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Improved Adhesion Properties of Polyurethane Adhesive Containing Fumaric Acid
Abstract
Different amounts (0.5–3 wt%) of fumaric acid (FA) were added to a solvent-based polyurethane (PU) adhesive. Addition of FA produced a decrease in viscosity and changed the rheological and viscoelastic properties of the liquid PU adhesive, which was more marked upon increasing the time after the adhesive was prepared and more noticeable for high amounts of FA. According to molecular weight distribution, differential scanning calorimetry, thermal mechanical analysis and thermogravimetry measurements, the addition of FA seemed to produce a reaction with the polyurethane (possibly an acid-catalyzed transesterification reaction) which resulted in chain cleavage, disruption of polyurethane crystallinity and a loss of physical properties. These modification in PU structure did not affect the surface energy value of the PU adhesive although the T-peel strength of roughened rubber/PU adhesive/roughened rubber joints increased when the PU adhesive contained FA. This improvement was due to the removal of antiadherent substances (zinc stearate, paraffin wax) from the rubber surface produced by migration of FA to the PU adhesive surface once the adhesive joint was formed. Therefore, the carboxylic acid seemed to act as a compatibilizer between the rubber surface and the PU/adhesive interface.
This chapter discusses the mechanisms and factors involved in the adhesion between vulcanized rubber and vulcanized rubber. The bonding between two vulcanized rubber layers is achieved with the help of special bonding agents that stitch both vulcanized rubber surfaces and improve the bond strength. The mechanism of adhesion between two vulcanized rubber layers is different from that of unvulcanized or partially vulcanized rubbers. The sulfur‐vulcanized styrene‐butadiene rubber (SBR) rubber was surface modified by solvent wiping using organic solvents and chlorination using trichloroisocyanuric acid (TCI). A vulcanized SBR, about 5 mm thick, was prepared using a moulding process after open‐mill mixing. In order to determine the adhesion properties of vulcanized SBR rubber, roughened or unroughened plus chlorinated SBR rubber/polyurethane adhesive joints were prepared. The percentage of oxygen on the SBR rubber surface increased with the concentration of TCI. Also, the percentage of oxygen on the SBR rubber surface increased with the extended plasma treatment.
With the increasing costs in the disposal of wastes from various industrial activities, strategies to find solutions to waste utilization have gained attention. In the present study, sweet lime pomace-based containers were developed with the varying proportion of polyvinyl alcohol (6, 9 & 12%), and starch (6, 9 & 12%) by keeping the ratio of sodium carboxy methyl cellulose constant (2%). The sweet lime pomace powder was added to the mixture to make it to 100%. The selected containers exhibit the most desirable properties in terms of water absorption, soluble matter presence, textural, and biodegradability. To further enrich their properties, a layer of modified bee wax was applied on to the containers which could hold the hot liquid up to 70 °C for 10 min. The modified bee wax was prepared by adding ZnSt2 (0, 5, 10 &15%) in bee wax that conferred higher temperature tolerance and better barrier properties.
This study aims to provide further understanding on the depolymerization of polyurethanes (PU) via acidolysis. Therefore, polyurethane foams scraps are chemical recycled using different dicarboxylic acids, namely succinic and phthalic dicarboxylic acids, being the reaction products identified using Fourier‐transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography. The results obtained show that succinic acid has higher efficiency as cleavage agent, as a result, the succinic acid ensuing recovered polyol (RP) presents higher hydroxyl value and lower viscosity. Additionally, from the oxidative‐induction time measurements, it is observed that the RP is considerably more thermally stable, than the petroleum‐based polyol, due to the higher content of aromatic moieties. Afterwards, the RP is used as substitute of petroleum‐based polyol in the production of polyurethane adhesives (PUA) and compared with conventional polyol based PUA. Due to the higher content of aromatic moieties, higher bonding strength is achieved using the RP. Overall, further understanding on the acidolysis is obtained, proving the suitability of this method for the recycling of PU.
This chapter contains sections titled: Introduction Co‐crosslinking Adhesion Between Vulcanized Rubber and Unvulcanized Rubber or Partially Vulcanized Rubber Adhesion Between Vulcanized Rubber and Vulcanized Rubber Summary Acknowledgements List of Symbols List of Abbreviations
A new series of acrylic adhesive mixtures was specifically designed for use in strabismus surgery, more precisely to join the rectus muscles to the sclera. These two-part adhesives consisted of a mixture of ethyl cyanoacrylate (CN) and ethyl carboxyacrylate (ECA). ECA acted as a plasticizer imparting flexibility to the CN, and also as a nonreactive diluent, serving to reduce the exotherm in the reaction between CN and eye tissues. In this article, the synthesis of the ethyl carboxyacrylate is described, and the properties of different ethyl cyanoacrylate + ethyl carboxyacrylate mixtures were studied. The curing reaction of the adhesive mixtures was monitored using Fourier transform infrared (FTIR) spectroscopy and scanning differential calorimetry (DSC). The rheological properties of the cured CN-ECA adhesive films were studied using plate-plate rheometer experiments. To quantify the adhesion, single lap-shear tests produced between a rubber and the adhesive mixtures were performed and, to evaluate the adhesion to eye tissues, tensile strength measurements of superior rectus muscle/adhesive mixture/sclera joints were carried out. The 70CN-30ECA (v/v) adhesive mixture provided the most adequate balance between adhesion and mechanical properties in the joining of the superior rectus muscle to the sclera. The glass transition temperature of the CN-ECA adhesive mixtures linearly decreased with increase in the ECA content, and a lower degree of conversion during polymerization was obtained by increasing the ECA content. As a consequence, the CN-ECA mixtures were less stiff than CN, giving better performance in the joining of the rectus muscles to the sclera. Finally, the adhesion of CN was sufficiently decreased in CN-ECA mixtures, and the locus of failure was directed to the adhesive film in the joint between the rectus muscles and the sclera.
