Biodeterioration of adhesives based on thermoplastic polyurethanes under the action of soil microorganisms

Results of an investigation of the resistance of thermoplastic polyurethanes to the action of biological factors are presented. The mechanism of polyurethane destruction is described. The limiting stage of biostability is shown to be the surface biodeterioration of the material.     

Synthesis and properties evaluation of quaternized polyurethanes as antibacterial adhesives

We present new side‐chain quaternized polyurethanes as antibacterial adhesives made by polyaddition polymerization followed by quaternization for different time intervals. The degree of quaternization of N‐diol units in the polymer is changed from 13.6 to 99.0 mol % (almost complete) for tuning the antibacterial action (leaching/contact type) and studying effect on adhesive strength. The degree of quaternization of about 26 mol % provided the nonleaching antibacterial effect with adhesive strength more than 60 N cm^?2 on aluminum and glass substrates. The increase in the degree of quaternization enhanced polymer polarity shifting nonleaching (contact type) antibacterial behavior to the leaching type but maintaining the high adhesive strengths. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 752–757     

Photooxidation of dyed styrene-butadiene and natural rubbers

Dyed natural rubber (NR) and styrene-butadiene rubber (SBR) designed for outdoor applications were exposed to accelerated artificial aging in xenon light. The aging results in the deterioration of the properties of the exposed surface material. The ability of dyed polymers to withstand prolonged sunlight exposure without fading or undergoing any physical deterioration is largely determined not only by the photochemical characteristics of the absorbing dyestuff itself but also by the polymer structure and fillers. Results indicate that dyed filled NR and SBR samples behave differently during photooxidation. The photodegradation products were observed by Fourier transform infrared spectroscopy (FTIR) to characterize the changes occurring in the polymer matrix during UV aging. The fading of the dyed polymers was found to be promoted in the NR sample. Moreover, the effects of photooxidation on the dyed SBR and NR materials were assessed by the formation of cracks and the thickness of the degraded area. The degradation thickness is more important for the NR sample than for the SBR one according to environmental scanning electron microscopy (ESEM) observations. For the NR sample, cracks appear initially at the surface and then grow through the thickness of the specimen, while for the SBR sample cracks are small and discontinuous. Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 6, pp. 1081–1085. This article was submitted by the authors in English.     

Ambient curable latex films and adhesives based on natural rubber bearing Acetoacetoxy functionality

The study described in this paper first demonstrates that a newly modified form of natural rubber, namely graft copolymers of natural rubber with poly (acetoacetoxyethyl methacrylate), NR‐g‐PAAEM, is able to undergo a cross‐linking reaction at room temperature by reaction with a water dispersible polyisocyanate based on hexamethylene diisocyanate (poly‐HDI). Attenuated total reflectance Fourier transform infrared (ATR‐FTIR) analysis indicated that amide groups were formed by the reaction of the acetoacetyl groups (AcAc) present in the grafted poly (acetoacetoxyethyl methacrylate) (PAAEM) chains with the poly‐HDI. This observation was accompanied by a noticeable increase in the tensile strength of the NR‐g‐PAAEM latex films when adding poly‐HDI to the latex prior to film formation. DMTA analyses also revealed a shift in the tan δ peaks, corresponding to the transitions of both NR‐g‐PAAEM and free PAAEM phases, to higher temperatures. These results provide firm evidence of cross‐linking between NR‐g‐PAAEM chains by reaction with poly‐HDI during film formation under ambient conditions. Adhesives for bonding wood to wood based on the NR‐g‐PAAEM latex were then prepared, using poly‐HDI as the cross‐linker. The lap shear strength of the resulting adhesives exhibited a maximum value of 2657 KPa when a poly‐HDI:AAEM molar ratio of 3:1 was employed. It was also observed that the adhesive attained about approximately 89% of the highest lap shear strength after it was allowed to set at 30°C for 24 hours. Hence, the use of poly‐HDI in cross‐linking NR particles bearing grafted PAAEM offers great potential for developing latex adhesives and coatings capable of curing under ambient conditions.     

