Facile preparation of bimodal polyethylene with tunable molecular weight distribution from ethylene polymerization catalyzed by binary catalytic system in the presence of diethyl zinc

A series of novel honeycomb films of tri- and octa-arm polystyrene-b-poly(tert-butyl acrylate) star polymers prepared by atom transfer radical polymerization and nitroxide mediated radical polymerization, respectively, have been fabricated. The type of solvents, specifically their miscibility in water is one of essential parameters to construct ordered pore structures. The tri- and octa-arm star polymers yield well-ordered microporous film specifically in 10 to 30 g/L CHCl₃ solution. The contact angle of glass slide substrate (54.57°) is adjusted to 41.06° by plasma treatment and to 12.21° by coating the glass slide with highly hydrophilic hyperbranched polyglycidol. The ordered honeycomb films are created on the hydrophobic substrates, but the ordered films are not formed on the hydrophilic substrates. Microspheres with the diameters ranging from hundreds of nanometers to several micrometers are also obtained by a slight modification of breath figure method.     

Ice adhesion to rubber materials

The aim of this study was to investigate the interfacial shear strength between ice and rubbers. Different rubber materials containing only a polymer and curing agent (peroxide) were tested with regard to surface wettability and interfacial shear strength. The effect of different grades and amounts of carbon black filler was also studied. The wettability was determined from contact angles, using water and diiodomethane as test liquids, measured on carefully cleaned and mirror smooth rubber sheets. The test showed that there is a correlation between ice adhesion and rubber substrate wettability. Below a water contact angle of 90°, the interfacial shear strength of ice decreases linearly with increasing contact angle. For contact angles above 90°, the interfacial shear strength of ice stays practically the same. The presence of high surface energy additives such as reinforcing carbon black (e.g. N220 ISAF) significantly increases the interfacial shear strength. The highly hydrophobic behaviour of different plant surface textures was also investigated regarding ice adhesion strength. The combination of a submicrometer textured surface and a hydrophobic surface characteristic showed an abrupt decrease in the adhesion force of a water droplet at measured macroscopic contact angles above approximately 150°. Despite this water repellency, the ice adhesion strength is not nil. However, it was among the lowest values experienced in the test.     

Properties of composite films comprising surface modified fine collagen particles dispersed in polyurethane matrix

Collagen-rich natural leather powders (PPd) with average particle size of 12 μm were modified and dispersed in a polyurethane (PU) matrix. Three kinds of surface modification techniques were employed; surface polyaddition of PU, copolymerization with acrylamide (AAm), and grinding of the PPd with PU powder in a planetary ball mill. Surface modification was confirmed mainly by FTIR signals from the modifier. The DTA exothermic peak shifted toward a higher temperature by 260 K when copolymerized with AAm. On the copolymerized sample, the IR peak due to C(DOUBLE BOND)O stretching appeared between those of the original AAm and PPd, indicating the mutual chemical interaction. The tensile yield stress and critical strain of the composite films increased by surface modification with PU, while the latter decreased for the film containing the PPd powders copolymerized with AAm. Judging from the micrographs of the expanded films, the increase in the adhesive strength between the powder surface and the matrix after modification by AAm was larger than those by PU. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1693–1700, 1997     

Design factors for reducing ice adhesion

The purpose of this study was to investigate the relationships between a type of engineering material and the ice adhesion strength while in direct application in icing conditions. Ice adhesion tests were conducted on various materials with different surface conditions. There is an identified need for systematic studies on the effects of varying surface conditions with well-characterized roughness and accurate adhesion measurement. This information is key in understanding the adhering behaviour of ice which is a necessary prerequisite for modelling the behaviour of ice adhesion to other surfaces and for icing prevention. Results show that the type of material will determine, in large, the strength of the ice adhesion between surfaces with similar roughness characteristics and the receding contact angle of water can be used as a predictor of relative ice adhesion. The adhesive strength of ice can be increased or decreased dramatically by means of adjusting the surface roughness with a uniform process. Each material tested exhibits a similar linear relationship. There was a stark contrast in the ice adhesion between the varying materials despite very similar polished surface conditions and static water contact angles. Ice bonded to the glass surface with an adhesion of 1562 ± 113 kPa, and to aluminum at 1039 ± 117 kPa, and stainless steel at 1022 ± 115 kPa, and finally Teflon at only 33 ± 52 kPa and during 80% of trials the ice/substrate interface was broken with no measured adhesion. The information gathered can be used to improve designs for a number of devices needed in cold weather climates.     

