Plasma Treatment of Wood–Plastic Composites to Enhance Their Adhesion Properties

In this study, the adhesion properties of adhesives and paints on wood–plastic composites (WPCs) after plasma treatment at atmospheric pressure and ambient air were investigated. Surface energy determination by means of contact angle measurements according to the Owens–Wendt approach and atomic force microscopy to detect changes in surface topography were carried out. An increase in the polar component of surface energy and an increase in surface roughness after plasma treatment were detected, indicating enhanced bond strength. To confirm these results, bond strength tests were conducted. By tensile bond strength tests, increased adhesion of waterborne, solventborne and oil-based paints on plasma treated surfaces was found. Furthermore, by shear bond strength tests, an increase in bond strength of plasma treated WPCs bonded with poly(vinyl acetate) and polyurethane adhesives was ascertained.     

A New Concept for Adhesion Promotion in Metal–Polymer Systems by Introduction of Covalently Bonded Spacers at the Interface

A new concept for molecular interface design in metal–polymer systems is presented. The main features of this concept are the replacement of weak physical interactions by strong covalent bonds, the flexibilization of the interface for compensating different thermal expansions of materials by using long-chain flexible and covalently bonded spacers between the metal and the polymer as well as its design as a moisture-repellent structure for hindering diffusion of water molecules into the interface and hydrolysis of chemical bonds. For this purpose, the main task was to develop plasmachemical and chemical techniques for equipping polymer surfaces with monotype functional groups of adjustable concentration. The establishing of monotype functional groups allows grafting the functional groups by spacer molecules by applying usual wet-chemical reactions. Four processes were favoured for production of monotype functional groups by highly selective reactions: the plasma bromination, the plasma deposition of plasma polymers, the post-plasma chemical reduction of O-functionalities to OH-groups, and the chemical replacement of bromine groups by NH₂-groups. The grafting of flexible organic molecules as spacers between the metal layer and polymer improved the peel strength of the metal. To obtain maximal peel strength of aluminium coatings to polypropylene films and occurrence of cohesive failure in the polypropylene substrate, about 27 OH groups per 100 C-atoms or 6 COOH groups per 100 C-atoms were needed. Introducing C_6–11-aliphatic spacers 1 OH or COOH group per 100 C-atoms contributed about 60% of the maximal peel strength of the Al–PP system, i.e. 2 or 3 spacer molecules per 100 C-atoms were sufficient for maximal peel strength.     

Metal–thermoplastic urethane hybrids in environmental exposure

The long-term properties of injection moulded metal–thermoplastic urethane (TPU) hybrids were studied. The hybrids manufactured with different metal substrates, namely copper, stainless steel and aluminium, were compared, using two surface modifications for copper and stainless steel. N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane was used as coupling agent. It is concluded that the bond mechanism of the silane on different substrate differs, affecting the long-term behaviour of the respective hybrids. The thick layers of silane coupling agent on copper and stainless steel are sensitive to hydrolysis; thus the resistance in humid conditions is quite low. The high temperature exposure increased the bond strength and the fraction of cohesive failure in TPU in copper–TPU, aluminium–TPU and polished steel–TPU hybrids. The last one has native mixed oxide, contrary to controlled oxidised stainless steel, where adhesion decreased after any long-term experiments. This is suggested to derive from hydrogen bonding of the coupling agent to the surface Fe₂O₃ oxide.     

Surface Energy and Adhesion in Composite–Composite Adhesive Bonds

In the absence of weak boundary layers, surface energy can be an excellent indicator of the suitability of a fiber-reinforced composite surface for adhesive bonding. Mechanical surface treatments such as grit blasting are effective and commonly used to prepare composite surfaces, but the roughness introduced by these treatments makes quantification of the surface energy by contact angle methods difficult. This paper shows that the diameter of a small drop of a low-viscosity fluid chosen to have surface tension characteristics very similar to the adhesive can be used as an effective predictor of adhesive bond fracture energy. This technique could form the basis of a sensitive quality assurance tool for manufacturing.     

