Associative polymer/latex dispersion phase diagrams II: HASE thickeners

The colloidal interactions of HASE associative polymers and latexes in the presence of surfactant are complicated and subject to a number of variables. Both bridging and depletion flocculation can occur, in addition to good particle dispersion. Dispersion phase diagrams have been developed to help visualize these interactions. The various dispersion states can have a significant effect on coating formulations and film properties. Examples of dispersion phase diagrams are presented for a model HASE anionic associative thickener and various model latexes in the presence of sodium dodecyl-sulfate and nonionic surfactants. The major variables affecting dispersion behavior are associative polymer concentration, latex particle size, latex surface hydrophobicity, electrolyte concentration, and surfactant concentration. The dispersion phase behavior of the HASE systems is compared to that of HEUR thickened systems reported previously. A significant difference is that much less bridging flocculation is observed in the HASE systems. In addition, nonionic surfactants induced depletion flocculation in the HASE systems but not in the HEUR systems.     

Bring back the steel? The growth of plastics in automotive applications

The development of plastics has evolved from the use of natural materials to the use of chemically modified natural materials and, finally, to completely man-made molecules. Plastics continue to improve, to afford flexibility, high-impact, and strength. In automotive applications, plastics have increased in utilization to comprise approximately 10% of the total vehicle weight. They offer increased ductility, freedom from corrosion, and increased styling capability. Although plastics have had a remarkable impact on our culture, it is obvious that there is a price to be paid for their use. Plastics are almost too good, as they are durable when processed correctly, but easily damaged when utilized in the incorrect application. Plastics also degrade very slowly, making recycling mandatory. And finally, while plastics consume only 4% of the world’s oil production (petroleum is the raw material that is chemically altered to form commercial plastics), their cost hinges on the cost of petroleum. As petroleum prices increase, so too will the cost of plastic. In 2004, the higher price of plastic forced many plastic manufacturers out of business, and forced many automotive suppliers to look into alternative replacements. With publications such as USA Today reporting that current oil reserves will only last 40 years, scientists continue to seek cheaper alternatives to plastic. This article summarizes the history of commercial plastic development, with a focus on utilization of the materials in automotive applications. Damage criteria of plastic components, namely scratch, oxidative degradation, and impact, are discussed in relation to coatings and processing robustness. Environmental regulations, particularly in relation to recycling mandates, are explained. And finally, trends in alternative material development, including bioplastics, films, ceramic coatings, and nano-composites; are formulated. Presented at the 83rd Annual Meeting of the Federation of Societies for Coatings Technology, November 6–9, 2005 in Las Vegas, NV.     

Validation of the reciprocity law for coating photodegradation

Accelerating the photodegradation of commercial polymeric materials has great practical importance in the weathering community. However, questions exist as to whether high radiant flux exposure results can be extrapolated to in-service exposure levels. Based on the reciprocity law, the photoresponse of a material is dependent only on the total energy to which the specimen is exposed, and is independent of the exposure time and the intensity of the radiation taken separately. An experiment to validate the applicability of the reciprocity law for polymeric coatings has been carried out using the NIST integrating sphere-based ultraviolet (UV) weathering device. A nonpigmented, non-UV stabilized acrylicmelamine coating was exposed to six different UV radiation intensities ranging from 36 W/m² to 322 W/m², and in the spectral region between 290 nm and 400 nm. Chemical changes in the coating due to UV exposure were measured with transmission Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy. Using two dose-damage models, the reciprocity law photoresponse for this polymeric system was verified for different photodegradation mechanisms, including chain scission, oxidation, and mass loss. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL.     

Studies on thin film materials on acrylics for optical applications

Deposition of durable thin film coatings by vacuum evaporation on acrylic substrates for optical applications is a challenging job. Films crack upon deposition due to internal stresses and leads to performance degradation. In this investigation, we report the preparation and characterization of single and multi-layer films of TiO₂, CeO₂, Substance2 (E Merck, Germany), Al₂O₃, SiO₂ and MgF₂ by electron beam evaporation on both glass and PMMA substrates. Optical micrographs taken on single layer films deposited on PMMA substrates did not reveal any cracks. Cracks in films were observed on PMMA substrates when the substrate temperature exceeded 80°C. Antireflection coatings of 3 and 4 layers have been deposited and characterized. Antireflection coatings made on PMMA substrate using Substance2 (H2) and SiO₂ combination showed very fine cracks when observed under microscope. Optical performance of the coatings has been explained with the help of optical micrographs.     

