Low Interfacial Adhesion Research Articles

Combined Dependence of Nanoconfined Tg on Interfacial Energy and Softness of Confinement.

We employ molecular dynamics simulations of nanolayered polymers to systematically quantify the dependence of Tg nanoconfinement effects on interfacial energy and the "softness" of confinement. Results indicate that nanoconfined Tg depends linearly on interfacial adhesion energy, with a slope that scales exponentially with the ratio of the bulk Debye-Waller factors ⟨u2⟩ of the confined and confining materials. These trends, together with a convergence at low interfacial adhesion energy to the Tg of an equivalent freestanding film, are captured in a single functional form, with only three parameters explicitly referring to the confined state. The observed dependence on ⟨u2⟩ indicates that softness of nanoconfinement should be defined in terms of the relative high frequency shear moduli, rather than low frequency moduli or relaxation times, of the confined and confining materials.

Fracture Micromechanisms of Polypropylene/Polycarbonate/Poly(styrene-b-(ethylene-co-butylene)-b-styrene) (PP/ PC/SEBS) Ternary Blends: The Effects of SEBS Content

Ternary blends of polypropylene/polycarbonate/poly(styrene-b-(ethylene-co-butylene)-b-styrene) (PP/PC/SEBS) with varying SEBS contents were produced via melt blending in a co-rotating twin-screw extruder. The phase morphology of the resulting ternary blends and its relationship with bending and impact behaviors were studied. Transmission optical microscopy (TOM) of the crack tip damage zone and scanning electron microscopy (SEM) of impact fractured surfaces were performed to characterize the fracture mechanism. With increasing SEBS content in the PP/PC/SEBS ternary blends, the number of PC/SEBS core-shell particles increased and the size of the core-shell particles enlarged. It was shown that with an SEBS content of 5%, the crack initiation resistance decreased and then was almost unchanged with further increase of SEBS content, while resistance to crack growth increased continuously with increasing of SEBS content. Preliminary analysis of the micromechanical deformation suggested that the high impact toughness observed for samples containing 20 and 30 wt% of SEBS could be attributed to cavitation of the rubbery shell and, consequently, shear yielding of the matrix. This plastic deformation absorbed a tremendous amount of energy. Due to low interfacial adhesion between PC particles and PP matrix in samples containing 5 and 10 wt% of SEBS, debonding occurred too early, so the occurrence of matrix shear yielding was delayed and resulted in premature interfacial failure and, hence, rapid crack propagation.

Influence of the degree of crosslinking on the stringiness of crosslinked polyacrylic pressure‐sensitive adhesives

ABSTRACTThe stringiness of crosslinked polyacrylic pressure‐sensitive adhesive (PSA) was observed during 90° peeling under the constant peel load. The random copolymer of butyl acrylate with 5 wt % acrylic acid crosslinked by N,N,N′,N′‐tetraglycidyl‐m‐xylenediamine was used as PSA. All observed stringiness upon peeling was sawtooth‐shaped, but it could be classified into three types dependent on the degree of crosslinking. The typical sawtooth‐shaped stringiness with interfacial failure was observed at the relatively higher crosslinker content ranging from 0.008 to 0.016 chemical equivalents (Eq.), where the PSA has high cohesive strength and low interfacial adhesion. The frame formed at the front end of stringiness at the content ranging from 0.002 to 0.004 Eq. Sufficient interfacial adhesion and deformability generate large internal deformation of the PSA layer. Internal deformation occurred preferentially over peeling as a result of front frame formation. The mode of peeling was changed from cohesive failure to interfacial failure in this range of crosslinker content. The sawtooth‐shaped with cohesive failure was observed at the lower content ranging from 0 to 0.001 Eq. The PSA has high interfacial adhesion and low cohesive strength, and thus exhibited cohesive failure. The PSA after peeling remained in the shape of belts. It was found that the shape of stringiness is strongly dependent on the balance between the interfacial adhesion and the cohesive strength of PSA. When the sawtooth‐shaped stringiness with frame formed, the peeling rate was lowest. This means the peel strength should be the maximum in this shape of stringiness. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40336.