Frost- and heat-resistant composite materials based on polyurethanes

Based on a mixture of 2,4 and 2,6-tolylene diisocyanate of a grade Desmodur T-80 and polyesters P6-BA and PDA-800. Reactive isocyanate-containing prepolymers for polyurethane composite materials were synthesized. On the basis of alkanolamine Lapromol A-294, polyesters of various structures and an aromatic diamine Curalon M curing systems for polyurethane composites were developed. The effect of a ratio of isocyanate-, hydroxyl-, and amine-containing components on the properties of the prepolymers and curing systems was investigated. Polyurethane composites were produced and their performance characteristics were studied.     

Polycaprolactone based biodegradable polyurethanes

Two series of segmented polyurethanes were prepared with systematic variation in soft and hard segment length. The soft segment was constituted by polycaprolactone (PCL) blocks of molecular masses 530 or 2000 and the hard segment (HS) by urethane blocks, in a concentration that varied from 12% to 44% in weight of the whole polyurethane. Morphological analyses indicated that the amount of crystallinity of copolymers was strongly dependent on the PCL molar mass and hard segment content. The copolymers with longer PCL soft segments (Mn=2000) were semicrystalline, but those with shorter PCL segment (Mn=530) were unable to crystallize. The primary factor affectingthe biodegradability of copolymers as evaluated by Sturm tests was the extent of the phase separation, and that the segmental blending of the less biodegradable polyurethane (HS) blocks with PCL in the amorphous phase had a critical unfavorable consequence, which may be attributed to the size of the accessible area by microorganisms.     

Preparation of polymer composites on the base of polyurethanes and natural polysaccharides

A series of composites based on segmented polyurethanes (PU) as polymer matrices and natural polysaccharides – cellulose and starch – as fillers have been synthesized. Using IR method and Differential Scanning Calorimetry the peculiarities of the structure of composites and their behavior in the buffer solutions in conditions imitating natural soil environment have been investigated.     

Structural organoplastics based on film adhesives

The use of VK-36RT film adhesive as a polymer bonding agent for producing structural hermetic organoplastics and VK-3 film adhesive for creating organoplastics with high shock and ballistic resistance for producing protective structures for aerotechnic purposes was considered.     

Synthesis of segmented polyurethanes based on furazan units

Linear polyurethane thermoplastics comprising furazan blocks soluble in organic solvents and having low melting points were obtained by nonequilibrium polycondensation of 3,4-bis(hydroxymethyl)furazan, butane-1,4-diol and 2,4-di-isocyanatotoluene. The thermal behavior of some copolymers was studied by DSC and TGA methods.     

Polychloroprene rubbers used for adhesives: a small angle X-ray scattering preliminary investigation under stretching

Summary Three types of polychloroprene rubbers (Du Pont de Nemours Co. Neoprenes AD, WHV and W) used for adhesives and having different crystallization rates have been investigated.The mechanical properties of the Neoprenes samples were determined and the films were examined under stretching by SAXS for a preliminary investigation on their different superreticular order.

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Zusammenfassung Drei Typen von Polychloropren-Kautschuk mit verschiedener Kristallisationsgeschwindigkeit (Neoprene AD, WHV und W von Du Pont de Nemours), die als Klebemittel dienen, wurden als gedehnte Filme mechanisch und röntgenographisch (SAXS) untersucht. Sie zeigen Unterschiede in der Überstruktur.

     

Thermal degradation of polyurethanes based on xylylene diisocyanates

Polyurethanes derived from xylylene diisocyanates and trans-1,4-cyclohexanedimethanol were thermally degraded by using the techniques of thermogravimetry and pyrolysis at atmospheric pressure. Quantitative determination of the pyrolysis products such as CO₂, diamine, olefin, and starting diol showed that these polyurethanes follow the typical mechanism of degradation via dissociation into starting diol and diisocyanate. Kinetic parameters for the overall degradation reaction were determined using four different methods. The results showed the influence of the experimental technique used when making a comparison of the thermal stability of polymers, as determined by the kinetic parameters of the degradation reactions.     

