盾构管片专用胶的研制及应用

以端羧基液体丁腈橡胶、环氧树脂、增稠剂、着色剂等为主要材料,研制了一种盾构管片专用的改性环氧树脂胶粘剂。通过将三元乙丙橡胶密封条和丁腈软木衬垫粘接在盾构管片上,有效地解决了盾构管片的渗水和安装问题。实验结果表明,制备的胶粘剂拉伸强度和剥离强度均满足设计要求,具有强度高、耐水性和耐老化性强等优点。     

Nano- and bulk-tack adhesive properties of stimuli-responsive, fullerene-polymer blends, containing polystyrene-block-polybutadiene-block-polystyrene and polystyrene-block-polyisoprene-block-polystyrene rubber-based adhesives

Nano-tack (measured using AFM) and bulk-tack adhesive forces of blends of C₆₀ and either polystyrene-block-polybutadiene-block-polystyrene (SBS) or polystyrene-block-polyisoprene-block-polystyrene (SIS) triblock copolymer pressure sensitive adhesives were measured after exposure to white light irradiation. The nano-tack adhesive forces in C₆₀-SIS/SBS were found to decrease with increasing C₆₀ concentration and exposure time, approaching the value for 100% polystyrene, providing an indication that significant surface hardening and crosslinking of the soft isoprene and butadiene phases occurs in the presence of C₆₀. Films produced during the study were smooth, having low RMS surface roughness, and showed nanoscale phase separation between the soft (diene) and hard (styrene) segments. This phase separation disappeared after addition of C₆₀ sensitizer and white light irradiation. Bulk adhesive measurements (tack and peel strength) showed a similar trend with C₆₀ concentration and exposure time, and in irradiated systems containing as little as 0.2 wt% C₆₀, a significant decrease in adhesion was observed. Estimated T_g (measured using DMA, shear mode) of the soft-block shifts to higher temperatures (increasing by 30-40 °C), and high gel fractions were obtained, indicating the presence of chemically crosslinked networks.     

Poly(ether-ester)s modified with different amounts of fumaric moieties

A series of novel poly(ether-ester)s modified with fumaric moieties is synthesized by transesterification in the melt of dimethyl terephthalate (DMT), dimethyl fumarate (DMF), 1,4-butanediol (BD) and poly(tetramethylene oxide) (PTMO, M?_n=1000 g/mol). The effect of the introduction of double bonds into both the hard and soft segments and their content on the structure and the thermal and rheological properties of the synthesized polymers are investigated. The introduction of double bonds into the polymer main chains increases the molecular weight of the copolyesters, but reduces the crystallinity of the hard segments and related properties such as modulus and hardness. The presence of double bonds improves the high temperature properties and thermal stability, especially the thermo-oxidative one, lowers the melting and crystallization temperature and increases the glass transition temperature. The incorporation of fumaric moieties into the macrochains improves the adhesive strength of the polymer to a metal surface.     

Effect of annealing on phase separation and mechanical properties of epoxy/ATBN adhesive

Amine-terminated butadiene acrylonitrile (ATBN) was applied as curing agents for diglycidyl ether of bisphenol A epoxy resin without any accelerating agent. ATBN weight percentage of 59–82 wt% was used, so that the soft ATBN domains in the cured samples formed a continuous phase, while the hard epoxy domains formed a discontinuous phase. Mechanical properties were tested in the means of strain-stress and adhesive strength. The results showed that the samples had excellent toughness at temperatures above the flexible segment glass transition temperature (T_g1), and it was well maintained after annealing at 150 °C. However, adhesive strength of the annealed sample decreased dramatically when the testing temperature was close to the rigid segment glass transition temperature (T_g2). It was observed that (T_g2) decreased and phase separation became weaker after the annealing. Real-time Fourier transform infrared (FTIR) measurement indicated that this phenomenon was related to the disassociation of hydrogen bonding within the hard domain caused by the increased mixing of the hard segments into the soft domains by the high temperature annealing. It was confirmed by transmission electronic microscope (TEM) test.     

