Rubber Through Covalent

Subscriber access provided by UOW Library

Article

Integration of Peroxide-Cured Rubber/Rubber Through Covalent Grafting of a Thiol-Linked Molecular Layer Jing Sang, Sumio Aisawa, Takahiro Kudo, Hidetoshi Hirahara, and Kunio Mori Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b00969 • Publication Date (Web): 31 May 2016 Downloaded from http://pubs.acs.org on June 1, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Integration of Peroxide-Cured Rubber/Rubber Through Covalent Grafting of a Thiol-Linked Molecular Layer Jing Sang, *† Sumio Aisawa, † Takahiro Kudo, ‡ Hidetoshi Hirahara† and Kunio Mori, †‡ †

Department of Frontier Materials and Function Engineering, Graduate School of Engineering,

Iwate University, 4-3-5, Ueda, Morioka 020-8551, Japan ‡

Sulfur Chemical Institute, 210, Collabo MIU, 4-3-5, Ueda, Morioka 020-0066, Japan

ABSTRACT:

A simple, nonfluid, and direct adhesion method was developed to adhere cured rubber/rubber via grafting of a molecular layer of a triazine-based silane coupling agent without any pretreatment. During peroxide curing, oxide functional groups that can react with silanol groups were automatically fabricated on the surface of acrylonitrile–butadiene rubber (NBR) during primary processing at different curing temperatures. After the molecular layer was grafted onto the cured rubber surface, nonfluid adhesion between the cured NBR surfaces was induced. An NBR/NBR joined body was obtained and exhibited high adhesion strength with cohesive failure.

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 36

The presented method is rapid, inexpensive, environmentally friendly, and can resolve the persistent problems of spew, extra adhesive, and rugose interface in the “fluid adhesion” of adhesive adhesion and vulcanization bonding processes. In addition, this method does not require secondary processing for inducing the formation of functional groups, and should therefore, be particularly valuable in industrial adhesion applications.

KEYWORDS: NBR, Peroxide curing, Triazine, Nonfluid adhesion, Direct adhesion, Molecular layer

1. INTRODUCTION With the rapid development of micro- and nanoelectronics, the use of hybrid integration to assemble electronic devices on flexible substrates of plastic and rubber materials has become important in a wide range of industrial applications 1. The adhesion between pairs of parts is indispensable in the fabrication of integration devices with high reliability 2. As an adhesion technology of polymers, adhesive adhesion and the vulcanization bonding process are used in a growing number of industrial applications

3, 4

. The complexity of the vulcanization bonding

process lies in the fact that the vulcanization of rubber and the curing of an adhesive previously coated onto solid adherend materials such as metal, cured resin, and rubber surfaces must occur simultaneously during a single molding step 5. During this step, the uncured resin or rubber flows into the mold and contacts the adherend surface. In case of adhesive adhesion, the adhesive can also flow onto the surfaces of the adherend materials. Here, we refer to these methods as “fluid adhesion”. Such methods can increase the contact area of the adherent materials during the flow process, thereby enhancing interfacial bonding strength. These fluid adhesion methods provide


2

Page 3 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


excellent productivity and convenience because the shaping, curing, and adhering processes are achieved in a single step 6. Although adhesion strength can be promoted through high surface roughness, surface wettability is more important 7. Additionally, fluid adhesion should solve problems such as spew, extra adhesive 8, and rugose interfaces

9

(as shown in Figure 1(a) and

(b)). In case of microparts, large-scale parts, and complex parts with three-dimensional shapes, fluid adhesion is difficult. In this scenario, instead of “fluid adhesion,” a “nonfluid adhesion” technology (as shown in Figure 1(c)) between the elastomer and nonfluid materials appears to be a promising technology for improving the production efficiency, reducing costs, and imparting multifunctionality. Adhesion mechanisms are known to depend on the surface characteristics of materials

10

. In

case of nonfluid adhesion, hydroxy and other hydrogen-bonding dipolar functional groups were first introduced on plastic and rubber surfaces via secondary surface treatments such as plasma 11, 12

, UV, and corona charge 13 after the shaping process to obtain active surfaces. A surface primer

was then grafted to react with the adherents

14-17

. Recently, we reported a method of molecular

adhesion via grafting of a triazine-based silane coupling agent onto the surfaces of materials to facilitate adhesion

18-21

after the introduction of reactive functional groups such as hydroxy

groups. The aforementioned methods of introducing functional groups are effective on flat surfaces; however, for complex parts with three-dimensional shapes, these methods are difficult to implement and cannot be used with some parts. In addition, these physical modification methods of plasma and corona treatments cannot create permanent oxide groups

22

because the

functional groups created on the substrate surfaces would vary with time and environmental changes 23.


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 36

In the peroxide curing process, the surfaces of some organic materials such as acrylonitrile– butadiene rubber (NBR) undergo insufficient curing reactions because of contact with oxygen under normal atmospheric pressure

24, 25

. In case of these materials, peroxide radicals react with

oxygen and provide polymer peroxide radicals (POO•s)

26, 27

; the subsequent hydrogen

abstraction reaction from the hydrocarbon chains of polymer hydroperoxide (POOH) 28, 29 results in disproportionation decomposition, thereby providing polymer end aldehydes (P1CHO) and polymer end alcohols (P2CH2OH)

24

. Therefore, in accordance with the active use of peroxide

curing under contact atmosphere, hydroxy groups are generated by the curing process. The reaction between hydroxy groups and triazine-based silane coupling agents is important for introducing active thiol groups onto the cured rubber surface. The nonfluid adhesion between cured NBR is achieved through single-step surface modification via grafting of a thiol-linked molecular layer. In this study, we use NBR peroxide curing to produce a functionalized surface as the primary process and subsequently treat the surface of the cured NBR with 6-triethoxysilylpropylamino1,3,5-triazine-2,4-dithiol monosodium salt (TES). The TES properties of high heat stability and strong adhesion to different substrate materials are important factors for the operation of electronic devices. Its ethoxysilylpropylamino groups adhere to the hydroxy groups of the substrate, and its thiol functional groups can form a bridging link to metal ions on the substrate 30-32

. Here, a thiol-linked surface was prepared on cured NBR. The surface functional groups

were characterized by X-ray photoelectron spectroscopy (XPS) surface analysis, and the physical properties of the cured NBR surface were investigated. The surface characteristics enabled the TES-linked NBR to overlap and contact each other, resulting in nonfluid adhesion.


