight-average molecular weight (M_w) increased greatly at higher initiator concentration and lower ratio of the monomer/initiator. And the molecule weight distribution (MWD) of the modified SEBS became wider than that of pure SEBS. It is obvious that shearing thinning behavior of grafted SEBS is more profound than pure SEBS.     

Chemical synthesis of beta-O-4 type artificial lignin

An artificial lignin polymer containing only the beta-O-4 substructure was synthesized. The procedure consists of two key steps: 1) polycondensation of a brominated monomer by aromatic Williamson reaction; and 2) subsequent reduction of the carbonyl polymer. 13C-NMR and HMQC spectra of the polymer were consistent with beta-O-4 substructures in milled wood lignin isolated from Japanese fir wood. The weight average degree of polymerization (DP(w)) ranged from 19.5 to 30.6, which is comparable to enzymatically synthesized artificial lignin from p-hydroxycinnamyl alcohols (dehydrogenation polymer, DHP) and some isolated lignins. Using this new lignin model polymer, it will now be possible to reinvestigate the properties and reactivity of the main lignin structure in terms of its polymeric character.     

A study of the properties of a composite asphalt binder using liquid products of wood fast pyrolysis

The results of a study of the adhesive properties of a composite asphalt binder modified with pyrolytic lignin—a water-insoluble fraction of liquid products of fast pyrolysis of wood—are presented. It is shown that 10 wt % pyrolytic lignin increases the adhesive strength of the composite asphalt binder and the obtained samples of modified asphalt concrete correspond to the requirements of GOST (State Standard) 9128–84.     

Lignin and Lignin-Derived Compounds for Wood Applications—A Review

Improving the environmental performance of resins in wood treatment by using renewable chemicals has been a topic of interest for a long time. At the same time, lignin, the second most abundant biomass on earth, is produced in large scale as a side product and mainly used energetically. The use of lignin in wood adhesives or for wood modification has received a lot of scientific attention. Despite this, there are only few lignin-derived wood products commercially available. This review provides a summary of the research on lignin application in wood adhesives, as well as for wood modification. The research on the use of uncleaved lignin and of cleavage products of lignin is reviewed. Finally, the current state of the art of commercialization of lignin-derived wood products is presented.     

Effect of chemical structure of acrylic pressure‐sensitive adhesives for polarizing film on light leakage phenomenon in TFT‐LCDs

Increasing image quality in thin‐film transistor liquid crystal displays (TFT‐LCD) is a recognized challenge for electronic companies and specialists working in this area. One of the main problems in TFT‐LCDs is a phenomenon called “light leakage”, affecting black–white contrast and color brightness. It occurs because of a heat‐induced shrinkage and disorientation of the polarizing film of TFT‐LCD, which controls the intensity of the light from the backlight unit. Improvement of the light leakage can be achieved through using a pressure‐sensitive adhesive (PSA) used for assembling the polarizing film onto the TFT‐LCD panel. In this paper, eight acrylic/methacrylic monomers with high glass transition temperature (Tg) were employed for synthesis of the polymers for the adhesive. Effect of structure, Tg, and elasticity modulus of the synthesized polymers on the light leakage was investigated simultaneously for 2.5‐ and 7.0‐in. size samples. We demonstrated that the light leakage can be minimized through two different mechanisms—high stress relaxation of the polymers with low Tg and low modulus and high shrinkage resistance of the polymers with high Tg and high modulus. The results of this work indicate a possibility to develop a universal PSA for polarizing film in TFT‐LCDs of different sizes that will have a positive effect on manufacturing productivity and lowering prices of digital devices. Copyright © 2011 John Wiley & Sons, Ltd.