Effects of wood-surface roughness,adhesive viscosity and processing pressure on adhesion strength of protein adhesive

The objective of this research was to study the effects of wood-surface roughness, adhesive viscosity and processing pressure on adhesion strength between soybean protein adhesive and wood, and to seek the relative importance of the individual factors in determining adhesion strength. Processing pressure was found to be the most important factor in determining adhesion strength. An optimum pressure, which was about 4.55 MPa in this research, is needed for development of a strong bond. A higher pressure resulted in reduced adhesion strength, possibly due to damage to the wood surface; a lower pressure also resulted in decreased adhesion strength because of the lack of bond formation. Adhesive viscosity had greater effect on adhesion strength than surface roughness. Contact angle, which was found to be mainly determined by adhesive viscosity and surface roughness, was a major factor controlling adhesive penetration. A smaller contact angle, resulting from lower viscosity and rougher surface, produced deeper penetration, while a larger contact angle, resulting from higher viscosity and smoother surface, produced shallower penetration. An optimum penetration is needed to enhance adhesion strength by developing a three-dimensional interactive zone at the interface. Too deep or too much penetration would result in 'dry-out' at the interface; less penetration would limit the formation of the three-dimensional zone at the interface. Both cases resulted in reduced adhesion strength. Contact angles ranging from 35 to 47° provided the optimum penetration needed for good adhesion. The results of this research could be used as reference to determine optimum process parameters in plywood manufacturing when an aqueous based adhesive is used.     

PDA/SiO2改性聚氨酯制备含结构色复合材料

采用改良St?ber法制得187、245、274 nm 3种粒径的SiO2微球，使用聚多巴胺（PDA）对SiO2微球进行包覆，制备了蓝色、绿色、红色3种不同颜色的非晶光子晶体PDA/SiO2（APCs）；将非晶光子晶体PDA/SiO2引入聚氨酯（PU）制得复合材料PDA/SiO2/PU 。利用FT-IR、CA、SEM、TEM、UV-Vis、DLS及万能试验机对PDA/SiO2及复合材料PDA/SiO2/PU的结构与性能进行表征分析。结果表明：APCs的颜色取决于SiO2微球的粒径；通过调节PDA的包覆量可调整APCs的色彩饱和度；APCs引入PU后可得到呈暗红结构色聚氨酯，其最大拉伸强度可达40.28 MPa，水接触角达113°，使得聚氨酯具有结构生色性和优异的机械性能与疏水性。     

Hydrophilic and hydrophobic poly(l‐lactic acid) films by building porous topological surfaces

Surface wettability of thin films is significant for their functional properties. Poly(l ‐lactic acid) (PLLA) is proposed as film matrix for building porous topological surfaces. By controlling the dope composition and ambient conditions, the films with ordered pores at micrometer scale are obtained. The results demonstrate that the hydrophilic or hydrophobic surface can be realized by building the porous topological surfaces. Increasing polymer concentration can lead to decreased pore size. The transition behavior of surface pores from discrete bowl‐like to interconnected honeycomb‐like structure with the increasing humidity is observed. The contact angle of top surface of film is higher than that of bottom surface, which verified the different roughness performance. The morphology and scale of topological structure are markedly related with the template effect of water droplets. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44572.     