4

Page 5 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2. EXPERIMETAL 2.1. Materials and Reagents NBR (acrylonitrile: 35%, N230S, JSR Co.) was used in this study. The NBR compounds were prepared using an open two-roll mill to mix NBR (100 phr) and additives carbon black (50 phr), stearic acid (1 phr), and ZnO (5 phr) as a stabilizer. Dicumyl peroxide (DCP, reagent grade) was added to the aforementioned base compounds as a curing agent. Polyamide (PA6, 2015B, 230 °C/451 kPa, Ube Industries, Ltd.) was used as a contact material during the NBR molding process. TES was used a surface treatment agent and molecular adhesive (Sulfur Chemical Institute Co., Ltd.) to graft a molecular layer onto cured NBR. 2.2. Compounding and Curing After the open-mill mixing process, cured NBR was prepared using a molding process involving contact with PA6 films in a molding cabinet at 140, 150, 160, 170, or 180 °C for 30 min (8MPa); DCP was used as a curing agent. After the molding process, the cured NBR samples were immediately removed from the molding cabinet. The surfaces and cut-surface samples of the cured NBR rubbers were prepared for analysis as 1 × 2 × 5 mm3 cuboids with six surfaces. One surface contacted with the mold of PA6 was the surface obtained by curing; the others were cut surfaces (interior) obtained by cutting, which allowed us to evaluate the characteristics of the cured NBR bulk. Before surface analysis, the PA6 films were peeled from the cured NBR samples after the samples had been maintained under vacuum for 24 h. 2.3. Surface Modification and Adhesion


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 36

The obtained NBR was immersed in TES (0.1 M) aqueous solution at 25 °C for 10 min, and then dried in air. The products were placed into oven at 120 °C for 10 min and then cooled to 25 °C, washed with alcohol to remove the unreacted TES on the NBR surfaces, and dried in air. The resulting NBR samples were used to perform adhesion process. The two TES-linked NBR samples were superposed upon each other to take adhesion process under hotpress. 2.4. Characterization and Tests Static contact angles were measured using an optical contact angle measuring instrument (Kyowa Interface Science DM-501); the measurements were performed with 1 µL distilled water at 25 °C. The reported values are the average contact angle for five distilled water drops at different positions in one sample. The surface chemical compositions and structures of cured NBR rubbers were analyzed by XPS (PHI QUANTERA ESCA system) using a Multi Technique spectrometer, a focusing monochromator (ULVAC-PHI Inc.), and an Al Kα X-ray source with a 100 µm × 100 µm spot size. Pass energies of the analyzer were 69 eV for high-resolution scans at 300 W. The angleresolved measurements were conducted at electron takeoff angles of θ = 15°, 30°, 45°, 60°, and 75°. The analysis chamber remained at 3.0 × 10−6 Pa during the whole XPS measurement range under charge neutralization. The XPS spectra were subjected to Shirley background subtraction formalism, and the data were calibrated using the saturated C1s peak at 284.8 eV during chemical-bonding-state assignments. The full width at half maximum (FWHM) of the C–C/C–H component was allowed to vary freely; the other components were then fixed to adopt this value.


6

Page 7 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


During all curve-fitting treatments, Gaussian–Lorentzian lines of variable proportion were used; the XPS experimental curve fitting was performed using the Multipak software. Friction coefficients of cured NBR rubber surfaces were measured using a friction tester (FRICTION PLAYER FPR-2000, Rhesca Co., Ltd., Japan). The tests were sliding friction tests between an Al plane indenter and a disk of one of the studied rubber samples; the tests were performed under dry conditions at 25 °C. Cycle tests were carried out by rotating the plane under the sliding Al indenter with different loads ranging from 5 g to 50 g. The reciprocation measurement mode was 12 rpm, the cycle diameter was 10 mm, and the linear velocity was 1.2566 cm/s. The adhesion strength of the NBR/NBR joined body was determined using a peel test. The NBR/NBR joined body was constructed using similarly treated rubber-strip test pieces (width: 10 mm). The peeling tests were carried out using a tensile machine (JIS K-6854-4) according to the T-type peeling test at a crosshead speed of 100 mm/min at 25 °C. After the peeling tests, the morphologies of the failure interfaces were measured by scanning electron microscopy (SEM, VE8800, KEYENCE, Japan). For the NBR/NBR joined body with adhesion strength of cohesive failure, the interface morphologies of the NBR/NBR adhesion samples were characterized by transmission electron microscopy (TEM, JEM-2100, JEOL Japan, operated at 200 kV). Samples for TEM measurements were prepared by FIB milling to enable high-magnification imaging of the NBR/NBR adhesion interfacial layer. Dynamic mechanical analysis (DMA) was carried out using a DMA 8000 dynamic mechanical analyzer manufactured by PerkinElmer Japan Co., Ltd.; the analyses were performed from


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 36

−100 °C to 60 °C at a heating rate of 4 °C/min and at a fixed frequency of 10 Hz in the doublecantilever-deformation mode. Curves of tan δ as a function of temperature were recorded.