Increasing single-lap joint strength by adherend curvature-induced residual stresses

Single-lap joint (SLJ) geometry is the most widely used type of adhesive joint geometry. In this joint, peel stresses occur at the overlap ends due to load eccentricity and the presence of shear-free adhesive termination surfaces. These peel stresses, along with the transverse tensile stresses which occur along the overlap longitudinal axes, and adhesive shear stresses, ultimately cause joint failure. Obviously, reductions in these stresses should result in higher joint strength and increased load capacity. To this end, we exploited elastic spring-back capability of (steel) metal adherends by initially forming curved segments of varying arc lengths and radii at overlap ends. These adherends with curved-end sections were then bonded in single-lap configuration, simply by applying sufficient bonding pressure to elastically flatten the curved segments to result in typically flat overlap sections subsequent to adhesive cure and the removal of bonding pressure. Since the elastic adherend overlap ends tend to revert back to their initial curved form, they exert compressive residual stresses on the adhesive layer in the overlap end regions. We determined that the compressive residual stresses induced in this fashion considerably increased the load capacity of SLJs subjected to tension.     

Microscopy and laser diffraction investigation of block copolymers used as adhesives

In a previous paper, we established a relationship between the adhesive properties and the chain characteristics of ABA poly(styrene-b-isoprene) block copolymers (or SIS). Only copolymers which do not easily undergo phase separation give joints with high tensile lap-shear resistance. By optical and electron microscopy, as well as by laser diffraction, we have now studied the structure of a series of SIS copolymers. We found that a random distribution of small polyisoprene noduli in the polystyrene matrix effectively exists in SIS which show good adhesive properties.     

Numerical and experimental approach to testing the adhesive properties of modified polymer blend based on EVA/PMMA as coatings for optical fibers

The adhesive properties of polymer blends based on poly(ethylene-co-vinyl acetate) (EVA) and poly(methyl methacrylate) (PMMA) were studied. Two samples were prepared, whereby one kind was a physically mixed blend of commercial polymers in a solution of toluene and the other was a blend with EVA-g-PMMA polymer in a toluene solution, produced via in situ free radical polymerization using redox system initiators. A scanning electron microscopy (SEM) revealed the improved microstructure that was achieved blending with graft polymer that could also be seen by FTIR spectral analysis. Optical fibers were glued together using both of the solutions and subjected to a micro mechanical testing machine. The adhesion test showed that the graft copolymer had enhanced mechanical properties as an adhesive than the physical polymer blend. Optical microscopy of the samples after the adhesion test enabled the determination of the type of adhesive failure. Image analysis of the SEM micrographs was used to determine an area of the contact surface, and characterization microstructure. These results were then implemented in a numerical simulation that demonstrated the influence of microstructure on the adhesive properties showing the stress distribution for both samples. The main aim of obtaining an adhesive with uniform structure, great miscibility of the polymers, and good mechanical and adhesive properties was achieved and a numerical model was established that can be used in selecting the adhesive.     

Cytotoxicity,genotoxicity and antibiofilm activity on Streptococcus mutans of an experimental self-etching adhesive system containing natural Butia capitata oil

This study evaluated the biocompatibility and antibiofilm effects on Streptococcus mutans of an experimental self-etching adhesive system formulated with a natural vegetable product. The cytotoxicity of Clearfil Protect Bond (CPB), Clearfil SE Bond (CSEB), Adper SE Plus (AP), an experimental adhesive containing Butia capitata oil (EA) and an oil-free experimental adhesive as control (CA) was tested on 3T3/NIH mouse fibroblasts. Genotoxicity was indicated by micronuclei formation, and cell alterations were analyzed using light microscopy. To evaluate the effect of the adhesives on S. mutans biofilm, biomass samples were collected for dry weight and bacterial viability analyses, and the pH of the culture media was determined daily as an indicator of biofilm acidogenicity. The CA primer and EA uncured bond adhesive were the least toxic. No statistical difference was observed between EA and the untreated control, and EA showed similar effect to CPB. These findings suggest EA is biocompatible and presents activity against S. mutans biofilm.     

