Novel, water-based fluorinated polymers with excellent antigraffiti properties

In this article we describe novel, water-based, crosslinkable fluorinated polymers that form coatings with excellent antigraffiti properties. The synthesis of the binders and the surface and bulk properties of their coatings are discussed. The surface properties of these coatings are characterized in terms of their surface-free energy, as calculated from static contact angle measurements. The distribution of the fluorine atoms throughout the coating is measured by X-ray photoelectron spectroscopy (XPS). The bulk properties are studied by determining the crosslink density through dynamic mechanical thermal analysis (DMTA), and the effect of the crosslinking conditions on the crosslink density and the antigraffiti properties is discussed. The results indicate that a combined action of surface and bulk properties gives these coatings their excellent antigraffiti properties. The applicability of these polymers as protective coatings for metal and concrete surfaces are demonstrated. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL     

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.     

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。     

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.     

ACR—g—VC共聚物的合成与性能研究

由两步乳液聚合合成了核－壳结构型ACR胶乳,并进一步通过ACR胶乳存在下的VC悬浮聚合合成ACR－g-VC共聚物,对接枝共聚物的结构和性能进行表征。结果表明：ACR胶乳的存在影响VC悬乳聚合的稳定性,增加分散剂用量能得到颗粒特性较好的共聚树脂;ACR－g-VC共聚物的溶胶聚合度略低于相同聚合温度的均聚PVC,凝胶含量随共聚组成中ACR含量的增加而增加;ACR－g-VC共聚物的塑化时间小于聚合度接近的均聚PVC,而加工转矩大于均聚ACR－g-VC共聚物的冲击强度随ACR含量的增加而增大,且大于ACR含量相当的PVC／ACR共混物。     

Structural methacrylate/epoxy based adhesives for aluminIum joints

The aim of this work was to investigate the influence of elastomer and monomer concentration on the properties of methacrylate/epoxy based adhesive formulations using a Plackett-Burman experimental design. The adhesive formulations were developed in order to bond non-treated aluminium panels. Their chemical structure was analysed by Fourier transformed infrared spectroscopy (FTIR) and the thermal behaviour by thermogravimetry (TGA) and differential scanning calorimetry (DSC) in comparison to a commercial adhesive. After room temperature mixing, time and temperature of the curing reaction were measured. Further, non-treated aluminium single-lap joints were adhesively bonded and their shear strengths were evaluated. The formulations showed chemical structure similar to a commercial adhesive but the thermal behaviour was quite distinct. The commercial adhesive cured slower than the developed adhesive formulations which can directly affect the bonding quality. However, some formulations showed higher shear strengths than the commercial one, but all with adhesive failure mode. The adhesive formulations with elastomers in methacrylate part showed the highest shear strengths.     

Influence of a wollastonite microfiller and a halloysite nanofiller on properties of thermally curable pressure-sensitive structural adhesives

A thermally curable pressure-sensitive structural tape (SAT-0) was prepared using an epoxy acrylate copolymer and an epoxy resin and modified with a wollastonite microfiller (SAT-W) and a halloysite nanofiller (SAT-H). Influence of the minerals on self-adhesive features and curing behavior of the tapes as well as on shear strength of aluminum/SAT/aluminum joints has been investigated. Thermally uncured SATs containing the fillers exhibited higher T_g (+5 °C for SAT-H), adhesion (+64% for SAT-H) and tack (+10% for SAT-W) while their cohesion was lower (−22% for SAT-W and −86% for SAT-H) in relation to SAT-0. Moreover, filler addition reduced the shear strength of the Al/SAT/Al overlap joints (−6% for Al/SAT-H/Al and −22% for Al/SAT-W/Al), however, the microfiller-based systems exhibited better crack and fatigue resistance, and higher shear strength after ageing tests than SAT-0 and SAT-H (+100% after thermal ageing, +85% after exposure in a climatic chamber, and +27% after immersion in a fuel).     

Van Der Waals Attraction Between Macroscopic Bodies

A general dispersion formula is derived, which represents the dispersion energy between two bodies A and B by their macroscopic screened fluctuation fields. These fluctuation fields are calculated exactly in the case of half-spaces and spheres. In the case of half-spaces the Lifshitz dispersion formula is obtained. The dispersion energy between spheres is found to vary as 1/d for separations d small compared with the radii and to be proportional to 1/d ⁶ for separations d large compared with the radii. The effect of layers adsorbed on the surfaces of the spheres on the dispersion energy is calculated. The dielectric properties of the adsorbed layers predominate over those of the bulk material for separations d smaller than the layer thickness.     

Lewis Pair Polymerization of Acrylic Monomers by N-Heterocyclic Carbenes and B(C6F5)3

This work has uncovered the first highly active and efficient Lewis pair polymerization (LPP) system based on N-heterocyclic carbene (NHC)/B(C₆F₅)₃ pairs for converting acrylic monomers into medium- to high-molecular weight polymers. The study has systematically examined steric and electronic effects of three 1,3-dialkyl(Me, ⁱPr, ^tBu)imidazol-2-ylidene NHCs on the LPP of three classes of acrylic monomers, including linear methyl methacrylate (MMA), cyclic biorenewable γ-methyl-α-methylene-γ-butyrolactone (_γMMBL), and difunctional allyl methacrylate (AMA). For MMA polymerization, IⁱPr is not only the most active (∼3× and ∼120× more active than IMe and I^tBu, respectively), but also the most effective NHC, especially under low NHC loading conditions. Kinetic results are consistent with a bimolecular, activated monomer propagation mechanism. In the case of the more reactive _γMMBL, the polymerization by NHC/B(C₆F₅)₃ in CH₂Cl₂ is extremely rapid, with all three NHCs achieving quantitative monomer conversion in 1 min and thus reaching a high turnover frequency of≥48,000 h⁻¹. The molecular weight (MW) of P_γMMBL can be tuned by adjusting the [_γMMBL]/[NHC] ratio, and thus high MW polymers with relatively narrow MW distributions can be readily synthesized (e.g., from M_n=1.41×10⁵ g mol⁻¹, Đ=1.08 to M_n=4.89×10⁵ g mol⁻¹, Đ=1.20). The LPP by NHC/B(C₆F₅)₃ is completely chemoselective, as demonstrated by the polymerization of AMA, which selectively polymerizes the conjugated vinyl group while leaving the non-conjugated vinyl group in the allyl moiety intact, thanks to its activated monomer propagation mechanism. The resulting PAMA is syndiotactic (rr=83 %), uncross-linked, and soluble in common solvents, thus suitable for further functionalization. This quantitatively chemoselective polymerization by NHC/B(C₆F₅)₃ should provide a facile, yet powerful, approach to functional acrylic polymers.     

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.