3. RESULTS AND DISCUSSION 3.1. Surface Analysis of Cured NBR Surface properties are important in materials-joining techniques such as joint welding or adhesive adhesion. In particular, in a nonfluid adhesion (here, cured NBR) process, the materials of both adherends are not fluid; the surface properties of wettability, functional-group type and concentration, and surface roughness need to be clarified. 3.1.1. Contact angles of cured NBR The contact angles of NBR surfaces and cut surfaces cured at different temperatures were measured; the results are shown in Figure 2(a). The surface contact angle of NBR cured at 140 °C was 90°. When the curing temperature was increased to 180 °C, the contact angle decreased to 82°. By contrast, the cut-surface contact angle of cured NBR was static at approximately 95 °C. Wettability is known to be governed by the structure and composition of the surface 24. Highly polar functional groups on the surface will result in better wettability and low distilled water contact angles. 3.1.2. Chemical analysis of cured NBR XPS was used to analyze the chemical composition of the cured NBR surfaces. Figure 2(b) and (c) presents the variation in the N and O elemental concentrations, respectively, with increasing depth from the topmost surface of NBR surfaces cured at different temperatures. With increasing


8

Page 9 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


surface measurement depth, the concentrations of N increase, but those of O decrease, irrespective of the curing temperature. This behavior is due to the reaction between the POO•s of NBR and oxygen under an air atmosphere. Oxygen is more abundant on the topmost surface than in the interior; consequently, oxidation products are more abundant on the topmost surface. The increasing N concentration with depth is due to the degradation of the nitrile groups of NBR surface with the oxidation. The reaction mechanism and surface chemical structures were investigated on the basis of deconvolution of high-resolution XPS spectra. In addition to elemental composition changes, we also observed significant differences in the XPS high-resolution spectra among the NBR surfaces cured at different temperatures. Table 1 shows the deconvolution results for the C1s XPS spectra, which were investigated for further confirmation of the chemical composition of the cured NBR surfaces. The escape depths were calculated using an electron attenuation length (λ) of 2.7 nm

33, 34

. Take-off angles (θ) of 15°,

30°, 45°, 60°, and 75° were used. The corresponding calculated escape depths (which are equal to λsinθ) of photoelectrons near the surface were 0.7 nm, 1.4 nm, 1.9 nm, 2.3 nm, and 2.6 nm, respectively

35, 36

. As a result, the C1s spectra for cured NBR surfaces were separated into six

peaks: the peak at 284.7 eV is attributed to *C–C/*C–H; the peak located at 285.4 eV is assigned to–*CH2CH(CN)*CH2–; the –*CH(CN) and –*CHOH peaks are too similar for deconvolution and are located together at 286.3 eV; and the peaks at binding energies of 286.6 eV, 278.3 eV, and 288.8 eV are due to >*CN, >C=O, and –COOH, respectively. During the hotpress process, thermal degradation of the acrylonitrile phase in NBR is initiated by hydrogen abstraction from carbon atoms to polymer radicals on the NBR surfaces. This abstraction generates radicals that, in the presence of oxygen, lead to the formation of carbonyl and hydroxyl products

37

. The

relative concentrations of the different carbon species were 5.7 at.% >*CN and 2.5 at.% –


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 36

*CHOH on the topmost NBR surface (depth approximately 0.7 nm) cured at 140 °C. However, no >C=O or –COOH species were observed. With increasing depth from the surface, XPS analysis reveals greater concentrations of >*CN species, supporting the same conclusion that decreasing N concentration on a cured surface is due to the degradation of the NBR nitrile groups. With increasing NBR curing temperature, the concentration of >*CN decreases and that of oxide groups (–*CHOH, >C=O, and –COOH) increases. When the curing temperature was increased to 150 °C, >C=O was observed on the topmost NBR surface, and when the curing temperature was increased to 160 °C, –COOH was observed. When the curing temperature was further increased to 180 °C, the lowest >*CN concentration of 2.1 at.% and the largest oxide concentration were obtained on the topmost NBR surface. These observed decreases in the concentration of >*CN species are primarily due to increased concentrations of –COOH groups. The variation in the concentration of –COOH groups on the NBR surfaces with depth is summarized in Figure 2(d) for specimens cured at different temperatures. When the curing temperature was lower than 160 °C, –COOH was not observed on the NBR surfaces. The concentration of –COOH increased with increasing curing temperature and decreased with increasing depth. These results indicate that the oxide reaction on the NBR surface occurred through hydrogen abstraction from carbon atoms of >*CN to form >*CN radicals. Because oxygen, carbonyl, and hydroxyl products were formed, the >*CN groups were degraded to small molecules and volatilized from the NBR polymer. The oxide reaction was enhanced at high temperatures and under sufficient oxygen partial pressure. Thus, the –COOH concentration increased with increasing temperature and decreased with increasing depth because of the lack of sufficient oxygen in the NBR interior during peroxide curing.


10

Page 11 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3.1.3. Analysis of physical properties of cured NBR The contact load between the sliding indenter and the polymer surface strongly influences the surface friction coefficient (µ)

38

. For each NBR surface cured at different temperatures, as

shown in Figure 3, µ decreased with increasing contact load. For example, the µ of NBR cured at 140 °C decreased from 2.4 to 1.4 when the contact load was increased from 5 N to 50 N. The surface friction coefficient (µ), however, did not change with the contact load. The deformation underwent a transition from an elastic regime to a plastic regime with increasing applied load. This transition occurred because the surface molecular chains of NBR became adsorbing to the indenter under load during the friction process and the movement of molecular NBR chains was limited. When a higher load is applied during the sliding contact, localized compressive deformation on the NBR surface by the Al indenter will occur

38

. Thus, the actual contact area

between the sliding surface pair will increase. Moreover, as shown by the slope of the curve, when the curing temperature was 140 °C, µ increased when the load was decreased to 40 g because of the adsorption between NBR polymer chains and the Al indenter. When the curing temperature was 180 °C, µ increased after the load was decreased to 10 g. We attributed this behavior to differences in the polymer Mc-molecular weights for NBR surfaces cured at different temperatures. Additionally, in case of nonfluid adhesion, these results indicate that the characteristics of the surface contact between NBR samples brought into contact with each other during the adhesion process will depend on the curing temperature, irrespective of surface roughness. DMA is an experimental technique that involves applying oscillation stress to a specimen (forced-vibration oscillation mode) and measuring the resulting strain developed in the sample. It can provide deep insight into the tack performance of rubber 39. Figure 4 shows the variation in