Platinum–Vanadium Oxide Nanotube Hybrids

The present contribution reports on the features of platinum-based systems supported on vanadium oxide nanotubes. The synthesis of nanotubes was carried out using a commercial vanadium pentoxide via hydrothermal route. The nanostructured hybrid materials were prepared by wet impregnation using two different platinum precursors. The formation of platinum nanoparticles was evaluated by applying distinct reduction procedures. All nanostructured samples were essentially analysed by X-ray diffraction and transmission electron microscopy. After reduction, transmission electron microscopy also made it possible to estimate particle size distribution and mean diameter calculations. It could be seen that all reduction procedures did not affect the nanostructure of the supports and that the formation of metallic nanoparticles is quite efficient with an indistinct distribution along the nanotubes. Nevertheless, the reduction procedure determined the diameter, dispersion and shape of the metallic particles. It could be concluded that the use of H₂PtCl₆ is more suitable and that the use of hydrogen as reducing agent leads to a nanomaterial with unagglomerated round-shaped metallic particles with mean size of 6–7 nm.     

Metal–insulator transition in boron-ion implanted type IIa diamond

Electrical conductivity measurements for selected boron-ion dopant concentrations have been made on type IIa diamond specimens in the temperature range 1.5–30 K. Samples have been implanted using the CIRA (cold implantation–rapid annealing) process, in which small implantation increments were used followed by high-temperature annealing to achieve a significant reduction in the levels of implantation-induced radiation damage and to obtain maximum boron activation. Further post anneals at temperatures up to 1700°C were carried out. Using this procedure, we have recorded, for the first time, metallic conductivity behaviour in implanted surface layers in single-crystal diamond specimens with boron concentrations measured by secondary-ion mass spectrometry to be of the order of n=10²¹ cm⁻³. The occurrence of a metal–insulator transition in this system is discussed.     

The Adhesion Society Award for Excellence in Adhesion Science—1993

The Adhesion Society Award for Excellence in Adhesion Science for 1993, Sponsored by 3M, will be awarded to Dr. Louis H. Sharpe at the annual meeting of the Society at Williamsburg, Virginia, February 21-26, 1993. Dr. Sharpe was associated with AT&T Bell Labs and worked in the area of adhesion science for over 30 years. Dr. Sharpe is cited in the award:     

Synthesis of ROMP Monomers Containing Metal–Metal Bonds

Methods for the synthesis of cyclic monomers that have both metal–metal bonds and carbon–carbon double bonds are reported. Ring opening metathesis polymerization (ROMP) of these monomers would yield polymers that are photochemically degradable. The first method investigated involved substitution of Cp₂Fe₂(CO)₄ by the bidentate phosphine ligand DPPEN (Ph₂P CH=CH–PPh₂). Cp₂Fe₂(CO)₂( -DPPEN) was synthesized and the X-ray crystal structure is reported but the molecule could not be polymerized by a ROMP method using Grubbs’s catalyst. The inability of this monomer to polymerize (or copolymerize with cyclooctatetraene) was attributed to the bulky phenyl rings being in close proximity to the C=C in the DPPEN ligand, which prevents coordination of the monomer to the catalyst. To decrease the steric interactions, the DPPBN ligand was synthesized (DPPBN=Ph CH CH=CH CH PPh₂). However, the reaction of DPPBN with Cp₂Fe₂(CO)₄ yielded the product Cp₂Fe₂(CO)₂( -1,2,4-triphos), where the 1,2,4-triphos ligand is a tridentate ligand formed by the formal additional of Ph₂PH to DPPBN (1,2,4-triphos=Ph CH CH(PPh₂) CH CH PPh₂). An X-ray structure of the Cp₂Fe₂(CO)₂( -1,2,4-triphos) complex revealed that the 1,2,4-triphos ligand chelates exclusively through the two phosphorus atoms that are bridged by two carbon atoms. It is suggested that this structural feature may simply reflect the increased stability of the 6-membered ring over the 7- and 8-membered rings. The reactions of the Cp₂Mo₂(CO)₆ and Cp₂Mo₂(CO)₄ dimers with DPPBN were investigated next. Reactions of Cp₂Mo₂(CO)₆ and Cp₂Mo₂(CO)₄ with the DPPEN and DPPBN ligands resulted in the disproportionation of the dimers. The X-ray crystal structure of [CpMo(CO)₂(DPPEN)][CpMo(CO)₃] was determined and is reported. The CpMo(CO)(DPPEN)Cl complex was formed when these same reactions were carried out in the presence of CH₂Cl₂. The X-ray crystal structure of this molecule is also reported.     