快速固化聚氨酯热熔胶的制备及性能研究

以4,4’-二苯甲烷二异氰酸酯(MDI)、甲苯二异氰酸酯(TDI)和1,4-丁二醇为硬段,聚四氢呋喃二醇(PTMG) 为软段,制备了一系列快速固化的反应性聚氨酯热熔胶,考察了-NCO基团含量、异氰酸酯指数及二异氰酸酯类型对粘接性能的影响。     

硬段含量对水性聚氨酯软段结晶性能的影响

以异佛尔酮二异氰酸酯、六亚甲基二异氰酸酯、聚己二酸丁二醇酯为主要原料合成了水性聚氨酯(WPU),通过FT-IR、DSC、XRD、SEM表征手段,研究了硬段含量对软段结晶性及WPU粘结性能的影响。研究表明,随着硬段含量的增加,WPU分子链上氨基甲酸酯键之间的氢键化程度提高,软硬两相相混严重,WPU软段结晶熔融焓变小,熔融温度变低;结晶衍射峰变弱,软段结晶性变差;粘结性能测试表明,在硬段含量较低时,聚氨酯体现出良好的结晶性能,初粘性较好。     

Interfacial failure analysis of functionally graded adhesively bonded double supported tee joint of laminated FRP composite plates

This paper deals with three-dimensional non-linear finite element analyses to assess the structural behavior of adhesively-bonded double supported tee joint of laminated FRP composites having embedded interfacial failures. The onset of interfacial failures is predicted by using Tsai–Wu coupled stress failure criterion with pre-determined stress values. The concept of fracture mechanics principle is utilized to study the sustainability of the tee joint having interfacial failures pre-existed at the critical locations. Individual modes of the strain energy release rates (SERR) G_I, G_II and G_III, are considered as the damage growth parameters and, are evaluated using the Modified crack closure integral (MCCI) technique based on the concept of linear elastic fracture mechanics (LEFM). Based on the stress analyses, it has been observed that the interfacial failures in tee joint structure trigger at the interface of base plate and adhesive layer from both ends of base plate. Depending on the SERR magnitudes, it has been noticed that the interfacial failure propagates under mixed mode condition. Therefore total SERR (G_T) is considered as the governing parameter for damage propagation. Furthermore, efforts have been made to retard damage propagation rate by employing functionally graded adhesive (FGA) instead of monolithic adhesive material. Series of numerical simulations have been performed for varied interfacial failure length in functionally graded adhesively bonded double supported tee joint structure in order to achieve the significant effect of FGA with various modulus ratios on SERR. Material gradation of adhesive indicates significant SERR reduction at the incipient stage of failure which necessitates the use of functionally graded adhesive for the tee joint and prolong the service life of the structure.     

Evolution of crack path and fracture surface with degradation in rubber-toughened epoxy adhesive joints: Application to open-faced specimens

The crack path and fracture surface in the mixed-mode fracture of two different rubber-toughened epoxy adhesives were evaluated using double-layered open-faced double cantilever beam (ODCB) specimens in which the primary adhesive layer had been environmentally aged. The crack path in the mixed-mode fracture of unaged ODCB specimens was unexpectedly in the secondary adhesive layer, and several hypotheses were examined to explain this. It was concluded that a reduced residual stress in the secondary adhesive layer produced stable crack growth in the secondary layer instead of the expected path in the primary layer. The average crack path depth, fracture surface roughness and maximum elevation in the fracture surface profiles were then measured using optical profilometry as a function of the degree of aging. The results showed a strong relationship between all these parameters and the critical strain energy release rate, G_cs, irrespective of the type of adhesive. In the case of adhesive A where significant irreversible degradation was observed, all these parameters varied approximately linearly with G_cs. In the case of adhesive B, aging did not result in permanent degradation (G_cs was unchanged) and so all these fracture surface parameters also remained unchanged after aging. The results indicate that quantifying fracture surface parameters as a post-failure analysis can be of use in the estimation of the fracture toughness at which a practical joint fails.     

Adhesion Properties of Acrylic Copolymers Modified with Si-Containing Copolymer

We made clear the cause of the increase in peel strength of pressure sensitive (PS) adhesives as a function of contact time, and investigated how to modify PS adhesives to maintain a low and constant peel strength for a long time. It was found that polar groups in the adhesive orient to the interface between the adhesive and the (stainless steel) metal substrate (SUS 304) so as to minimize interfacial free energy during adhesion, and the orientation increased affinity between the adhesive and the metal material and increased the peel strength as a result. The use of modifier which contained both P(MMA-co-SiMA) and PDMS showed an excellent modification effect, although modification with only PDMS or P(MMA-co-SiMA) was not sufficient. It was suggested that PDMS which migrated to the surface was extended uniformly over the surface by PDMS segments of P(MMA-co-SiMA) and that the enriched layer of PDMS on the adhesive surface worked as a barrier to prevent the orientation of polar groups in bulk. Therefore, low and constant peel strength could be achieved.     