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 36

tan δ with temperature of NBR surfaces cured at 140 °C and 180 °C. As evident in this figure, the tan δ curve for the NBR surface cured at 140 °C contains four peaks at −18.8 °C, −34.6 °C, −47 °C, and −89.4 °C. A molecular cross-linking chain will increase the Tg of NBR. At Tg, a peak in tan δ that corresponds to a transition in molecular conformation from a glassy to a rubbery state is observed

37

. In case of the sample cured at 180 °C, the tan δ curve shows two peaks at

−11.3 °C and −73.1 °C. The nature of the tan δ curve is affected by polymer stiffness

40

, which

depends on the distribution of polymer molecular weight and the degree of crosslinking. Thus, the main peaks at −18.8 °C and −11.3 °C in the tan δ curves of the samples cured at 140 °C and 180 °C, respectively, reflect differences in the Mc-molecular weights of the NBR surfaces of the specimens cured at these curing temperatures; these differences in Mc-molecular weights, in turn, originate from the specimens’ different degrees of crosslinking. The other peaks represent the reaction products of terminal groups during NBR curing at lower curing temperatures. In this regard, during the nonfluid adhesion process, interfaces form more easily between NBR surfaces cured at 140 °C than between interfaces of surfaces cured at 180 °C. 3.2. Chemical Composition of Cured NBR Surfaces after Grafting of a TES Molecular Layer Figure 5a shows the contact angles of NBR surfaces cured at different curing temperatures before (bare NBR) and after TES treatment (TES-linked NBR). This figure clearly shows that the contact angles of TES-linked NBR surfaces were all higher than those of bare NBR surfaces because of the organic steric structure of TES, which can reduce the hydrophilic effect of polar groups on cured NBR surfaces.


12

Page 13 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5(b) presents the XPS survey spectra of the NBR cured at 140 °C before and after TES treatment. S2p, S2s, and Si2p peaks appear in the spectrum of the NBR surface after TES treatment. The S and Si in this sample both originate from the TES molecular adhesive. Figure 5(c) shows the C1s spectra of bare NBR surfaces and TES-linked NBR surfaces. In these spectra, the COOH peak at 288.8 eV in the spectra of the NBR surfaces cured at 160 °C, 170 °C, and 180 °C (Table 1) is absent in the spectra of samples subjected to TES treatment. The XPS results indicate that TES reacted on the specimen surfaces. Figure 5(d) shows the deconvoluted S2p curves of the XPS spectra, which were investigated for further confirmation of the chemical composition of TES-linked NBR surfaces. The sulfur spectrum consists of S2p3/2 and S2p1/2 peaks with an intensity ratio of 2:1 and a binding-energy difference of 1.2 eV according to the spin–orbit splitting effect. The S2p spectra of the TESlinked NBR surfaces contain six peaks: the peak at 162.08 eV is attributed to C=S/C–S of S2p3/2 41

; the peaks at 164.0 eV and 165.2 eV are assigned to SS/SH 42; and those at 167.0 eV and 168.2

eV are attributed to the oxidized sulfur of SOx 43. The oxidized sulfur originated from the S of the thiol groups in TES. The amount of oxidized sulfur on the surface of NBR cured at 180 °C and subjected to TES treatment was greater than that on the surface of the TES-linked NBR cured at 140 °C. These chemical compositions affect the nonfluid adhesion strength. 3.3. Nonfluid Adhesion between TES-linked NBR Figure 6 shows the influence of curing temperature on the peel strength (maximum peeling forces) of TES-linked NBR/NBR joined bodies. A substantial decrease in the peel strength was observed with increasing curing temperature. Cohesive failures in the rubbers cured at 140 °C and 150 °C were observed, and the peel strengths were 10.1 N/cm and 7.2 N/cm, respectively. In


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 36

the cases of NBR cured at 160 °C, 170 °C, and 180 °C, the TES-linked NBR/NBR joined bodies exhibited adhesive failure. When the curing temperature was increased to 180 °C, a low peel strength of 3.2 N/cm was obtained. When the NBR was cured above 160 °C, the TES-linked NBR/NBR interface after the adhesion process and peel test exhibited adhesive failure; in addition, SEM images show cohesive rupture spots on the adhesion interfaces (inset of Figure 6). These results indicate that NBR surfaces cured at temperatures from 140 °C to 180 °C after application of the TES-linked molecular layer can react with each other, forming covalent bonds. However, because of the different surface characteristics, the reactions differ; as a result, different adhesion strengths are obtained. On the basis of the analysis of the effect of curing temperature on peel strength, curing temperatures of 140 °C and 180 °C were chosen as typical comparison parameters to investigate the adhesion properties. 3.4. Adhesion of TES-linked NBR 3.4.1. Mechanism of adhesion of TES-linked NBR Figure 7 shows a schematic of the reaction between an NBR surface and TES and the adhesion process. Because TES is a sodium salt, it easily dissolves in water, thereby facilitating hydrolysis reactions. Initially, hydrolysis of the three labile groups of alkoxysilane occurs to form reactive silanol groups 44. These groups can react with oxides such as OH groups on cured NBR. At the same time, C=O and COOH groups can react with TES. However, at high curing temperatures, COOH groups dominate the NBR surface because of the degradation of >*CN groups to small molecules (see XPS analysis results in section 3.1.2). The COOH likely reacted with TES and resolved in the solvent after TES treatment. Additionally, at curing temperatures above 160 °C, CO• and COO• radicals formed on the NBR surface