Underwater polyurethane adhesive with enhanced cohesion by postcrosslinking of glycerol monomethacrylate

Polyurethane (PU) has been widely used as a glue in various areas. However, adhesion in the presence of water is greatly impeded and results in most synthetic adhesive failure. In this study, we designed and synthesized a novel PU construction; underwater PU adhesives were created by the incorporation of synthetic glycerol monomethacrylate (GMA). Furthermore, the urethane structure helped the adhesive eliminate the interfacial water barrier through interactions that were stronger than hydrogen bonding, and GMA as a crosslinking agent was used to generate post‐covalent‐crosslinking networks through radical polymerization. This enhanced the cohesion so the diffusion of water molecules could be overcome. Fourier transform infrared spectroscopy, thermogravimetric analysis, underwater adhesion measurements, and tensile tests were used to characterize the chemical and mechanical properties of the as‐obtained adhesive. This led to an adhesive with a better mechanical strength and interfacial adhesion in water, and the results show that the mechanical properties (tensile strength, Young's modulus, and tensile elongation) of the GMA–PU adhesive were higher than those of the pure PU. As for the 4% GMA, the tensile strength was enhanced by 24.3% and the elongation was enhanced by 125.23% over those of the pure PU. This confirmed that the incorporation of GMA into the PU matrix indeed induced increasing cohesion, and the sample's adhesive strength was 21.19 ± 3.9 MPa; this indicated a superior adhesive strength over that of the pure PU. In addition, we can foresee that underwater adhesion will play an important role in prospective surgery and engineering areas. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46579.     

Hemocompatibility evaluation of polyurethane film with surface‐grafted poly(ethylene glycol) and carboxymethyl‐chitosan

To improve the hemocompatibility and biocompatibility of polyurethanes (PUs), PU surface was firstly modified by poly(ethylene glycol) PEG through acryloyl chloride and subsequently grafted on carboxymethyl‐chitosan (CMCS). Attenuated total reflection Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy analysis confirmed that carboxyl‐chitosan was grafted onto PUs surface. The surface properties of unmodified and modified PU films were determined and compared by water contact angle assessment. After PEG and CMCS grafting, the surface energy of the PU film was increased. Furthermore, the hemocompatibility of the modified PU films was systematically evaluated by bovine serum albumin (BSA) adsorption, the dynamic blood clotting test, the platelet adhesion test, and the hemolytic test. It appears that BSA adsorption and platelet adhesion were significantly curtailed for the modified PU films. Therefore, the obtained results showed the modified PU film has better hemocompatibility. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Adhesive and repulsive properties of water droplet impact on honeycomb surfaces through breath figure method

The honeycomb porous films of tadpole‐shaped polyhedral oligomeric silsesquioxane fluorinated acrylates copolymers were fabricated through breath figure method. The static hydrophobic properties were studied through water contact angles (CAs) and the rim width/pore size (W/D) values. It was found that the low W/D value and high fluorine content generally indicated a high water CA. The properties such as morphology variations, energy conversion, contact diameter, adhesive, and repulsive forces were investigated on the porous and pincushion films. Furthermore, the kinetic energy of the droplet was converted into surface energy and internal energy dissipation after it impacted the surface. The residual energy made the droplet to recoil and influenced the bouncing height. The contact diameter and bouncing height characterized the energy level of the surface, and determined the surface energies of the copolymer/water/air system as well as the wettability. Finally, the adhesion and repulsion of water droplet on different surface at the times of establish contact, maximum contact diameter, and maximum bouncing height were compared. This work was helpful for us to further understand and control the adhesive force and the repulsive force on the porous and pincushion structure films. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45476.     