Fabrication and evaluation of one-component core/shell structured latex adhesives containing poly(styrene) cores and poly(acrylate) shells

A one-component, non-crosslinked, and ambient temperature-cured core/shell (CS) structured waterborne poly(styrene-acrylate) (PStA) latex adhesive was prepared by two-stage seeded emulsion polymerization. The first-stage polymers were non-polar styrene-based copolymers with T_gs ranging from 86 °C to 41 °C and the second-stage polymer was polar acrylate-based copolymer having a T_g of 8 °C. The effect of latex particle morphology and film microstructure on the CS structured PStA latex adhesive was examined by evaluating film thermal properties and mechanical performance. The results have shown that incorporation of soft shell polymers into hard core polymers can improve adhesive properties without compromising film-forming ability. Wood adhesive performances of latex adhesive were measured by shear strength and boiling water resistance of glued wood blocks. The utilization performances of the one-component CS structured PStA latex adhesive were found to largely depend on CS morphological character and the interfacial compatibility between various polymeric constituents, demonstrating that fabrication of CS latex particles provides a promising approach to realize high-performance latex adhesives.     

Adhesion Properties of Acrylic Copolymers Modified with Si-Containing Copolymer

We made clear the cause of the increase in peel strength of pressure sensitive (PS) adhesives as a function of contact time, and investigated how to modify PS adhesives to maintain a low and constant peel strength for a long time. It was found that polar groups in the adhesive orient to the interface between the adhesive and the (stainless steel) metal substrate (SUS 304) so as to minimize interfacial free energy during adhesion, and the orientation increased affinity between the adhesive and the metal material and increased the peel strength as a result. The use of modifier which contained both P(MMA-co-SiMA) and PDMS showed an excellent modification effect, although modification with only PDMS or P(MMA-co-SiMA) was not sufficient. It was suggested that PDMS which migrated to the surface was extended uniformly over the surface by PDMS segments of P(MMA-co-SiMA) and that the enriched layer of PDMS on the adhesive surface worked as a barrier to prevent the orientation of polar groups in bulk. Therefore, low and constant peel strength could be achieved.     

Effect of hot humid environmental exposure on fatigue crack growth of adhesive-bonded aluminum A356 joints

In this study, the effect of hot humid environmental exposure prior to and after adhesive curing on the fatigue crack growth (FCG) behavior of adhesive-bonded aluminum A356 joints was investigated by using single-edge notch bend (SENB) specimen. The results showed that while the exposure after adhesive curing had a significant effect on the FCG resistance of the joints, the exposure of the assembled joints prior to adhesive curing had a relatively small influence. In addition, the effect of load ratio R on the FCG behavior of the exposed joints was studied. The results showed that the FCG of the exposed joints is more sensitive to load ratio R than that of the unexposed joints.     

A thermally responsive, rigid, and reversible adhesive

In this paper we present the development of a unique self-adhesive material that, unlike conventional adhesives, maintains a high degree of rigidity at the “adhesive” state while possessing the ability to easily de-bond upon heating. Consequently, the material is both a rigid and a reversible adhesive. The material is an initially miscible blend of poly(?-caprolactone) (PCL) and diglycidyl ether of bisphenol-A/diaminodiphenylsulfone (DGEBA/DDS) epoxy, processed to a unique morphology via polymerization-induced phase separation (PIPS). The fully cured material features a biphasic, “bricks-and-mortar” morphology in which epoxy forms highly interconnected spheres (“bricks”) that interpenetrate with a continuous PCL matrix (“mortar”). When heated to melt the PCL phase (60 °C < T < 200 °C), the epoxy bricks remain rigid due to the high epoxy T_g (>200 °C) while PCL liquefies to become a melt adhesive. Moreover, the PCL liquid undergoes microscopic dilational flow to wet the sample surfaces due to its high volumetric expansion in excess to epoxy bricks expansion, a phenomenon we term “differential expansive bleeding” (DEB). Remarkably, the samples remain rigid at this state and their surfaces become covered by a thin layer of PCL now able to wet, and subsequently bond through cooling, to a variety of substrates. We observe high bonding strengths, which we attribute to a combination of good wetting and subsequent formation of a thin layer of crystalline PCL with high cohesive strength upon cooling. This adhesive layer can be melted again by heating (T > T_m) to easily de-bond and subsequent rebonding capacity was demonstrated, indicating repeated availability of PCL melt adhesive to the surface by the DEB mechanism.     