24

. During TES treatment, thiol groups


14

Page 15 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reacted with these radicals on the cured NBR surface; the resulting thiol radicals (•S) then reacted with each other and/or were oxidized to SOx before the adhesion process. During the adhesion process, the thiol groups of TES did not form a chemical bond with the adherend of the same TES-linked NBR surfaces. 3.4.2. TES-linked NBR/NBR adhesion characteristics A TEM micrograph of the TES-linked NBR/NBR adhesion interface is shown in Figure 8. The dark spheres in the micrographs are the carbon black dispersed in the NBR rubber, whereas the off-white phases indicate an NBR rubber matrix. The TEM image demonstrates that cured NBR was adhered by TES. Additionally, the TES molecular layer was confirmed at the interface of TES-linked NBR/NBR; this layer was observed in the TEM image as a gray line with a width of 10 nm. Through calculations, we determined that the TES molecular structure was 1.2 nm long, 0.8 nm wide, and 0.6 nm thick and that the surface area of one molecule was 4.8 × 10−13 mm2 30. At the interface between pieces of the same rubber material, a competition arises between an interdiffusion process and a chemical reaction 45. For bare cured NBR, the mobility of polymer chains in the entangled state is drastically reduced by chain branching; the cross-linking of the rubber molecules prevents their interdiffusion. After TES treatment, the chains of the cured rubber surfaces can react with each other and interdiffusion at the rubber interface is observed. The broadening of the interfacial width causes an interconnected network in the interface, leading to strong interfacial adhesion 46. As a result, the adhesion interfacial width of TES-linked NBR/NBR is wider than the molecular size because of the interfacial reactions and interdiffusion.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 36

Figure 9 shows plots of tan δ versus temperature for bare NBR and a TES-linked NBR/NBR joined body. Here, the Tg values of the bare cured NBR rubber and the NBR/NBR joined body were −18 °C and −17 °C, respectively, whereas the Tg determined from the loss-modulus peak is −24 °C. However, additional peaks were observed at −38 °C and −44 °C in the loss-factor curves. The TES molecular layer oscillation peak was observed at −38 °C. Because the TES molecules are smaller than the NBR polymer molecules, the TES molecules oscillate at a lower temperature. In case of the bare NBR, because the sample was prepared with surfaces and therefore differs from the bulk material, the molecular oscillation occurred at a temperature lower than the Tg of bulk NBR. These results are consistent with the TEM results discussed in the previous sections. 4. CONCLUSIONS A facile method was used to adhere cured NBR by grafting a molecular layer of a TES. By effectively utilizing peroxide curing reactions on a rubber surface, we directly grafted TES onto the cured NBR surface, which subsequently underwent adhesion without a pretreatment such as plasma, UV, or corona discharge. The chemical reaction mechanisms of the NBR surface curing and adhesion between TES-linked NBR were investigated. In addition, surface physical properties were characterized through DMA and measurements of the friction coefficients. The results indicated that NBR surfaces cured at a low curing temperature (140 °C) contain more OH groups and shorter end chains compared to NBR surfaces cured at a high curing temperature (180 °C). The adhesion interface between NBR surfaces cured at 140 °C are more easily formed than NBR surfaces cured at 180 °C during the nonfluid adhesion process because of the chemical and physical characteristics. Nonfluid adhesion between TES-linked NBR (cured at 140 °C and 150 °C) was achieved, and the joined bodies exhibited high adhesion strength with cohesive


16

Page 17 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


failure in peel tests. We believe that the method developed in this work may open a new approach to adhering nonfluid solid materials. AUTHOR INFORMATION Corresponding Author *To whom correspondence should be addressed. Tel.: +81-19-621-6333. E-mail: [email protected] Funding Sources Council for Science, Technology and Innovation (CSTI); Cross-Ministerial Strategic Innovation Promotion Program (SIP); Industry-Academia-Government Collaboration Promotion Programs ACKNOWLEDGMENT This work was supported by CSTI and “Innovative Design/Manufacturing Technologies” of SIP. We gratefully acknowledge the Ministry of Economy, Trade and Industry of Japan for funding support for this research.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 36

REFERENCES (1)

Halik, M.; Hirsch, A. The potential of molecular self‐assembled monolayers in organic

electronic devices. Adv. Mater. 2011, 23, 2689-2695. (2)

Yu, W.; Peri, S. R.; Akgun, B.; Foster, M. D. Manipulation of polymer/polymer interface

width from nonequilibrium deposition. ACS Appl. Mater. Inter. 2013, 5, 2976-2984. (3)

Souid, A.; Sarda, A.; Deterre, R.; Leroy, E. Rheological characterization and modelling of

the rubber to metal vulcanization-bonding process. Polym. Test. 2014, 36, 88-94. (4)

Ansarifar, M. A.; Zhang, J.; Baker, J.; Bell, A.; Ellis, R. J. Bonding properties of rubber to

steel, aluminium and nylon 6, 6. Int. J. Adhes. Adhes. 2001, 21, 369-380. (5)

Souid, A.; Sarda, A.; Deterre, R.; Leroy, E. Influence of reversion on adhesion in the

rubber-to-metal vulcanization-bonding process. Poly. Test. 2015, 41, 157-162. (6)

Sudre, G.; Hourdet, D.; Cousin, F.; Creton, C.; Tran, Y. Structure of surfaces and interfaces

of poly (N, N-dimethylacrylamide) hydrogels. Langmuir 2012, 28, 12282-12287. (7)

Rudawska, A. Selected aspects of the effect of mechanical treatment on surface roughness

and adhesive joint strength of steel sheets. Int. J. Adhes. Adhes. 2014, 50, 235-243. (8)

He, X. A review of finite element analysis of adhesively bonded joints. Int. J. Adhes.

Adhes. 2011, 31, 248-264. (9)

Casado-Dıaz, J.; Fernández-Cara, E.; Simon, J. Why viscous fluids adhere to rugose walls:

A mathematical explanation. J. Differ. Equations. 2003, 189, 526-537.