Mejoramiento de las Propiedades de Tensión en WPC de LDPE: HIPS/Fibra Natural Mediante Entrecruzamiento con DCP

Straight Retamo Fiber (telinemonspessulana) was mixed in a polymer matrix formed by low density polyethylene (LDPE) and high impact polystyrene (HIPS) in a 70:30 ratio. The natural fiber was subjected to size reduction between 1700 and 850 µm; surface treatment mercerization was performed; the moisture content was 0.17%. The thermo gravimetric analysis (TGA) showed that the treated fiber has stability at 200.53 °C. The preparation of the compound was performed in an internal mixer with the samples being obtained by compression molding. The effect of crosslinking agent was evaluated: dicumyl peroxide (DCP) in compounds with various percentages of fiber: 0; 10; 25; 50 phr. The addition of DCP (1 phr) in the compounds significantly improved tensile properties compared to similar concentrations of fiber; however, this difference in property values progressively decreased when the amount of fiber approximated 50 phr. The increase in fiber concentration negatively affected the tensile properties, except for the modulus of elasticity and fluence resistance. The main cause is the low interfacial adhesion between the natural fiber and the polymer matrix, clearly evidenced in the SEM images.

Effect of Rare Earth Cerium on the Synthesis and Wear-Resistance of Electroless Ni-P-PTFE Coatings

By adding various concentrations of rare earth cerium into the acidic hypophosphite plating baths, electroless Ni-P-PTFE coatings have been successfully deposited on the surface of shaft made of mild steel. Surface morphology, microhardness and interfacial adhesion of the coatings were characterized by scanning electron microscope equipped with energy dispersive spectrometer, vicker microhardness meter and WS-92 scrape instrument, respectively. Ring-plate wear test was applied to study the friction coefficient and wear resistance of Ni-P-PTFE coating. Results revealed that Ni-P-PTFE coatings deposited with 10ppm or 20ppm cerium in the plating baths show low friction coefficient and high interfacial adhesion,leading to its perfect wear resistance. However, both the interfacial adhesion and wear resistance of the Ni-P-PTFE coatings were decreased drastically as the cerium concentration in the plating baths was exceeds 50ppm.

폴리카보네이트 필름 표면 처리가 증착 SiOx베리어층 접착에 미치는 영향

폴리카보네이트(PC) 필름을 유연기판으로 사용하기 위해서는 <TEX>$SiO_x$</TEX> 증착에 의한 베리어 특성 개선이 필요하며 이때 베리어 층과 PC 계면 접착력이 매우 중요하다. 본 연구에서는 언더 코팅, UV/<TEX>$O_3$</TEX> 및 저온 플라즈마와 같은 다양한 표면 처리 방법에 의하여 PC 필름 표면을 개질하여 표면의 물리적 화학적 변화가 증착된 베리어 층 계면 접착력에 미치는 영향을 살펴보았다. 표면 처리 전의 PC 필름은 표면 거칠기 및 표면 에너지가 매우 낮아 <TEX>$SiO_x$</TEX> 베리어 층과의 접착력이 현저히 떨어짐을 알 수 있었다. PC 필름을 저온 플라즈마로 표면 처리한 결과, 표면의 거칠기 증가와 극성 관능기 생성에 의하여 극성 표면 에너지가 향상되는 반면 UV/<TEX>$O_3$</TEX> 처리의 경우, 표면 거칠기 변화 없이 표면에 생성된 극성 관능기에 의해 극성 표면 에너지가 증가됨을 알 수 있었다. 이러한 표면의 변화는 베리어층과 PC 기판의 계면 접착력 증가에 기여함을 알 수 있었다. 표면 처리 방법으로 언더 코팅을 사용하는 경우 표면에 에너지를 가하지 않아도 코팅제의 아크릴산과 <TEX>$SiO_x$</TEX>의 접착력 향상에 의하여 PC 필름과의 계면 접착력이 증가되며 유무기 하이브리드 다층 구조에 의한 베리어 특성 개선이 함께 일어남을 알 수 있었다. The interfacial adhesion strength is very important in <TEX>$SiO_x$</TEX> deposited PC film for the barrier enhanced polycarbonate (PC) flexible substrate. In this study, PC films were treated by undercoating, UV/<TEX>$O_3$</TEX> and low temperature plasma and then the effect of physical and chemical surface modifications on the interfacial adhesion strength between PC film and <TEX>$SiO_x$</TEX> barrier layer were studied. It was found that untreated PC film shows significantly low interfacial adhesion strength due to the smooth surface and low surface free energy of PC. Low temperature plasma treatments resulted in the increase of both surface roughness and surface free energy due to etching and the appearance of polar molecules on the PC surface. However, UV/<TEX>$O_3$</TEX> treatment only shows the increase of surface free energy by developed polar molecules on the surface. These surface modifications caused the enhancement of surface interfacial strength between PC film and <TEX>$SiO_x$</TEX> barrier. In the case of undercoating, it was found that the increase of surface interfacial strength was achieved by adhesion between various acrylic acid on acrylate coated surface and <TEX>$SiO_x$</TEX> without increase of polar surface energy. In addition, the barrier property is also improved by organic-inorganic hybrid multilayer structure.