Investigations on monotropic liquid crystalline polyurethanes based on biphenylol

2,2′-Azobis-[2-cyano-(4-ethylphenol)] (ABCP) was prepared from parahydroxyacetophenone, using hydrazine sulfate and sodium cyanide. Biphenylol ester of ABCP, 2,2′-azobis-[2-p-biphenyloxy-(4-ethylphenol)] (BECP) was synthesized via the acid route. Combined liquid crystalline polyurethanes (CLCPUs) were synthesized from 1,6-diisocyanatohexane (HDI) and BECP in dimethylformamide (DMF) at 110°C under nitrogen atmosphere. The effect of partial replacement of BECP by 4,4′-dihydroxy biphenyl (DHBP) on liquid crystalline (LC) properties was studied. The polymers were characterized by proton and ¹³C NMR, FTIR, and UV spectroscopy. Elemental analysis were done for determining the percentage content of C, H, and N and the molecular weights of the polymers were determined by gel permeation chromatography (GPC). Thermogravimetric investigations (TGA) of the polyurethanes (PUs) were performed to study the decomposition. The LC nature of the PUs was confirmed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Cross-polarized optical microscopy studies demonstrated the existence of two distinct crystalline morphologies, a spherulitic morphology with high mole ratio of DHBP and a thread-like crystalline morphology with that of BECP. All the PUs synthesized showed a LC nature with a wide temperature range. Partial replacement of BECP by DHBP changed the mesomorphic nature, transition temperature, and temperature range of the mesophase. © 1995 John Wiley & Sons, Inc.     

Synthesis and properties of polyester based polyurethanes

Hydroxyl terminated polyesters were prepared by a melt condensation technique using adipic acid and various diols. They were characterised by hydroxyl number, acid number and intrinsic viscosities in benzene. The polyesters were reacted with excess tolylene diisocyanate to yield isocyanate terminated prepolymers and subsequently cured with diols and diamines. These polymers were characterised by i.r. spectra, viscosity measurements and thermogravimetric analysis. The glass transition temperature of the polymers were found to be in the region ?25 to ?55. The influences of prepolymers and curing reagents are discussed with respect to the low temperature flexibility and thermal stability of the polyurethanes.     

Modern synthetic adhesives based on epoxy-rubber compositions

Results of investigations of adhesives and compounds based on epoxy resins modified with low-molecular rubbers are presented. A series of epoxy-rubber compositions with improved physicomechanical characteristics and operational properties are developed. Examples of solutions of engineering challenges using high-molecular synthetic adhesive systems are given.     

Specific heats of guayule and natural rubbers above the glass transition temperature

Heat capacities of guayule and natural rubbers were measured between 228 and 333 K using a DuPont 990 Differential Scanning Calorimeter. Data obtained were fitted to a straight line. We obtained the following equations where C_p is given in cal g^?1 K^?1. For guayule rubber, C_p = 22.6152 × 10^?4T + 0.7731 (correlation factor = 0.99). For natural rubber. C_p = 16.9195 × 10^?4T + 0.9209 (correlation factor = 0.98). Furthermore, some theoretical considerations and instrumental conditions were analyzed so that the determinations of heat capacities could be improved.     

Novel biomimetic adhesives based on algae glue

Inspired by the remarkable adhesive capabilities to wet surfaces of the secretes of the brown alga Fucus serratus, novel glues have been designed and characterized. Formulations composed of phloroglucinol, alginate, and calcium ions are capable of adhering to a variety of surfaces. Rheological data show that the presence of phloroglucinol lowers the amount of Ca(2+) ions required for sol-gel transition, which indicates interactions between the alginate and the phloroglucinol. SAXS data support this claim. The phloroglucinol adhesive binds porcine tissues together with an adhesive strength of 17-25 kPa, which indicates appropriate mechanical properties for application as a soft tissue adhesive.     

Heat-conducting adhesives based on modified epoxy resins

Main characteristics of heat-conducting adhesive materials used to withdraw heat from warming elements of devices and the joints of electrotechnical equipment are presented. The developed materials, i.e., TsMK-TP adhesive pastes and TPK convenient for application adhesives, are cold-curing compositions based on epoxy-diane resins modified with Laproxide products. They have heat conductivity coefficients of no less than 1.8 W/(m K), are workable in the temperature range of −196 to 150°C (up to 200°C for a short period of time), and do not contaminate optical elements due to minimal gas release under exposure to vacuum and increased temperatures.     