We have prepared composites of polyvinyl acetate (PVAc) reinforced with solution exfoliated graphene. We observe a 50% increase in stiffness and a 100% increase in tensile strength on addition of 0.1vol% graphene compared to the pristine polymer. As PVAc is commonly used commercially as a glue, we have tested such composites as adhesives. The adhesive strength and toughness of the composites were up to 4 and 7 times higher, respectively, than the pristine polymer.
Die Hydrolysebeständigkeit von Polyurethanelastomeren, die aus höhermolekularen Hydroxy‐ bzw. Aminoverbindungen, Diisocyanaten und Kettenverlängerern aufgebaut sind, wird in Abhängigkeit von der Konstitution der höhermolekularen Hydroxyverbindungen und den angewandten Mengenverhältnissen der drei Baukomponenten untersucht. Ausgehend von den höhermolekularen Hydroxyverbindungen auf Polyätherbasis bis zu den Polyestern wird gezeigt, daß die Hydrolysebeständigkeit der Polyurethanelastomeren sowohl durch zunehmend hydrophobe Eigenschaften der höhermolekularen Hydroxyverbindungen als auch durch die Erhöhung der Diisocyanat‐Kettenverlängerer‐Mengen verbessert wird. Polyurethanelastomere mit der höchsten Hydrolysebeständigkeit werden aus 1,6‐Hexandiolpolycarbonat erhalten.
This paper describes the monomer types commonly used in making thermoplastic polyurethane elastomers. It gives chemical structure of the polymers and their general properties. Also de scribed are studies of the hydrolysis of thermoplastic polyurethane elastomers. This will include information on author's choice of hydrolysis stability test, the influence of polymer structure on hydrolysis stability, and the discovery of the dominant factor in poly(ester-urethane) hydrolysis stability. Effective ways of im proving the hydrolysis stability of poly(ester-urethanes), and the adverse effect of added carboxylic compounds are also de scribed. The hydrolysis stability of thermoplastic poly(ester-ure thane) elastomers based on the special-structured polyester-glycol, poly(ε-caprolactone), is also discussed. Hydrolysis stability characteristics of two types of thermoplastic poly(ether-urethanes) are discussed.
The aim of this paper is to contribute to the understanding of the nature of the changes produced in SBR samples by modifying their surface characteristics and using different techniques: peel strength tests, scanning electron microscopy (SEM), contact-angle measurements, and infrared spectroscopy (FTIR). The combination of all of these experimental procedures would give a more detailed idea about the SBR surface modifications. On the other hand, a comparison with previously published papers relating to the same subject will also be considered.
Surface modifications produced by treatments (mainly halogenation) of synthetic vulcanized styrene-butadiene rubber (SBR) leading to increased adhesion properties with polyurethane adhesives have been studied. T-peel tests, scanning electron microscopy (SEM), advancing contact angle measurements, infra-red (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC) were used to analyze the nature of surface modifications produced in the rubber. Although some surface heterogeneities were created, physical treatments (ultrasonic cleaning, solvent wiping, abrasion) did not noticeably increase the adhesion strength because certain abhesive substances (e.g. zinc stearate, paraffin wax) cannot be removed from the rubber surface by such treatments. Chemical treatment (chlorination) was carried out using ethyl acetate solutions of trichloroisocyanuric acid (TCI) (1,3,5-trichloro-1,3,5-triazine-2,4,6-trione). Chlorination of SBR with trichloroisocyanuric acid produced a significant improvement in T-peel strength, due to the contribution of mechanical (surface roughness, microcracks), thermodynamical (increase of polar contribution to the surface energy) and chemical (removal of abhesive substances, creation of polar groups) rubber surface modifications. The strong adhesion between the chlorinated SBR surface and the polyurethane adhesive was due to the presence of oxidized species of >C=O, -C-OH and -COR type. Chlorination of SBR is a fast reaction which needs only a small concentration of chlorination agent (< 1 wt% TCI/ethyl acetate) to produce high adhesion levels. An increased amount of TCI facilitated the chlorination reaction progressing from the exterior to the internal rubber bulk; however, although a thicker layer of chlorinated rubber created no further increase in adhesion strength was obtained.