The influence of temperature and cyclic loading on adhesion in polycarbonate-polyurethane-glass adhesive joint

The paper deals with the influence of temperature and cyclic loading on adhesion and transparency of the adhesive joint consisting of soda-lime-silica glass and polycarbonate (PC) bonded with polyurethane (PU) adhesive film. The tested joint represents critical part of transparent armored glass used in vehicles. Dynamic tension creep tests were performed at temperatures to which armored glass is commonly exposed (25, 50, 60, 70, and 80?°C). Sawtooth loading mode was performed to 650?N and the sine loading in the force range 0–1550?N. The aim of the paper was to discover conditions causing delamination of the adhesive joint and glass milky appearance during the use. Delamination of soda-lime-silica glass/PU adhesive interface occurred at 25?°C after load to 1550?N without the change of transparency. Both dynamic and static tension creep tests performed to 400?N led to plastic deformation of PU adhesive at and above 70?°C, in preference at both ends and circumference edges of adhesive joint, and thus, to loss of transparency, but extent of deformation differed. Milky maps observed after sawtooth load to 650?N at 80?°C reflected delaminated areas of highly deformed PU adhesive. Temperature of 70?°C was found out to be the critical parameter being in synergy effect with different thermal expansion of PC and PU adhesive.     

Development of improved polypropylene adhesive bonding by abrasion and atmospheric plasma surface modifications

The present work deals with the problematic adhesive bonding of substrates with low surface energy. Different approaches have been explored with the aim of creating adequate adhesive joints based on polyolefinic substrate and polyurethane adhesive. The selected material under study was polypropylene (PP) as adherend, and a commercial Sikaflex^®-252 polyurethane one component based structural adhesive (PU) as joint fluid. Among the diverse pre-treatments typically used to prepare surfaces prior to bonding, mechanical abrasion with emery paper of 80 grain size, the use of a chemical primer and atmospheric pressure air plasma torch (APPT) were the selected methods to facilitate the application of the PU by means of surface energy enhancement as well as to create a correct mechanical interlocking of the adherent–adhesive interface. Changes in the wettability of the polymer were evaluated by contact angle measurements following the UNE EN 828:2010. Surface energy was calculated both in terms of Owens approximation and acid–base considerations, leading to the possibility of determining a relationship between changes in surface energy and adhesion. Changes in the chemical composition of the surface were studied by X-ray photoelectron spectroscopy (XPS), electron diffraction X-Ray (EDX) probe and attenuated total multiple reflection mode infrared spectroscopy (ATR-FTIR). Morphological modifications were investigated with scanning electron microscopy (SEM). Variations in the strength of single-lap PP–PP joints with the treatments were evaluated by lap shear tests following the UNE-EN 1465:2008 standard. Experimental evidence supports the superiority of the APPT treatment to increase wettability and adhesion of polyolefinic surfaces, especially when combined with the use of a primer.     

Some Effects of Corona Discharge Treatment of Biaxially-Oriented Polypropylene Film

The effects of the unit corona-treatment energy on the contact angle of various liquids, on the surface free energy, on the extent of oxidation of a surface layer, and on the adhesion of acrylic adhesive were studied using a biaxially-oriented polypropylene (BOPP) film. The surface free energy was determined with the van Oss-Chaudhury-Good (VCG) approach as well as with the wettability method. The extent of oxidation of the surface layer of the corona-treated BOPP film was evaluated with X-ray photoelectron spectroscopy. The adhesion strength of joints between the BOPP film and the acrylic adhesive was measured using the 180°-peel test.

In the range of the unit corona-treatment energy up to 1.2 kJ/m², a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.     

