Facile preparation and strong adhesive strength of honeycomb polyurethane films with small pore diameter

With the continuous development of bionics, such as, geckos and virginia creeper with both superhydrophobic and super-adhesive, the surface wetting and super-adhesive properties of various porous materials have attracted extensive attention of the scientific and medical communities. Here, the honeycomb polyurethane (PU) porous films with strong adhesion were successfully prepared by microphase separation method and the effects of growth parameters on their microstructure and adhesive strength to ice were investigated. It was found that a high relative humidity (e.g., 100%) and a low solution concentration (e.g., 2%) facilitated the formation of ordered honeycomb PU porous films, and as-prepared PU pores with average pore diameter as small as 5 μm are better ordered and more uniform than these in related documents. Although the contact angle of water droplets on the surface of PU porous films increased from the premodification value of 85–130° to more than 160° after surface modification with polydopamine (PDA), the corresponding rolling angle remained approximately constant (180°), indicating that the surface of PU porous films has strong adhesion similar to geckos and virginia creeper. Furthermore, at lower temperature, the PU porous films exhibited the high adhesive strength of 142.13 kPa on ice, which was strongly dependent on the porous microstructures and surface compositions. The improved adhesive behavior to ice of honeycomb PU porous films modified with PDA provides new strategies for surface modification of materials and potential applications in medical domain.     

Recycling of multilayer packaging using a reversible cross-linking adhesive

Plastic-based multilayer packaging has an important function on the packaging market, but is currently not recyclable as the polymer layers used are usually thermodynamically immiscible. This work therefore follows the approach to prepare separable multilayer packaging using a packaging adhesive modified with thermally unstable adducts, and proposes a corresponding recycling process. For this purpose, typical multilayer structures (polyethylene (PE)// polyethylene terephtalate (PET), PET//aluminum, and PE//aluminum) were prepared by curing furan-/maleimide-functionalized polyurethane (PU)-prepolymers with a three-functional cross-linking agent. Adhesions of up to over 3N per 15 mm test specimen were measured or substrate failures of PET films were observed. However, heating in dimethylsulfoxide, the retro-Diels–Alder reaction takes place and the cross-linked adhesive turns thermoplastic and dissolves in the solvent. Thus, the laminate separates and the pure PE, PET, and aluminum foils can be recovered without any PU residue.     

Failure mode transition and energy dissipation in naturally occurring composites

The microstructural aspects of compressive inelastic deformation in balsa wood are investigated with emphasis on the failure mode transition and its effects on energy dissipation characteristics. The architectural features as well as the composite character of cell wall ultrastructure are discussed in a framework to understand the complex interrelationship between microstructure and macroscopic behavior in this extremely lightweight cellular biocomposite. Based on this discussion and experimental results, it is concluded that the biomimetic approach may prove to be a viable strategy in designing composite structures with high specific energy absorption capacity.     

Recent advances in isotropic conductive adhesives for electronics packaging applications

Isotropic conductive adhesives (ICAs) have recently received a lot of focus and attention from the researchers in electronics industry as a potential substitute to lead-bearing solders. Numerous studies have shown that ICAs possess many advantages over conventional soldering such as environmental friendliness, finer pitch printing, lower temperature processing and more flexible and simpler processing. However, complete replacement of soldering by ICAs is yet not possible owing to several limitations of ICAs which are mainly related to reliability aspects like limited impact resistance, unstable contact resistance, low adhesion and conductivity etc. Continued efforts for last 15 years have resulted in development of ICAs with improved properties. This review article is aimed at providing a better understanding of ICAs, their principles, performance and significant research and development work addressing the technological utility of ICAs.     

The concept of an endurance limit for adhesive joints

The effect of cyclic stressing on the strength of single lap adhesive joints has been studied and a considerable reduction in strength observed when the maximum stress exceeds about 40% of the ultimate tensile strength, but whether or not a true endurance limit exists is not proven. Fallacies are shown in some of the techniques which have been proposed for studying the fatigue behaviour of adhesive joints.     

结构粘结剂的试验研究

粘结剂是粘钢加固技术的关键材料,通过对粘结剂的试验研究,得到了粘结剂的拉压试验曲线与材料力学指标以及粘附于各种标号混凝土时,粘结层的抗剪强度;并且还进行了粘结剂的短期流变试验。     

A Mass Transport Model for Drying Wood under Isothermal Conditions

Mass transport in wood during drying can have different mechanisms at different periods of drying. Depending on the current moisture content (MC) and the structure of the wood, the driving forces for the mass transport are essentially different. Above the fiber saturation point (FSP), the lumens are partially saturated and the transport of liquid (free) water occurs as a consequence of capillary action. On the other hand, below the FSP, bound water within the cell walls is conveyed by diffusion, and water vapor in the lumens moves under influence of pressures gradient. Based on these considerations, a unified model is presented that takes into account the transport of the different moisture phases. Simulation of the drying of a Norway spruce sample at 50°C from about 135 to 7% MC is carried out using the finite element method (FEM). Comparison between the simulated average MC and the experimental observations obtained from X-ray computed tomography (CT) shows reasonable agreement. Possible simplifications in the model are briefly discussed as well as some aspects of the numerical implementation. Finally, the influence of absolute permeability on the average MC is studied.     

Energy Saving in Industrial Wood Drying Addressed by a Multiscale Computational Model: Board, Stack, and Kiln

This article proposes a multiscale computational model able to calculate energy consumption in a batch lumber kiln. A dual-scale computational model of wood drying deals with the boards/stack interaction and serves as a basis for the present work. A new module was added here that calculates heat losses through kiln walls (convection, condensation) and the energy used by each kiln component (fans, heating elements, humidifier, vacuum pump, etc.). The corresponding mathematical formulation is presented and then theoretical results are compared to those collected in an industrial vacuum kiln. As application example, the effect of air reversal, air velocity, and kiln insulation are exhibited, which depicts the great potential and prospects of this new tool for energy savings in relation to the product quality.     

Water‐soluble/dispersible cationic pressure‐sensitive adhesives. I. Adhesives from solution polymerization

Pressure‐sensitive adhesives (PSAs) have long been a problem as sticky contaminants for paper recycling mills. The main problem associated with such stickies is that the PSAs in the waste papers deposit on the felts, press rolls, and drying cylinders of paper machines, and this creates problems with paper formation, reducing the paper quality and paper machine runnability. The annual cost of stickies to the U.S. paper industry is estimated to be about $600,000,000–650,000,000. To solve this problem, a series of cationic water‐soluble/dispersible PSAs have been synthesized by the free‐radical solution polymerization of butyl acrylate and [3‐(methacryloylamino)propyl]trimethylammonium chloride in ethanol. The PSA end‐use properties, repulpability in paper recycling, and the effects on the properties of recycled paper products have been studied. The cationic PSAs can be dissolved or dispersed in water if the cationic charge density in the PSA backbone is controlled, and so they do not deposit as stickies during recycling and papermaking processes. Because the PSAs are cationically charged, they can easily be removed from the papermaking system by adsorption onto the negatively charged fibers and fine surfaces. Furthermore, the adsorbed colloidal or dissolved PSAs have little effect on the final paper properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1624–1630, 2003