Natural weathering performance of exterior wood coatings on <Emphasis Type="Italic">pinus sylvestris</Emphasis> and <Emphasis Type="Italic">pinus radiata</Emphasis> in Germany and New Zealand

The weathering of commercial coatings on pine sapwood in Germany and New Zealand was studied. The New Zealand site had a climatic index 50% more challenging. Significant differences in performance relating to coating, species, site, and exposure are presented. The coating and site had the most significant effects, while species had the least. A solvent-borne stain and a hybrid paint qualified for stable end-use situations in both countries. An acrylic paint performed better in Germany while an alkyd gave the poorest performance of the four coatings tested. More effective fungicidal coating preperties are required in New Zealand to suppress mold growth. Areas of deficiency for internationalizing the European weathering standard EN 927 are discussed.     

Preparation of polymerizable miniemulsions by ultrasonication

Styrene miniemulsions are prepared by ultrasonicating a system at different amplitudes until an equilibrium is reached. It is shown by turbidity measurements that the efficiency of the dispersion process is strongly dependent upon the ultrasonication time at the different amplitudes. In addition, the influence of monomer type on the homogenization process is also shown. The sizes of the droplets (before and after polymerization of the particles) are mainly determined by the type of monomer as well as the type and amount of the surfactants, as is shown for methyl methacrylate and butyl acrylate as monomers.     

Preparation of an acrylic‐grafted polyester and its aqueous dispersion—Effect of the molecular structures of the grafted polyesters on viscosity and rheology of dispersion

An investigation was undertaken to develop a new class of water‐borne polyesters that have various viscosity and various rheological profiles. We discussed the effect of the grafting condition on the molecular weights of the acrylic segments in the acrylic‐grafted polyester. The molecular weights of the acrylic segments could be changed by an initiator concentration, a chain transfer agent concentration, and a monomer concentration. We discussed the viscosity and the rheology of the dispersions obtained from the above‐grafted polyesters. The viscosity of the dispersion decreased as the molecular weights of the acrylic segments decreased. It was considered that the interaction between the particles of the dispersions decreased with a decrease in the thickness of the shell layer. The viscosity of the dispersions also decreased as the solubility of the acrylic segments in water decreased. It was considered that the interaction between the particle of dispersion decreased with the shrinkage of the shell layer. The rheological profile of dispersion was changed not by the molecular weights but the composition of the acrylic segments. The dispersions having various rheological profiles could be obtained by the control of the molecular weights or the composition of the acrylic segments in the grafted polyesters. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 350–356, 2000     

Design of adhesive joints based on peak elastic stresses

The paper is focused on the static strength of adhesively bonded structural joints and seeks a simple calculation rule that can assist the designer in everyday engineering practice. The work encompasses three steps. In the first step, an experimental campaign is carried out on an assortment of customized bonded joints (single lap and T-peel) made of steel strips bonded by an acrylic structural adhesive. The dimensions of the joints are chosen so as to produce a wide range of combinations of shear and peel stresses in the adhesive layer. In the second step, the stress analysis of the joints is performed by means of a sandwich model that describes the variability of shear and peel stresses over the overlap length but disregards the stress singularities at the corners. In the third step, a design rule is inferred by noting that, in a chart having as axes the peak values of the peel and shear components in the adhesive at failure, the points—calculated for each joint at the 2% (deviation from linearity) proof load—define a limit zone. The inferred design rule is that the adhesive withstands the load if the representative point of the stress state lies inside this zone. For the tested case, the envelope of the limit zone has an approximately rectangular shape. This criterion predicts the failure load of the joints far better than the simplistic approach based on the nominal stress calculated as the ratio of the load to the bonded area.The paper also discusses the response which is obtained by applying, to the same experimental data, the traditional calculation based on the mean stress (force to area ratio), and the more sophisticated approach based on the stress intensity factor, which accounts for the singularity of the stress field. Applied to our experimental data, the performance of both has been unsatisfactory.     

Shear strength of adhesively bonded polyolefins with minimal surface preparation

Interest in polyethylene and polypropylene bonding has increased in the last years. However, adhesive joints with adherends which are of low surface energy and which are chemically inert present several difficulties. Generally, their high degree of chemical resistance to solvents and dissimilar solubility parameters limit the usefulness of solvent bonding as a viable assembly technique. One successful approach to adhesive bonding of these materials involves proper selection of surface pre-treatment prior to bonding. With the correct pre-treatment it is possible to glue these materials with one or more of several adhesives required by the applications involved. A second approach is the use of adhesives without surface pre-treatment, such as hot melts, high tack pressure-sensitive adhesives, solvent-based specialty adhesives and, more recently, structural acrylic adhesives as such 3M DP-8005^® and Loctite 3030^®.In this paper, the shear strengths of two acrylic adhesives were evaluated using the lap shear test method ASTM D3163 and the block shear test method ASTM D4501. Two different industrial polyolefins (polyethylene and polypropylene) were used for adherends. However, the focus of this study was to measure the shear strength of polyethylene joints with acrylic adhesives. The effect of abrasion was also studied. Some test specimens were manually abraded using 180 and 320 grade abrasive paper. An additional goal of this work was to examine the effect of temperature and moisture on mechanical strength of adhesive joints.     

可见光固化树脂的固化性能的研究

研究了在532nm激光条件下,环氧丙烯酸树脂的光固化过程。实验表明：光引发剂质量分数为4％时,临界曝光量Ec最小;随着叔胺质量分数的和有机色素质量分数的增加,临界曝光量逐渐增加;激光能量越大,临界曝光量越小,激光能量大于400mW时,激光能量增加对临界曝光量几乎无影响。