Improved adhesion of EVAs with different vinyl acetate contents treated with sulphuric acid

Four ethylene vinyl acetate copolymers (EVAs) containing 9, 12, 18 and 20 wt% vinyl acetate (VA) were treated with concentrated sulphuric acid to improve their adhesion to polychloroprene (PCP) adhesive. The tensile strength and Young's modulus of EVAs decreased as the VA content increased, due to the reduction in crystallinity of the polyethylene blocks in the copolymer. The modifications produced in the EVAs by treatment with sulphuric acid were followed using contact angle measurements (water, 25 °C), ATR-IR spectroscopy and scanning electron microscopy (SEM). Adhesive-bond strength was obtained by T-peel tests on treated EVA/polychloroprene adhesive joints. The vinyl acetate content in the EVA affected the extent, but not the nature, of the surface modification produced by treatment with sulphuric acid. The treatment produced both sulfonation and oxidation on the EVA surfaces. The higher the vinyl acetate content in the EVA, the more significant the modifications produced. Increased T-peel strengths of EVA/polychloroprene adhesive + 5 wt% polyisocyanate joints were obtained and a mixed failure (adhesion failure + cohesive failure in the adhesive) was produced. It was found that, to be effective, the treatment of EVAs must be carried out with 96 wt% sulphuric acid.     

Fabrication of biomimetic gecko toe pads and their characterization

The mimicking and fabrication of gecko toe pads structures can lead to limitless applications. In this study, polypropylene (PP), polyethylene (PE) and polycaprolactone (PCL) nano‐fibers are fabricated using a porous membrane as template. The surface characteristics and physical properties of the samples yield different geometries, which determine the wetting and adhesive properties of the fabricated samples. Oriented and wave‐like shapes fibers present the Gecko effect, thanks to their ability to comply and hydrophobic asperities that uphold the water droplet when the wetting properties were tested. The samples are also found to be self‐cleaning due to their high contact angles and low contact angle hysteresis. Adhesion tests results prove that the samples are high reversible adhesion with the ability to stick to smooth surface in a dry and underwater environment. The adhesion on the samples can be enhanced with a double fibril layer or buckling property. They adhere better when the surface is not hydrophilic. By behaving in similar way as the real geckos, the results of this study show that the fabricated samples effectively present the Gecko effect. POLYM. ENG. SCI., 57:283–290, 2017. © 2016 Society of Plastics Engineers     

Effects of ultraviolet irradiation treatment on the surface properties and adhesion of moso bamboo (Phyllostachys pubescens)

The poor adhesion of bamboo coatings is a serious issue in the bamboo industry. To overcome this problem it is necessary to modify the actual surface of the bamboo before finishing. A study on the surface properties and adhesion of moso bamboo (Phyllostachys pubescens) were investigated with various UV irradiation conditions including irradiation time and dose using different UV lamps. Two types of wood coatings, i.e., solvent‐borne nitrocellulose (NC) lacquer and waterborne polyurethane (PU) coating, were used in the study, and 180° peel strength and shear strength tests for measuring adhesion of films were conducted. The results revealed that the wettability and the carbonyl group concentration of the bamboo surface were increased. This was particularly apparent for an irradiation time less than 15 s with a mercury UV lamp (H‐lamp), rated at an intensity of 100 W/cm kept at a distance of 15 cm. In all the treatments, the greenish appearance of moso bamboo was retained and the adhesion was improved. Especially, using solvent‐borne NC lacquer finishing, the higher‐dose (under a mercury UV lamp combined with metal halide lamp; H + M‐lamps) irradiated bamboo had the best adhesion, while, for waterborne PU coating, the H‐lamp irradiated one showed the best improvement. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhanced adhesion force based on microphase separation induced by complexation of ferric ions and polyurethane matrix

Waterborne polyurethane elastomer (WPU) has been widely used as a glue, but it still has some drawbacks, including a long cure time and weak adhesive force. In order to overcome these drawbacks, a new composite [PU/ferric ion complexation (Fe/PU)] with high adhesive strength was successfully prepared using ferric ion (Fe³⁺) as a complexing agent. Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, and tensile testing were used to characterize the chemical structure and mechanical properties of the as‐obtained composites. Introduction of the ferric ion induces a certain degree of microphase separation, resulting in better mechanical strength and interfacial adhesion. The mechanical properties of the PU composite with ferric ions are higher than that of pure PU. The adhesive strength of the 25%‐Fe/PU composite is 32.46 ± 3.1 MPa, exhibiting superior adhesive strength. The tensile strength was enhanced 34%, and the elongation was enhanced 23.6% compared to pure PU. Furthermore, the Fe/PU composite, coordinated with ferric ions, exhibits an enhanced storage modulus and reduced loss coefficient compared to PU. We can foresee that Fe/PU composites will play an important role in the building and engineering areas. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46069.     