Fully biodegradable potato starch composites: effect of macro and nano fiber reinforcement on mechanical, thermal and water-sorption characteristics

Nature provides an impressive array of polymers which are generally biodegradable, as biodegradation is part of the natural biogeochemical cycle. Natural polymers, such as starch and cellulose have the potential to replace many current polymers if new material composites can be prepared to rival the performance of exisitng composites. While the conventional composites offer excllent mechanical properties and durability, most commercial polymers are derived from petroleum feed stock. Even though the utilization of petroleum-based composites are non-biodegradable and environmentally undesirable. Environment-friendly “Green” composites, based on potato starch and reinforced with nanocellulose/ramie fabric were prepared by hot compression moulding technique. PCL was coated to reduce water sensitivity. In the absence of reinforcing fillers, residual thermal stress transfer is affected. For reinforced composites, mechanical properties were seen to increase as a result of reinforcement. In composites containing the hydrophilic nanofibres and the hydrophobic PCL, phase inhomogeneity causes lower mechanical properties. Elongation at break increased for multiphase composites due to low interfacial adhesion. The uniform web-like network of nanofibres decreases water sorption. However, the presence of hydrophilic lignocellulosics increases water sorption. The PCL- containing composites show a low water sensitivity as expected. The nanostructure of the composites were analysed using TEM studies. A detailed investigation on the thermal properties of the thermoplastic potato starch were done by thermogravimetric analysis and flammability studies were done by limiting oxygen index analysis. The starch polymer is almost stable up to 300 °C. Also they showed better flame retardant properties.

Flammability and mechanical properties of Al(OH)3 and BaSO4 filled polypropylene

The flammability and mechanical properties of Al(OH)3/BaSO4/polypropylene (PP) composites were investigated. The flow, morphological, and thermal properties were also analyzed by melt flow index (MFI), Scanning electron microscopy (SEM), and Differential scanning calorimeter (DSC) studies, respectively. Total filler amount was fixed at 30 wt % to optimize physical characteristics of the composites. In addition to the flame retardant filler Al(OH)3, BaSO4 was used to balance the reduction in impact strength at high filler loadings. Substantial improvement in mechanical properties was achieved for 20 wt % Al(OH)3 (i.e., 10 wt % BaSO4) composition while maximum flammability resistance was obtained for 30 wt % Al(OH)3 composite. SEM studies showed that the presence of aggregated Al(OH)3 particles led to low interfacial adhesion between them and PP matrix ending up with decreased mechanical strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Possible use of ultra-fine acrylonitrile butadiene rubber powder as filler in natural rubber vulcanizates

Possible use of ultra-fine acrylonitrile butadiene rubber powder (UFNBRP) as a filler for natural rubber (NR) was investigated. The UFNBRP was added into NR at various concentrations, and the compound properties were determined. It is found that, with increasing UFNBRP loading, the compound viscosity is increased, whereas both scorch time and optimum curing time are significantly reduced. The results also reveal that UFNBRP has negative effect not only on crosslink density but also on most mechanical properties of the vulcanizate, such as tensile strength, tear strength, compression set, and abrasion resistance. The deterioration of these mechanical properties is thought to arise mainly from the combined effect of large phase size of the dispersed UFNBRP and low interfacial adhesion taking place from the polarity difference between UFNBRP and NR. Interestingly, it is found that, after aging, UFNBRP could promote postcuring phenomenon leading to increases of both relative 100% modulus and relative tensile strength. Oil resistance is also found to improve considerably with increasing UFNBRP loading. This improvement is mainly attributed to the dilution effect, i.e., the higher the UFNBRP loading, the lower the NR portion and, thus, the greater the oil resistance of the vulcanizate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Development of acyl-bonded aminopropyl silica gel fillers with low interfacial adhesion energy in a polystyrene matrix