Sugar‐based hydrophilic polyurethanes and polyureas

Novel linear homogeneous polyurethanes and polyureas with enhanced hydrophilic character have been successfully prepared from sugar‐based monomers having their hydroxyl groups free or partially protected. By the reaction of primary hydroxyl groups of xylitol with dimethyl hexamethylene dicarbamate (HMDC) or di‐tert‐butyl‐4,4′‐diphenyl methyl dicarbamate (MDC), two new linear semicrystalline polyurethanes [PU(X‐HMDC) and PU(X‐MDC)] have been prepared. Likewise, by the reaction of xylitol with the analogous diisocyanates hexamethylene diisocyanate (HMDI) or 4,4′‐methylenebis(phenyl isocyanate) (MDI), similar polyurethanes [PU(X‐HMDI) and PU(X‐MDI)] were obtained. However, these latter polyurethanes present some degree of crosslinking because of the higher reactivity of the diisocyanate comonomers. Linear hydrophilic polyureas having free hydroxyl groups joined to the main chain have also been prepared by the reaction of the same diisocyanates (HMDI and MDI) with 1,6‐diamino‐1,6‐dideoxy‐D ‐mannitol and 1,6‐diamino‐1,6‐dideoxy‐3:4‐O‐isopropylidene‐D ‐mannitol. As far as we are aware, this kind of polyhydroxylated polyurea has not been previously described in the literature. The new polymers were characterized by standard methods (elemental analyses, gel permeation chromatography, IR, and NMR). The polyurethanes were hydrolytically degradable under physiological conditions, in contrast with less‐hydrophilic linear polyurethanes previously described. The thermal properties of the novel polymers were investigated by thermogravimetric analysis and differential scanning calorimetry. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Surface characterization of polybutadiene and natural rubbers oxidized by silver(II)

Silver (II) ion is a powerful oxidizing mediator that was used for surface modification of vulcanized polybutadiene rubber (BR) and natural rubber (NR) through mediated electrochemical oxidation (MEO). Scanning electron microscopy (SEM) pictures showed that surface morphology of the oxidized rubbers was changed so that some cracks and holes appeared on the surface in macroscopic scale. This is possibly due to chain scission caused by alkane group formation which is in turn in accordance with the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra. The amounts of hydroxyl and carbonyl type surface functional groups were also increased in both oxidized rubbers. The results obtained by atomic force microscopy (AFM) showed that the surface roughness for both rubbers was changed significantly from nano- to micro-scale. Energy dispersive X-ray analysis (EDXA) expresses that surface concentration of atomic oxygen for both BR and NR was increased significantly. Also surface polarity of the treated rubbers was enhanced based on contact angle measurements leading to a higher hydrophilicity. Finally it was found that silver(II) has a somewhat greater oxidation impact on the surface of natural rubber than polybutadiene rubber.     

Studies on thermoplastic polyurethanes based on new diphenylethane-derivative diols. II. Synthesis and characterization of segmented polyurethanes from HDI and MDI

Various new thermoplastic segmented polyurethanes were synthesized by a one-step melt polymerization from aliphatic-aromatic α,ω-diols containing sulfur in the aliphatic chain, including 4,4′-(ethane-1,2-diyl)bis(benzenethioethanol), 4,4′-(ethane-1,2-diyl)bis(benzenethiopropanol) and 4,4′-(ethane-1,2-diyl)bis(benzenethiodecanol) as chain extenders, hexane-1,6-diyl diisocyanate (HDI) or 4,4′-diphenylmethane diisocyanate (MDI) and 20-80 mol% poly(oxytetramethylene)diol (PTMO) with molecular weight of 1000 g/mol as a soft segment. The reaction was conducted at the molar ratio of NCO/OH = 1 and 1.05, and in the case of the HDI-based polyurethanes in the presence of dibutyltin dilaurate as a catalyst. The effect of the diisocyanate used on the structure and some physicochemical, thermal and mechanical properties of the segmented polyurethanes were studied. The structures of these polyurethanes were examined by FTIR and X-ray diffraction analysis. The thermal properties were investigated by differential scanning calorimetry and thermogravimetric analysis. Shore hardness and tensile properties were also determined. All the synthesized polymers showed partially crystalline structures. The MDI-based polyurethanes were products with lower crystallinity, higher glass-transition temperature (T_g) and better thermal stability in comparison with the HDI-based ones. The MDI series polymers also exhibited higher tensile strength (up to ∼36 MPa vs. ∼23 MPa) and elongation at break (up to ∼3900% vs. ∼900%), but lower hardness than the analogous HDI series polyurethanes. In both series of the polymers an increase in PTMO soft-segment content was associated with decreased crystallinity, T_g, hardness and tensile strength. An increase in PTMO content also involved an increase in elongation at break.