UP/PU嵌段共聚树脂/玻璃纤维界面粘结性的研究

合成了一种异氰酸酯嵌段共聚改性不饱和聚酯树脂(UP/PU),并以玻纤增强制备了复合材料(GFRP)。通过接触角、拉伸性能、弯曲性能测定和扫描电镜观察研究了UP/PU GFRP界面的粘结性能。结果表明:UP/PU树脂与玻璃表面的接触角为20°,对玻璃表面的润湿性较通用邻苯型UP好;GFRP拉伸强度1 050 MPa,弯曲强度1 220 MPa,较通用邻苯型UP的GFRP分别提高了145%和78%,说明UP/PU与玻纤的界面粘结性能较好。     

Grafting of Epoxy Resin on Surface-modified Poly(tetrafluoroethylene) Films

An epoxy/PTFE composite was prepared by curing the epoxy resin on the surface-modified PTFE film. Surface modification of PTFE films was carried out via argon plasma pretreatment, followed by UV-induced graft copolymerization with glycidyl methacrylate (GMA). The film composite achieved a 90°-peel adhesion strength above 15 N/cm. The strong adhesion of the epoxy resin to PTFE arose from the fact that the epoxide groups of the grafted GMA chains were cured into the epoxy resin matrix to give rise to a highly crosslinked interphase, as well as the fact that the GMA chains were covalently tethered on the PTFE film surface. Delamination of the composite resulted in cohesive failure inside the PTFE film and gave rise to an epoxy resin surface with a covalently-adhered fluoropolymer layer. The surface composition and microstructures of the GMA graft-copolymerized PTFE (GMA-g-PTFE) films and those of the delaminated epoxy resin and PTFE film surfaces were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle and scanning electron microscope (SEM) measurements. The delaminated epoxy resin surfaces were highly hydrophobic, having water contact angles of about 140°C. The value is higher than that of the pristine PTFE film surface of about 110°. The epoxy resin samples obtained from delamination of the epoxy/GMA-g-PTFE composites showed a lower rate of moisture sorption. All the fluorinated epoxy resin surfaces exhibited rather good stability when subjected to the Level 1 hydrothermal reliability tests.     

Wettability of porous anodic aluminium oxide membranes with three-dimensional,layered nanostructures

The architecture-dependent wettability of three-dimensional (3D), porous anodic aluminium oxide (AAO) membranes with varying surface morphologies including hierarchical, mesh and honeycomb nanostructures is reported. The surface morphology and underlayer structure play different roles in regulating the wetting behaviour of the AAO membranes. For the mild AAO membranes, the wetting behaviour of the ultra-thin top layer is dominated by the surface morphology in which the water contact angles (WCAs) of the AAO membranes with hierarchical, mesh and honeycomb structures are approximately 113.7°?±?4.6°, 94.9°?±?0.7° and 98.8°?±?5.8°, respectively. The wetting behaviour of the 3D, layered AAO membranes is dominated by both the surface morphology and the underlayer structure. Notably, the WCA of the mild AAO membrane with a layered hierarchical structure increases in the second layer (increase in the hole density). The WCAs of the three kinds of layered hard AAO membranes decrease in the second layer (increase in the hole depth) and then decrease slowly or increase in the third transition layer (decrease in the hole density). The WCAs of all the AAO membranes decrease linearly at different rates with the formation of the ordered bottom layer. The above results can facilitate the engineering of nanostructures for controlling the surface wetting behaviour of materials and devices for applications in multiple fields.