The Adhesion Society of Japan–Abstracts

Titanium 6-aluminum 4-vandium alloys were etched for varying periods of time in aqueous solution of hydrofluoric acid and ammonium dihydrogen phosphate. Following etching, one-half of the specimens were covered with vacuum evaporated gold while the other half were bonded with a commercial adhesive. Gold adhesion to the alloys was evaluated by pressure sensitive tape peel tests and lap shear tests using a commercial adhesive. The uncoated specimens were evaluated by lap shear tests. Adhesion of Ti6A14V to gold and to the commercial adhesive was directly proportional to the length of time the specimen was etched. Although etching in HF/NH₄H₂PO₄ resulted in a rather rough surface, there were only subtle differences with increasing time. Surface chemistry changes suggest selective etching of the alpha phase and increasing exposure of the beta phase. Heating of the gold on Ti6A14V resulted in improved adhesion, probably by diffusion mechanisms. Exposure to steam resulted in bond degradation in both gold/Ti6A14V and in adhesive/Ti6A14V systems. The adhesive bonding results for the etched specimens were compared to performance based on “attachment site” theory. Excellent agreement for both gold on Ti6A14V and commercial adhesive on Ti6A14V was observed. Degradation of the bond due to steam followed the same form in both systems, suggesting H₂O transport along the interphase.     

Plastic Pallet Project Started in Maoming

On March 1,2005.Plastic Pallet Produc-tion(Maoming)Co.,Ltd.(PPP Maoming)was formally set up by Switzerland com-pany-PPAL AG,the largest producer oftechnical plastic pallet in the globe.PPALwill construct solely the technical plasticpallet production site in Maoming Petro-chemical Industrial Zone,Guangdongprovince with a capacity of 60 millionpieces/a,which is the largest scale in the     

Opportunities and Challenges in Biomedical Applications of Metal–Organic Frameworks

Journal of Inorganic and Organometallic Polymers and Materials - Unique chemical and physical properties of metal–organic framework (MOF) nanoparticles suggest them as promising candidates...     

Effectiveness of Metal–Metal and Metal–Organic Compound Combinations Against Plutella xylostella: Implications for Plant Elemental Defense

Plants that contain elevated foliar metal concentrations can be categorized as accumulators or, if the accumulation is extreme, hyperaccumulators. The defense hypothesis suggests that these plants may be defended against folivore attack, and recent research has indicated that metal concentrations at or below the accumulator range may be defensively effective. This experiment explored the toxicity of four metals hyperaccumulated by plants (Cd, Ni, Pb, and Zn) and asked if combinations of metals, or metals and organic chemicals, might broaden the defensive effectiveness of metals. Metals were used alone and in certain metal + metal (Zn plus Ni, Pb, or Cd) and metal + organic defensive chemical (Ni plus tannic acid, atropine, or nicotine) combinations. Artificial diet amended with these treatments was fed to larvae of the crucifer specialist herbivore Plutella xylostella. Combinations of metals and metals + organic chemicals significantly decreased survival and pupation rates, compared to single treatments, for at least some concentrations in every experiment. Effects of combinations were additive rather than synergistic or antagonistic. Because Zn enhanced the toxicity of other metals and Ni enhanced the toxicity of organic defensive chemicals, our findings suggest that the defensive effects of metals are more widespread among plants than previously believed. They also support the hypothesis that herbivore defense may have led to the evolution of metal hyperaccumulation by increasing the preexisting defensive effects of metals at accumulator levels in plants.     