To develop fillers that adhere closely to a matrix polymer and reduce the glass transition temperature (Tg) of filler/polymer composites, N-acyl-3-aminopropyl silica gel fillers (1) were prepared by the reaction of 3-aminopropyl silica gel (SiO2–NH2) and succinimidyl alkanoate (2) by controlling the amount and length of alkyl chains. The surface tension (γ) of 1 was measured by the wicking method. The interfacial adhesion energy (W) of composites (1/PS) between 1 and polystyrene (PS) was calculated using the dispersive component (γD) and the polar component (γP) of γ, according to the Equation ( ) where subscripts m and f indicate matrix and filler, respectively. The W values of 1/PS composites were considerably smaller than those of the SiO2–NH2/PS composite. A good correlation between W and Tg showed that the introduction of acyl groups on SiO2 was effective for the enhancement of adhesion between 1 and the matrix polymer. Moreover, it was confirmed that the addition of less than 30 wt% of 1 to PS did not affect the tensile strength of composites. N-Acyl-3-aminopropyl silica gel fillers (1) are developed to reduce the interfacial adhesion energy (W) between fillers and polystyrene (PS). The effects of alkyl chains on the W interface force have been evaluated by surface tension of 1 and PS. Moreover, the adhesion of 1 toward PS was evaluated by glass transition temperature measured by DSC.

Effect of a Novel Coupling Agent, Polybutadiene Isocyanate, on Mechanical Properties of Wood-Fiber Polypropylene Composites

The scope of the present paper is to study the effect of adding a novel coupling agent, polybutadiene isocyanate (PBNCO), on the mechanical properties of hardwood aspen fiber/polypropylene (PP) composites. The resulting properties were compared to those obtained with the most commonly used coupling agent, maleic anhydride modified polypropylene (MAPP). In this study, we determined a value of 24.75 MPa for the tensile strength of pure PP and 22 MPa for the composite containing 30 or 40wt% unmodified fibers. These results indicate that wood fiber behaves merely as filler when incorporated into PP and no reinforcing effect was observed in this case. This occurs because of the chemical incompatibility between the thermoplastic PP and the polar fiber, resulting in low interfacial adhesion. However, it was verified that addition of 3% MAPP and 5% PBNCO to this formulation produced composites with better performance, since the tensile and impact properties were increased up to 30 MPa and 22 J/m2, respectively. This behavior can be attributed to the enhanced interfacial bond between reinforcing fibers and polymer matrix modified MAPP and PBNCO treatments, play a significant role in improving the mechanical properties of the composites. The increase in mechanical properties demonstrated that PBNCO is an effective coupling agent for wood fiber/PP composites.

Structure–property relationships in nanocomposites

A numerical finite-difference model is presented for the study of the factors controlling the properties of composites reinforced with platelets and fiber-like nano-inclusions. The approach provides a comprehensive treatment of the dependence of composite modulus and strength on the shape of the inclusions and the interrelated effects of their orientation, volume fraction, aspect ratio, modulus and interfacial properties with the matrix. At the same volume fraction, we find that platelets are generally more efficient than fibers in improving composite modulus. This is rationalized through our model finding that fibers have a typically low critical aspect ratio value, which puts an upper limit to their reinforcement potential. Platelets also turn out to be superior to fibers in all nanocomposites characterized by a poor orientation of the inclusions. We also find that low interfacial adhesion and poor dispersion of the inclusions lead to a decrease in reinforcement efficiency. Turning to comparison with experiment, a good agreement is found between our model predictions and modulus data on nanocomposites reinforced with montmorillonite platelets and carbon nanotubes.

Performance characterization of composite materials based on recycled high‐density polyethylene and ground tire rubber reinforced with short glass fibers for structural applications

AbstractThis study addresses the issue of using recycled materials to obtain low‐cost structural products for practical applications. Through the use and re‐extrusion of virgin high‐density polyethylene (HDPE), the effects of the degradation level of HDPE as a matrix phase on its mechanical properties and the mechanical performance of composites produced with the degraded polyethylene have been examined. The degradation level of HDPE caused by re‐extrusion has been evaluated by the measurement of the melt flow index and mechanical properties of virgin and degraded HDPEs. The results indicate that the modulus and strength of HDPE significantly increase with the addition of polypropylene filled with 30 wt % glass fiber [PP–GF(30)] without any other compatibilizer. However, the final properties of composites with specified glass‐fiber contents are dependent on the degradation level of the matrix phase. In addition, the role of ground tire rubber (GTR) in HDPE/PP–GF(30) systems has been examined by the preparation of composites with various GTR contents without any treatments. The results show that the presence of GTR in the final product results in lower stiffness because of its role as a soft filler, but the elongation of the product increases slightly. Furthermore, GTR does not produce any improvement in the impact properties, probably because of the low interfacial adhesion with the matrix phase; therefore, its content should be kept low in the final composition. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effect of Interfacial Adhesion on the Mechanical Properties of Organic/Inorganic Hybrid Nanolaminates