Ageing of adhesively bonded joints—fracture and failure analysis using video imaging techniques

An investigation into the durability of adhesively bonded joints has been undertaken to help improve the prediction of joint lifetimes. Polymethylmethacrylate (PMMA) substrates have been bonded with a two-part acrylic adhesive to make single lap-shear joints. Joints have been aged in a hot/wet environment (40°C and 95% humidity) with no applied stress for up to 4000 h and were tested in tension. The novel aspect of the research has been the development of a video imaging analysis technique which allows damage initiation and propagation within the joint to be detected as load is applied to the joint. Images of fracture initiation and damage propagation have been correlated with stress/displacement data for joints under tensile loading. The data from aged samples is compared with data from un-aged samples. Both the stresses at which damage is seen to initiate and the final failure stress of the joints decrease as the ageing time increases. The failure mode changes from cohesive failure within the PMMA substrate to failure within the adhesive, near the PMMA/acrylic adhesive interface.     

Post-polymerization of waterborne alkyd/acrylics. Effect on polymer architecture and particle morphology

The limiting conversion commonly attained in the synthesis of waterborne alkyd/acrylic hybrid latexes hinders their industrialization. In this work, the mechanisms causing the limiting conversion were studied and post-polymerization conditions to efficiently remove the residual monomer determined. Further, it was observed that both the polymer architecture and the particle morphology were modified during post-polymerization. The mechanisms involved in the modification were investigated.     

Influence of Acrylic Adhesive Viscosity and Surface Roughness on the Properties of Adhesive Joint

In adhesion, the wetting process depends on three fundamental factors: the surface topography of the adherend, the viscosity of the adhesive, and the surface energy of both. The aim of this paper is to study the influence of viscosity and surface roughness on the wetting and their effect on the bond strength. For this purpose, an acrylic adhesive with different viscosities was synthesized and some properties, such as viscosity and surface tension, were studied before adhesive curing took place. Furthermore, the contact angle and the lap-shear strength were analyzed using aluminum adherends with two different roughnesses. Scanning electron microscopy was used to determine the effect of the viscosity and the roughness on the joint interface. The results showed that the adhesive exhibits an optimal value of viscosity. Below this value, at low viscosities, the low neoprene content produces poor bond strength due to the reduced toughness of the adhesive. Additionally, it also produces a high shrinkage during curing, which leads to the apparition of residual stresses that weakens the interfacial strength. However, once the optimum value, an increase in the viscosity produces a negative effect on the joint strength as a result of an important decrease in the wettability.     

Dehydrogenative Coupling of Poly(phenylsilane) by Metallocene Catalysis

The use of two different types of metallocene catalysts in the dehydrogenative coupling of phenylsilane to produce poly(phenylsilane) was investigated. The metallocene catalysts were first synthesized (i) through the reaction of zirconcene dichloride with n-butyllithium in toluene and (ii) through the reaction of zirconocene dichloride with sec-butyllithium in toluene. After the catalyst synthesis, phenylsilane was added in situ commencing polymerization of the phenylsilane to poly(phenylsilane) through dehydrogenative coupling in each case. The resulting poly(phenylsilanes) were characterized by ¹H NMR, GPC, FTIR, and UV/Vis, and were shown to be successful photoinitiators for a variety of acrylate and methacrylate type monomers.     

柔软型粘合剂的研制与应用

采用自由基乳液聚合工艺合成水性聚丙烯酸酯乳液，内乳化法合成水性聚氨酯预聚体，二者按一定比例共聚合成了柔软型涂料印花粘合剂．产品经测试，干摩擦牢度3．5—4．0级，湿摩擦牢度为3．5—4．0级．生产工艺简单，成本较低．     

丙烯酸酯微乳液的合成以及在皮革中的应用

本文以丙烯酸丁酯、甲基丙烯酸甲酯和丙烯酸为主要的共聚单体,十二烷基硫酸钠和反应型含双键的聚醚硫酸盐（NTS-10）为复合阴离子乳化剂,采用种子乳液聚合法合成了水性透明的丙烯酸酯微乳液。通过分析丙烯酸酯微乳液反应体系中各因素对乳液透明性、稳定性、黏度的影响,找出最佳的工艺条件。结果表明：当聚合反应温度为80℃,反应时间2h,m（BA）：m（MMA）=4：3,W（AAC）=3％,复合乳化剂中m（K-12）：m（NTS-10）=4：1,训（复合乳化剂）=10％时,该微乳液具有很好的透明性和稳定性,作为涂饰剂喷涂在皮革上,具有涂膜平整光亮,粘合牢固,渗透性强,能保持天然皮革透气透水性等特点。