Synthesis and Study of Multifunctional Cyclodextrin–Deferasirox Hybrids

Metal dyshomeostasis is central to a number of disorders that result from, inter alia, oxidative stress, protein misfolding, and cholesterol dyshomeostasis. In this respect, metal deficiencies are usually readily corrected by treatment with supplements, whereas metal overload can be overcome by the use of metal-selective chelation therapy. Deferasirox, 4-[(3Z,5E)-3,5-bis(6-oxo-1-cyclohexa-2,4-dienylidene)-1,2,4-triazolidin-1-yl]benzoic acid, Exjade, or ICL670, is used clinically to treat hemosiderosis (iron overload), which often results from multiple blood transfusions. Cyclodextrins are cyclic glucose units that are extensively used in the pharmaceutical industry as formulating agents as well as for encapsulating hydrophobic molecules such as in the treatment of Niemann–Pick type C or for hypervitaminosis. We conjugated deferasirox, via an amide coupling reaction, to both 6^A-amino-6^A-deoxy-β-cyclodextrin and 3^A-amino-3^A-deoxy-2^A(S),3^A(S)-β-cyclodextrin, at the upper and lower rim, respectively, creating hybrid molecules with dual properties, capable of both metal chelation and cholesterol encapsulation. Our findings emphasize the importance of the conjugation of β-cyclodextrin with deferasirox to significantly improve the biological properties and to decrease the cytotoxicity of this drug.     

Evaluation of Adhesion Forces in Alginate–Filler System Using an AFM Colloidal Probe Technique

Interaction and adhesion forces between polymer and mineral fillers are key factors in controlling their affinity during the preparation of high-quality nanobiocomposites. In this work, the compatibility between polymer (alginate) and mineral filler (mica, borax or bentonite) surfaces was characterized by direct force measurements using atomic force microscopy (AFM). Direct force measurements, using a single spherical alginate particle prepared by the spinning disc atomization method and attached to a cantilever, have been employed to characterize adhesion forces between alginate and several mineral filler surfaces in air. The free energies of adhesion for alginate–mica, alginate–bentonite and alginate–borax systems were compared. The experimental adhesion forces for these systems were compared with those predicted using the Johnson– Kendall–Roberts (JKR) approximation and the Liftshitz–van der Waals and Lewis acid–base interaction theory. The discrepancies between the experimental values and theoretical predictions were discussed on the basis of the surface roughness effect on the measured adhesion forces.     

Evaluation of the Effect of Nanosilica on Thermal and Mechanical Properties of Metal–Metal and Metal–Glass Canola-Based Polyurethane/Nanosilica Adhesives

Nanocomposites with different concentration of nanofiller were prepared by adding nanosilica to the canola-based polyurethane matrix via in situ polymerization. The effect of nanosilica on the mechanical properties of adhesives was evaluated by tensile tests. Adhesive characteristics on metal–metal and metal–glass bondings were also evaluated by lap shear strength tests. Incorporation of nanosilica into the canola-based polyurethane enhanced both tensile and lap shear strength of synthesized adhesives. Also the effect of nanoparticles on glass transition temperature and thermal stability was investigated by differential scanning calorimetry and thermogravimetric analysis, respectively. The increase of nanosilica content in the polyurethane adhesives, thermal property of the nanocomposites improved.     

Spherical Nanoparticle–Substrate Adhesion Interaction Simulations Utilizing Molecular Dynamics

From a molecular perspective, the fundamental rolling and sliding elasto-adhesion interactions between a spherical nano-particle and an elastic substrate is studied using a computational technique based on the Molecular Dynamics (MD) approach. Initially, the particle and the substrate were equilibrated individually at 300 K. The covalent bonds interactions between the atoms of the nanoparticle are modeled by constraining the atoms to stay together throughout the simulation. The temperature of the substrate atoms is regulated by periodically scaling to mimic the bulk substrate effect to minimize the effects of the finite substrate size. The intermolecular interaction between the particle and the substrate is defined by the Lennard–Jones (LJ) 12-6 potential. The total force–displacement curves of the 4.2 and 7.89 nm particles in the cases of particle being pushed normally towards the substrate and the particle pushed tangentially, while in adhesion with substrate, are obtained. The rolling resistance moment exhibited by the smaller nanoparticle (4.2 nm) is calculated from the force–displacement curve obtained from simulations and compared to the theoretical predictions based on a two-dimensional adhesion model. It is found that the moments as a function of the rotation angle are of the same order (3.64 nN nm). The rolling and sliding force–displacement profiles when the nanoparticle is subjected to tangential load are also presented.