Two different kinds of organic polyelectrolyte (PE)/inorganic silicate nanolaminates carrying dissimilar interfacial adhesion between the organic and the inorganic layers were prepared using the layer-by-layer self-assembly. To investigate the mechanical behavior of the prepared hybrid films, apparent modulus (E′), hardness (H), and crack length were measured by depth-sensing nanoindentation as well as a microVickers experiment. The fracture toughness of the hybrid films was then calculated based on the measured mechanical values. In the case of forming strong interfacial adhesion between the organic and the inorganic layers (A series), the fracture toughness and the crack resistance of hybrid multilayer films were significantly improved as a result of the redistribution of stress concentration and the dissipation of fracture energy by the plasticity of organic PE layers. On the other hand, samples with relatively low interfacial adhesion between the organic and the inorganic layers (T series) had little effect on the improvement of fracture toughness of the hybrid films.

Mechanical analysis for crack-free release of chemical-vapor-deposited diamond wafers

Chemical-vapor-deposited (CVD) diamond thick films for electronic applications must be released without cracks from the substrate as freestanding wafers. In this study, the mechanism of cracking in the CVD films was investigated experimentally and theoretically. Experimental observations showed that cracks initiated at the edge of the diamond wafer and then propagated towards the center. Finite-element analysis (FEA) reveals that, during cooling, compressive thermal stresses concentrate at the thick film's edge and additional tensile stress acts circumferentially. This was verified by the experimental analysis of diamond films deposited on Si, Mo and W substrates. Observations on low interfacial adhesion and crack-free film on the W substrate indicated that, in addition to the high thermal stress, low interfacial adhesion plays an important role in cracking. Thus, film cracking depends on the fracture strength of the film and its relative magnitude with respect to interfacial adhesion. Methods of crack suppression were suggested on the basis of this cracking mechanism: increase of film thickness and minimization of the substrate's CTE and interfacial adhesion. The analysis was confirmed by successful suppression of cracking by application of a low-adhesion interlayer prior to deposition of diamond film.

Morphology-interface-toughness relationship in polyamide/polysulfone blends by reactive processing

By reactive blending of polyamide 6 (PA) with polysulfone (PSU) using a gram-scale mixer (Mini–Max Molder), we prepared a series of PA/PSU (80/20wt. ratio) blends with various diameters of PSU particles; 70nm by using phthalic anhydride-terminated PSU (PSU-PhAH), 0.4μm by epoxy-terminated PSU, 0.45μm by maleic anhydride-grafted PSU and 1.3μm by non-reactive PSU. By light scattering (LS), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry, it was shown that there did not exist any difference in the crystalline morphology of PA matrix among the blends. Although difference in tensile strength among blends was small but on elongation it was large; the smaller PSU particles yielded larger elongation at break. The bulk-fracture toughness was shown to be higher for the blend with smaller PSU particles. Especially, PSU-PhAH blend showed a remarkably high toughness. In this blend, ductile fracture was shown by SEM observation. Transmission electron microscopic (TEM) observation confirmed the homogenous plastic deformation without interfacial debonding in the two-phase material. In contrast, other blends showed brittle fracture accompanied with interfacial debonding. The adhesive strength between PA and PSU-PhAH phases measured by asymmetric double cantilever beam method was shown to be much higher than in other systems. Thus, when the interfacial adhesive strength is high enough to provide adequate stress transfer, plastic deformation of brittle PSU particle can occur and hence the uniform plastic deformation of the whole material may render high toughness. The lower interfacial adhesion seems to yield in less massive plastic deformation to resulting in lower toughness.

Characterization of thermotropic liquid crystalline polyester/polysulfone blends

AbstractThe morphology, rheology, and mechanical properties of blends of polysulfone (PSF) with up to 65% of a wholly aromatic liquid crystalline polymer (LCP) were investigated. In injection molded specimens a skin‐core morphology was observed with the LCP minor phase oriented in the skin and globular in the core. Scanning electron microscopy of fractured surfaces showed sharp phase boundaries, suggesting low interfacial adhesion. The neat PSF and blends with low amounts of LCP exhibited a low shear Newtonian plateau not observed in the blends with high LCP levels. The addition of LCP to PSF resulted in an increase in stiffness, a small increase in tensile strength, and a significant improvement in processability.