18

Page 19 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(10) Baldan, A. Adhesion phenomena in bonded joints. Int. J. Adhes. Adhes. 2012, 38, 95-116. (11) Romero-Sánchez, M. D.; Martín-Martínez, J. M. Surface modifications of vulcanized SBR rubber by treatment with atmospheric pressure plasma torch. Int. J. Adhes. Adhes. 2006, 26, 345354. (12) Fombuena, V.; Balart, J.; Boronat, T.; Sánchez-Nácher, L.; Garcia-Sanoguera, D. Improving mechanical performance of thermoplastic adhesion joints by atmospheric plasma. Mater. Design. 2013, 47, 49-56. (13) Treuel, L.; Brandholt, S.; Maffre, P.; Wiegele, S.; Shang, L.; Nienhaus, G. U. Impact of protein modification on the protein corona on nanoparticles and nanoparticle–cell interactions. ACS Nano 2014, 8, 503-513. (14) Picard, L.; Phalip, P.; Fleury, E.; Ganachaud, F. Chemical adhesion of silicone elastomers on primed metal surfaces: A comprehensive survey of open and patent literatures. Prog. Org. Coat. 2015, 80, 120-141. (15) Picard, L.; Phalip, P.; Fleury, E.; Ganachaud, F. Bonding of silicone rubbers on metal:(1) Chemistry of adhesion. Prog. Org. Coat. 2015, 87, 250-257. (16) Raphael, E.; De Gennes, P. G. Rubber-rubber adhesion with connector molecules. J. Phys. Chem. 1992, 96, 4002-4007. (17) Mondal, T.; Bhowmick, A. K.; Krishnamoorti, R. Conducting instant adhesives by grafting of silane polymer onto expanded graphite. ACS Appl. Mater. Inter. 2014, 6, 16097-16105.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 36

(18) Sasaki, H.; Kobayashi, I.; Sai, S.; Hirahara, H.; Oishi, Y.; Mori, K. Adhesion of ABS resin to metals treated with triazine trithiol monosodium aqueous solution. J. Adhes. Sci. Technol. 1999, 13, 523-539. (19) Mori, K.; Hirahara, H.; Oishi, Y. Direct adhesion between electroless nickel-P plated metals and NBR compounds during curing. Rubber. Chem. Technol. 1997, 70, 211-221. (20) Mori, K.; Sasaki, H.; Kobayashi, I.; Sai, S.; Hirahara, H.; Oishi, Y. Adhesion of nylon-6 to triazine trithiol-treated metals during injection molding. J. Adhes. Sci. Technol. 2000, 14, 791803. (21) Hirahara, H.; Aisawa, S.; Mori, K.; Narita, E.; Oishi, Y. Study of interfacial chemistry on direct curing adhesion between Ni-P plating and rubber using 1, 3, 5-triazine-2, 4, 6-trithiol monosodium salt. Surf. Interface. Anal. 2003, 35, 953-959. (22) Xie, Y.; Hill, C. A.; Xiao, Z.; Militz, H.; Mai, C. Silane coupling agents used for natural fiber/polymer composites: A review. Compo. Part A-Appl. S. 2010, 41, 806-819. (23) Lyashenko, I. A.; Pastewka, L.; Persson, B. N. J. Comment on “Friction Between a Viscoelastic Body and a Rigid Surface with Random Self-Affine Roughness”. Phys. Rev. Lett. 2013, 111, 189401. (24) Sang, J.; Hirahara, H.; Mori, K.; Matsuno, Y.; Kudo, T.; Aisawa, S.; Narita, E. Oishi, Y.; Mori, K. Functional group analysis of the surface and cut surface NBR after peroxide cured. Journal of the Society of Rubber Industry, Japan. 2012, 85, 75-80.


20

Page 21 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25) Sang, J.; Aisawa, S.; Hirahara, H.; Mori, K. Primary process to fabricate functional groups on acrylonitrile-butadiene rubber surface during peroxide curing. Chem. Eng. J. 2016, 287, 657664. (26) Ma, P.; Cai, X.; Zhang, Y.; Wang, S.; Dong, W.; Chen, M.; Lemstra, P. J. In-situ compatibilization of poly (lactic acid) and poly (butylene adipate-co-terephthalate) blends by using dicumyl peroxide as a free-radical initiator. Polym. Degrad. Stabil. 2014, 102, 145-151. (27) Mori, K.; Shi, X.; Hirahara, H.; Oishi, Y. Adhesion of rubber to magnesium alloys in the presence of nickel branched alkyl carboxylates. Rubber. Chem. Technol. 2003, 76, 1019-1030. (28) Valentín, J. L.; Rodriguez, A.; MarcosFernández, A.; González, L. Dicumyl peroxide crosslinking of nitrile rubbers with different content in acrylonitrile. J. Appl. Polym. Sci. 2005, 96, 15. (29) Hachisuka, S.; Nakayama, J.; Mori, K.; Hirahara, H.; Oishi, Y. Direct adhesion of natural rubber to nickel/sulfur plating during curing. J. Adhes. Sci. Technol. 2003, 17, 725-736. (30) Sang, J.; Aisawa, S.; Hirahara, H.; Kudo, T.; Mori, K. Heat-resistant organic molecular layer as a joint interface for metal reduction on plastics surfaces. Appl. Surf. Sci. 2016, 368, 4955. (31) Hau, N. Y.; Chang, Y. H.; Feng, S. P. Kinetics study of silver electrocrystallization on (3mercaptopropyl) trimethoxysilane-grafted indium Tin oxide plastic substrate. Electrochimica Acta 2015, 158, 121-128.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 36