Halogenation of styrene-butadiene rubbers has been carried out using solutions containing different amounts (0.1-5 wt%) of trichloroisocyanuric acid in butan-2-one. The treated rubber surface showed increased peel strength in joints made with polyurethane adhesive. The effects of chlorination on the rubber surface were studied using scanning electron microscopy, contact angle measurements, and infrared spectroscopy. It was shown that cracks appear in the rubber surface after halogenation, a factor which favours adhesion; the larger the amount of trichloroisocyanuric acid used, the larger the number of cracks. On the other hand, chlorination of the carbon double bond (butadiene) and the formation of carboxylic acid groups seem to be the most important chemical changes in the chlorinated rubber surfaces. Chlorination increases the surface energy of the rubber, although this increase is a function of the rubber composition. In fact, for a simple rubber formulation, the polar component of the surface energy increases for the highest concentrations of chlorine on the rubber surface; but for rubber with a more complicated formulation, the same value of surface energy after chlorination was obtained, independently of the amount of trichloroisocyanuric acid added. A good correlation was found between the contact angle measurements, the infrared spectra, and the peel strength values.
The influence of the addition of silica (Aerosil-200) (5-25 wt%) to polyurethane adhesives on their adhesion properties with non-chlorinated and surface-chlorinated rubbers has been studied. The chlorinating agent was Trichloroisocyanuric acid (TIC) in 2-butanone solution at a concentration of between 1 and 9 wt%. In general, silica produced an increase in the adhesive viscosity and an improvement of green (immediate) peel strength (especially with chlorinated rubber). The best results were obtained for a silica content of 10-20 wt%. However, the addition of silica did not improve the peel strength after a thermal ageing process. Polyurethane adhesives containing silica undergo an improvement in their resistance to degradation by chlorine on the rubber surface. On the other hand, the chlorination of silica produces the rupture of Si-O bonds and the formation of Si-H and Si-Cl groups. Furthermore, the stirring speed (directly related to the dispersion) of silica into the adhesive is an important parameter which affects the viscosity and peel strength. A stirring speed of 1000 rpm gives the best silica dispersion.
In this paper two kinds of weak boundary layers (WBL) in synthetic vulcanized styrene-butadiene rubber are described.
i) WBL produced by the presence of antiadhesion compounds of the rubber formulation (zinc stearate, microcrystalline paraffin wax). These WBL cannot be effectively removed by solvent wiping, whether followed by washing with an ethanol/water mix or not. Although this treatment allowed a significant removal of zinc stearate, the paraffin wax concentration on the surface was not greatly reduced, thus, poor adhesion of rubber was obtained. Chlorination with small amounts of ethyl acetate (EA) solutions of trichloro isocyanuric acid (0.5–5 wt% TCI/EA) and/or an extended halogenation treatment increased the adhesion strength and effectively eliminated the zinc stearate from the rubber surface. If an additional heat treatment (50°C/24h) of the chlorinated rubber was also carried out, the WBL was more effectively eliminated and the resulting adhesion was independent of the amount of chlorination agent applied to the rubber surface. Furthermore, this heat treatment favoured the elimination of WBL in the untreated rubber and also contributed to the removal of WBL produced by an excess of halogenation agent.
ii) WBL created by an excess of chlorination agent applied to the rubber surface. The excess of chlorination agent produced lack of adhesion in the rubber because there was significant damage of the rubber surface and a non-rubber surface layer was formed (mainly due to oxidized, chlorinating agent residues and cyanuric acid), which contributed to the formation of WBL. To avoid the creation of WBL, a postchlorination treatment of rubber with a solution of 25 wt% ethanol in water followed by a vacuum-drying process produced excellent results. The effectiveness of this treatment relied on combining an adequate degree of chlorination with no external surface deterioration of the rubber by the excess of chlorination agent.
Improvement of the adhesion capacity of polypropylene to aluminium can be obtained by adding a small quantity of maleic anhydride grafted polypropylene to the polymer. With increasing maleic anhydride content, the peel strength of the polymer-aluminium assembly first increases due to migration, orientation and chemical bonding, and then decreases as a result of the formation of a weak boundary layer, made of the low molecular weight grafted polymer chains. This study stresses the importance of two phenomena in adhesion: the restructuring of the polymer at the metal interface and the formation of an interphase.
Grafting small quantities of acrylic acid onto polyethylene has been shown to improve considerably the adhesion properties of the polyethylene, especially to aluminum. The enhanced adhesion with grafted polyethylene appears to be related to the orientation of acrylic groups in the polymer/metal oxide interface and to the formation of chemical linkages between the metal oxide and the oriented carboxylic groups. A new method of improving the water resistance of the grafted polyethylene/aluminium interface is also examined.