Лако-красочные материалы — производство

The fracture toughness of wood in terms of crack initiation energy ranges from 50 to 1000 J/m2, whereas the crack initiation energies for typical thermosetting polymers are in the range 100 to 300 J/m2 [27]. It seems interesting that wood joints bonded with conven­tional thermosetting adhesive also have fracture toughness values of about 100 to […]

A. Wood Since wood fracture usually dominates the performance of well-made joints, it is worth­while before focusing on the bonded joint and the influence of the adhesive to examine how wood itself fractures. At the molecular level, Porter [19] found that wood fractures in the amorphous, water-accessible regions of the cell wall rather than in […]

Bryan H. River Forest Products Laboratory, USDA-Forest Service, Madison, Wisconsin, U. S.A. I. INTRODUCTION Adhesives are arguably the most important fastening system used with forest products. Large volumes of adhesives are used successfully in wood-, particle-, and fiber-based industries. In fact, large and important industries such as panel products would not exist without adhesives. However, […]

As mentioned earlier, the DMTA technique measures molecular motion in adhesives, and not heat changes as with DSC. Many adhesives exhibit time-dependent, reversible visco­elastic properties in deformation. Hence a viscoelactic material can be characterized by measuring its elastic modulus as a function of temperature. The modulus depends both on the method and the time of […]

Quantitative results can be obtained by converting the sample compartment of a DTA apparatus into a differential calorimeter. The instrument, a differential scanning calori­meter, is built based on this principle. In this setup, the sample and reference are heated directly with separate heating coils as shown in Fig. 21. A heating coil makes the tem­perature […]

Heat or temperature has a considerable effect on curing, working life, and stability of adhesives. Several structural transitions can occur in adhesives during heating. Thermal analysis techniques can provide a detail road map of curing, properties, and stability of cured adhesives that has predictive utility. They also provide the ability to assess degree of cure […]

Nuclear magnetic resonance (NMR) spectroscopy is now well established as one of the most useful instrumental techniques for characterization of adhesives and for the study of polymeric adhesive structure-property relationships [34]. The reasons are that (1) indivi­dual chemical groups in adhesive often give signals that can be resolved, (2) the NMR signals are sensitive to […]

Vibrational spectroscopy has been widely used to identify polymers, to quantitatively analyze chemical composition, and to specify configuration, conformation, branching, end groups, and crystallinity. Chemical reactions including polymerization, curing, cross­linking, degradation, and weathering have been studied using vibrational techniques. Light, which is a form of electromagnetic radiation, can interact with matter in a number of […]

The technique of GPC or SEC is introduced for determination of the molecular weight and MWD of adhesive polymers, separation of small molecules, and preparation of mole­cular weight fractions. This technique is possibly the most widely used chromatographic technique in polymer analysis. It is capable of characterizing very high-molecular-weight polymers up to 106, thermoset resins […]

The molecular weight of an adhesive is of prime importance in its preparation, application, and performance. The effect of molecular weight on the tensile strength or bonding power of an adhesive is illustrated in Fig. 1. At very low molecular weights, the ultimate tensile stress is near zero. As the molecular weight increases, the tensile […]