(32) Sang, J.; Aisawa, S.; Hirahara, H.; Kudo, T.; Mori, K. Self-reduction and size controlled synthesis of silver nanoparticles on carbon nanosphere by grafting triazine-based molecular layer for conductivity improvement. Appl. Surf. Sci. 2016, 364, 110-116. (33) Frey, S.; Heister, K.; Zharnikov, M.; Grunze, M.; Tamada, K.; Colorado, R.; Graupe, M.; Shmakova, O. E.; Lee, T. R. Structure of self-assembled monolayers of semifluorinated alkanethiols on gold and silver substrates. Israel. J. Chem. 2000, 40, 81-97. (34) Lu, Z. H.; McCaffrey, J. P.; Brar, B.; Wilk, G. D.; Wallace, R. M.; Feldman, L. C.; Tay, S. P. SiO2 film thickness metrology by x-ray photoelectron spectroscopy. Appl. Phys. Lett. 1997, 71, 2764-2766. (35) Fulghum, J. E. Determination of overlayer thickness by angle-resolved XPS: A comparison of algorithms. Surf. Interface. Anal. 1993, 20, 161-173. (36) Opila, R. L.; Eng Jr, J. Thin films and interfaces in microelectronics: composition and chemistry as function of depth. Prog. Surf. Sci. 2002, 69, 125-163. (37) Tiganis, B. E.; Burn, L. S.; Davis, P.; Hill, A. J. Thermal degradation of acrylonitrile– butadiene–styrene (ABS) blends. Polym. Degrad. Stabil. 2002, 76, 425-434. (38) Jiang, H.; Browning, R.; Fincher, J.; Gasbarro, A.; Jones, S.; Sue, H. J. Influence of surface roughness and contact load on friction coefficient and scratch behavior of thermoplastic olefins. Appl. Surf. Sci. 2008, 254, 4494-4499. (39) Zhang, D.; Scarpa, F.; Ma, Y.; Hong, J.; Mahadik, Y. Dynamic mechanical behavior of nickel-based superalloy metal rubber. Mater. Design. 2014, 56, 69-77.


22

Page 23 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(40) Menard, K. P. Dynamic mechanical analysis: a practical introduction. CRC press 2008, P1. (41) Ishida, T.; Choi, N.; Mizutani, W.; Tokumoto, H.; Kojima, I.; Azehara, H.; Hokari, H.; Akiba, U.; Fujihira, M. High-resolution X-ray photoelectron spectra of organosulfur monolayers on Au (111): S (2p) spectral dependence on molecular species. Langmuir 1999, 15, 6799-6806. (42) Petrovykh, D. Y.; Kimura-Suda, H.; Tarlov, M. J.; Whitman, L. J. Quantitative characterization of DNA films by X-ray photoelectron spectroscopy. Langmuir 2004, 20, 429440. (43) Schoenfisch, M. H.; Pemberton, J. E. Air stability of alkanethiol self-assembled monolayers on silver and gold surfaces. J. Am. Chem. Soc. 1998, 120, 4502-4513. (44) Liu, Y.; Li, Y. M.; Li, X. M.; He, T. Kinetics of (3-aminopropyl)triethoxylsilane (APTES) silanization of superparamagnetic iron oxide nanoparticles. Langmuir 2013, 29, 15275-15282. (45) Aradian, A.; Raphael, E.; De Gennes, P. G. A scaling theory of the competition between interdiffusion and cross-linking at polymer interfaces. Macromolecules 2002, 35, 4036-4043. (46) Yu, W.; Peri, S. R.; Akgun, B.; Foster, M. D. Manipulation of polymer/polymer interface width from nonequilibrium deposition. ACS Appl. Mater. Inter. 2013, 5, 2976-2984.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 36

Table of Contents Graphic and Synopsis Figure 1. Schematics of fluid adhesion: (a) adhesive adhesion, (b) curing bonding adhesion, and (c) nonfluid adhesion. Figure 2. Effect of curing temperature on contact angles and on the atomic concentrations of N and O on the cured NBR at different depths from the surface: (a) contact angles, (b) N, (c) O atomic concentration, and (d) COOH functional group concentration. Table 1. Summary of rations of C to N and C to O results and functional groups on NBR surfaces cured at different temperatures. Figure 3. Relationship

between

the friction coefficient and loading

weight

of NBR

surfaces cured at different temperatures. Figure 4. Variation in tan δ with temperature of NBR surfaces cured at 140 °C and 180 °C. Figure 5. (a) Contact angles of NBR surfaces cured at different curing temperatures after TES treatment. XPS spectra of NBR after TES treatment: (b) survey, (c) C1s, and (d) S2p. Figure 6. Influence of curing temperature on the peel strength of NBR/NBR adhesion-joined bodies. Inset photograph of bare NBR/NBR and TES-linked NBR/NBR (cured at 140 °C) adhesion-joined bodies after the peel test; SEM images of the adhesive failure interfaces of TESlinked NBR/NBR (cured at 160 °C, 170 °C, and 180 °C). Figure 7. Schematic of the adhesion mechanism of cured NBR. Figure 8. Transmission electron microphotographs of the TES-linked NBR/NBR adhesion interface.


24

Page 25 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 9. Tan δ vs. temperature curves of NBR and a TES-linked NBR/NBR adhesion-joined body.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 36

Figure 1. Schematics of fluid adhesion: (a) adhesive adhesion, (b) curing bonding adhesion, and (c) nonfluid adhesion.


26

Page 27 of 36

(d)

(a) 2

Depth

COOH Concentration / %

NBR Contact Angle /

˚

100 95

0.7 nm 1.4 nm 1.9 nm 2.3 nm 2.6 nm

1.6

90

1.2

85

0.8

80

70

8

0.4

Surface Cut-surface

75 140

150 160 170 Curing Temp. / ˚C

(b)

0

180

8

140

150 160 170 Curing Temp. / ˚C

(c)

180

Curing Temp.

5 4 3 Curing Temp.