Crack-growth behavior of epoxy adhesives modified with liquid rubber and cross-linked rubber particles under mode I loading

The crack-growth resistance (R-curve) of bulk single-edge notch bend (SENB) and adhesively bonded double cantilever beam (DCB) specimens was investigated under mode I loading conditions using two types of rubber-modified epoxy adhesive: one was a liquid rubber (CTBN)-modified adhesive and the other was a cross-linked rubber particle (DCS)-modified adhesive. As a result, for both the SENB and DCB specimens, the gradient of the R-curve for the DCS-modified adhesive was steeper than that for the CTBN-modified one, however, the difference in fracture toughness between DCS- and CTBN-modified adhesives is smaller for DCB than for SENB specimens. To elucidate such behavior, crack-growth simulation based on Gurson's model was conducted, where the DCS- and CTBN-modified adhesives were characterized by both the initial void fraction and nucleation. The difference in the behavior of R-curves was also observed in simulations. Moreover, it was found that the difference in fracture surface roughness observed by SEM for both adhesives correspond to the variation in R-curves.     

Scanning probe microscopy study of dynamic adhesion behavior of polymer adhesive blends

Scanning Probe Microscopy (SPM) has been utilized to study the adhesive behavior of a blend of poly(ethylene propylene) (PEP) and the n-butyl ester of abietic acid. This blend is a model for a pressure sensitive adhesive (PSA). Force-distance measurements with simultaneous X-modulation gave information on both lateral and normal force during loading and unloading. This was a key advantage of the approach. The mechanism of adhesive failure has been elucidated by comparing the dependence of pull-off force (F_pull-off) and oscillating lateral force (F_lateral) on velocity of loading/unloading and by studying the change with velocity in the loss of effective contact area during debonding. Change in contact area with time was inferred from change in the rms lateral force. The velocity dependence of F_lateral indicates that its magnitude is strongly influenced by both contact time and the presence of tackifier. In contrast, the velocity dependence of F_pull-off is controlled by both the loading and unloading processes. While the adhesive behavior of the polymer (PEP) was mainly controlled by chain stretching during the unloading process, the adhesive performance of the tackifier enriched surface (PEP/60) was determined by the loading process at 10-50 nm/s loading velocity and by the unloading process at 100-1000 nm/s velocity.     

Hygrothermal degradation of two rubber-toughened epoxy adhesives: Application of open-faced fracture tests

The absorption/desorption properties of two commercial, toughened epoxy adhesive systems were evaluated gravimetrically, and by X-ray photoelectron spectroscopy (XPS) and dynamic mechanical thermal analysis (DMTA). Fracture tests on degraded open-faced DCB specimens showed that these two adhesive systems have very different degradation behaviors. The steady-state critical strain energy release rate, G_cs, of an adhesive system 1 decreased rapidly with an exposure time in various hot-wet environments, reaching a relatively low value that was stable for over one year, while that of adhesive system 2 remained unchanged for more than one and a half years. A degradation mechanism which accounts for the different characteristics of the two adhesive systems was proposed. A model of fracture toughness degradation, analogous to Fick’s law, was then used to characterize the fracture toughness loss in an adhesive system 1, and the effects of temperature, RH and water concentration were evaluated. The results illustrate the wide variation in water absorption behaviors that can exist among toughened epoxy adhesives, and show how these differences relate to the degradation of fracture strength. The data were also used to assess the applicability of an exposure index (EI), defined as the integral of relative humidity over time, as a means of characterizing an aging history. The fracture strength degradation was measured after aging to achieve a range of EI values, and it was found that the strength loss was independent of the time-humidity path for sufficiently large EI.