2

140 ˚C 150 ˚C 160 ˚C 170 ˚C 180 ˚C

1

1.0

1.5 2.0 Depth / nm

2.5

O Atomic Concentration / at. %

6

0 0.5

140 150 160 170 180

7

7 N Atomic Concentration / at. %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6

˚C ˚C ˚C ˚C ˚C

5 4 3 2 1

3.0

0 0.5

1.0

1.5 2.0 Depth / nm

2.5

3.0

Figure 2. Effect of curing temperature on contact angles and on the atomic concentrations of N and O on the cured NBR at different depths from the surface: (a) contact angles, (b) N, (c) O atomic concentration, and (d) COOH functional group concentration.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 36

Table 1. Summery of rations of C to N and C to O results and the functional groups on NBR surfaces cured at different temperatures. C1s component / at.% Curing Temp. /℃

140

150

160

170

180

Depth 3λsinθ / nm

N/C Ration /%

O/C Ration /%

*C-C/*CH 284.7 eV

-*CH CH(CN)*CH 285.4 eV

-*CH(CN)/ -*CHOH 286.3 eV

>*CN 286.6 eV

>*CHOH 286.3 eV

>C=O 278.3 eV

-COOH 288.8 eV

0.7

6.3

2.4

74.8

11.4

8.2

5.7

2.5

ー

ー

1.4

6.5

2.2

73.0

12.3

8.6

6.1

2.5

ー

ー

1.9

7.0

2.0

74.4

11.7

8.0

5.9

2.1

ー

ー

2.3

6.8

2.1

71.6

13.2

8.6

6.6

2.0

ー

ー

2.6

7.2

2.0

70.5

13.7

8.9

6.9

2.1

ー

ー

15

6.3

3.1

76.8

10.0

7.7

5.2

2.5

0.3

ー

30

6.9

2.6

73.0

12.3

8.6

6.1

2.5

ー

ー

45

7.3

2.8

71.0

13.3

9.0

6.7

2.4

ー

ー

60

7.2

2.5

70.6

13.6

9.1

6.8

2.3

ー

ー

75

7.3

2.5

69.5

14.1

9.4

7.0

2.4

ー

ー

15

6.3

5.0

75.6

10.2

8.7

5.1

3.6

0.0

0.5

30

7.0

4.0

73.6

11.5

9.0

5.7

3.2

0.0

0.2

45

7.1

3.9

72.0

12.4

9.3

6.2

3.1

0.1

0.1

60

7.2

4.0

71.7

12.5

9.5

6.2

3.3

0.1

0.1

75

7.3

3.5

71.4

12.7

9.5

6.4

3.2

0.0

0

15

2.6

5.1

88.1

4.7

3.5

2.3

1.2

0.1

1.3

30

3.2

4.8

87.4

4.9

3.7

2.4

1.2

0.7

1.0

45

4.4

4.3

85.8

5.8

4.9

2.9

2.0

0.2

0.5

60

5.3

3.9

84.5

6.7

5.5

3.2

2.3

0.0

0.1

75

5.5

3.3

83.4

7.3

5.7

3.5

2.2

0.0

0.1

15

6.3

2.4

87.7

4.4

3.3

2.1

1.2

0.7

1.7

30

6.5

2.2

85.6

5.6

4.6

2.6

2.0

0.2

1.4

45

7.0

2.0

84.4

6.1

5.2

3.1

2.2

0.2

1.0

60

6.8

2.1

82.7

7.1

6.0

3.6

2.5

0.1

0.6

75

7.2

2.0

82.8

7.0

6.0

3.5

2.5

0.3

0.3

2

2


28

Page 29 of 36

3.0 140 150 160 170 180

2.5

Friction Coefficient

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


℃ ℃ ℃ ℃ ℃

2.0

1.5

1.0

0

10

20

30

40

50

Load / g

Figure 3. Relationship

between

the friction coefficient and loading

weight

of NBR

surfaces cured at different temperatures.


29


0.05 Curing Temp. 0.04

140 ˚C 180 ˚C

0.03 Tan δ

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 36

0.02 0.01 0 -120 -100 -80 -60 -40 -20 0 Temp. / ˚C

20

40

60

80

Figure 4. Variation in tan δ with temperature of NBR surfaces cured at 140 °C and 180 °C.


30

Page 31 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a) Contact angles of NBR surfaces cured at different curing temperatures after TES treatment. XPS spectra of NBR after TES treatment: (b) survey, (c) C1s, and (d) S2p.


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 36

Figure 6. Influence of curing temperature on the peel strength of NBR/NBR adhesion-joined bodies. Inset photograph of bare NBR/NBR and TES-linked NBR/NBR (cured at 140 °C) adhesion-joined bodies after the peel test; SEM images of the adhesive failure interfaces of TESlinked NBR/NBR (cured at 160 °C, 170 °C, and 180 °C).


32

Page 33 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


HS

N

HS N

N

OH OH

N

SH

N

N

N

+

H2C CH2 H5C2O Si

OC 2H 5

O Si O

O Si O

O

O

Cured NBR

OC2H 5

Cured NBR

O

O

O

O Si O

O Si O

N

N

O Si

NH CH 2

Cured NBR

SH HS

N

N

OH

Cured NBR

Cured NBR

SH

TES treatment

pressure heat

N

H2O

N

HS

N

SHHS

N

SH

HS

N

SHHS

N

SH

N

N

N

N

O Si O

O Si O

O

O

N

O O

O

N

Si O

N

N

S

N

S

S

N

S

S

N

S

S

N

S

N O

Si O

N

N

O

O

Chemical bond

N Si

O

O

Cured NBR

Cured Cured NBR

Adhesion process

NBR/NBR jointed body

Figure 7. Schematic of the adhesion mechanism of cured NBR.


33


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 36

TES molecular adhesive layer

Figure 8. Transmission electron microphotographs of the TES-linked NBR/NBR adhesion interface.


34

Page 35 of 36

0.06

NBR NBR/NBR adhesion

0.05 0.04 Tan δ

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.03 0.02 0.01 -120 -100 -80

-60

-40

-20

0

20

40

60

80

Temp. / ˚C

Figure 9. Tan δ vs. temperature curves of NBR and a TES-linked NBR/NBR adhesion-joined body.


35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 36

TOC Graphic


36

Rubber Through Covalent

Recommend Documents