Study on the toughening mechanism of PP/EVA dynamically crosslinked blend

The toughening mechanism of polypropylene (PP)/ethylene-co-vinyl acetate (EVA) dynamically crosslinked blend was investigated. The results indicated that dynamical crosslinking technology not only improved the interfacial adhesion between PP and EVA, but also increased the mechanical properties of PP/EVA blend. The quantitative and qualitative analysis of scanning electron microscopy (SEM) micrographs demonstrated that dynamical crosslinking technology could refine EVA particles in PP/EVA blend and promote the size distribution of EVA particles. The critical matrix ligament thickness of dynamically crosslinked and uncrosslinked blend was about 0.55 μm and 0.6 μm, respectively, indicating that the brittle-ductile transition occurred. Dynamic mechanical analysis (DMA) results illustrated that the tan δ peak of PP component in the dynamically crosslinked blend moved toward lower temperature compared with that of pure PP and the PP component in uncrosslinked blend; and the tan δ value of the dynamically crosslinked blend was higher than that of the uncrosslinked blend, which interpreted the toughening mechanism of dynamical crosslinking technology from the dynamic mechanical property of the blend.     

Effect of silane coupling agent on mechanical interfacial properties of glass fiber‐reinforced unsaturated polyester composites

A silane coupling agent, γ‐methacryloxypropyltrimethoxysilane, for the surface modification of glass fibers was varied between 0.1 and 0.8 wt %. To understand the role of interfacial adhesion of glass fiber/unsaturated polyester composites, contact angles of the silane‐treated glass fibers were measured by the wicking method on the basis of the modified Washburn equation with deionized water, diiodomethane, and ethylene glycol as testing liquids. As a result, silane‐treated glass fibers led to increased surface free energy, mainly because of their increased specific or polar component. The mechanical interfacial behaviors based on the interlaminar shear strength (ILSS) of the composites determined by short‐beam tests and the critical stress‐intensity factor (K_IC) were also improved in the case of silane‐treated composites. The surface free energy and the mechanical interfacial properties especially showed the maximum value in the presence of 0.4 wt % silane coupling agent. It revealed that the increase of a specific component of the surface free energy or hydrogen bonding between the glass fibers and the coupling agents plays an important role in improving the degree of adhesion at interfaces in a composite system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 55–62, 2003     

The synergetic effect of zinc phthalate and carboxymethyl cellulose–carbon nanotube of glass fibers surfaces on improving strength and toughness of polypropylene composite

The interfacial interaction between glass fibers (GFs) and polypropylene (PP) resin is the key factor which affects the properties of GFs reinforced PP composites. The β-transcrystallization (β-TC) structure induced by β-nucleating agent (β-NA) at the interface is beneficial to improving the interfacial performance and comprehensive mechanical properties. However, due to the poor adhesive ability, it is difficult to introduce β-NAs onto GFs surface directly. In this work, for solving above problem, the sodium carboxymethyl cellulose (CMC) and  NH₂ functionalized multiwalled carbon nanotubes (CNTs) were used to construct the network structure on GFs (CMC-CNT-GF) through plenty of active groups. Furthermore, the zinc phthalate (ZnPht, β-NA) was synthesized and coated on GFs surface by hydrogen bonds interaction with CMC-CNT and physical anchoring effect (ZnPht@CMC-CNT-GF). Finally, the hybrid GFs reinforced PP composite (iPP/ZnPht@CMC-CNT-GF) was prepared, which exhibited enhanced tensile, flexural, and impact strength by 20.1, 9.3, and 33.3%, respectively when compared with the iPP/raw GF due to the formation of β-TC and improvement of interfacial adhesion. This study provides an effective strategy to introduce β-NAs on GFs with network structure for improving interfacial properties by inducing β-TC to enhance the strength and toughness of composite, which could be applied in other fiber/semicrystalline polymer systems.     

Preparation and properties of water‐absorbent composites of chloroprene rubber,starch, and sodium acrylate

The effects of the amounts of starch, sodium acrylate (NaAA) and dicumyl peroxide (DCP) on the properties of chloroprene rubber (CR)/starch/NaAA composites prepared by melting method were investigated. The results showed that the addition of starch improved the mechanical properties, but decreased the water‐absorbing capacity of the composite, most likely due to the decrease in the local concentration of the main water‐absorbing material sodium polyacrylate and the increase in crosslinking density of the composite resulting from the reaction between starch and CR. This reaction was verified by the vulcanized curves, DSC curves, and the cut surface morphology. The as‐prepared composite demonstrated higher water‐absorbing capacity, resulting from the incorporation of NaAA. The mechanical properties decreased with increasing the DCP loading, and the water‐absorbing ratio is the maximum at 1.0 phr DCP. The tensile strength of the composite decreased significantly after water immersion, due to the absorbed water acting as a plasticizer. The extracted component from composites after water immersion is mainly sodium polyacrylate according to Fourier transform infrared (FT‐IR) spectroscopy analysis. The morphology of the composites before and after water immersion was observed by optical transmission microscopy (OTM). The results indicated that the starch exhibits a good dispersion state, and the water‐absorbing capacity results primarily from sodium polyacrylate. Copyright © 2010 John Wiley & Sons, Ltd.     

Monocomponent Waterborne Polyurethane Adhesives: Influence of the Crosslinking Agent on Their Properties

To improve the properties of the monocomponent waterborne polyurethane (WPU) adhesives, a series of crosslinked WPU were prepared with trifunctional polyester polyol (P210) as crosslinking agent. The crosslinked WPU dispersions and their films were characterized by conventional methods. The adhesion property of the samples was measured from T-peel test of leather/WPU adhesive/leather joints. Compared with the linear one, the crosslinked WPU exhibited low viscosity, small particle size, and low surface tension. For crosslinked films, the thermal stability, water resistance and mechanical properties were remarkably enhanced. The experimental data of T-peel test indicated that the adhesive strength significantly increased to 4.8 KN/m by crosslinking up to the optimum crosslink index of 1.2 and then showed a small decrease with excess.     

Effect of long fiber thermoplastic extrusion process on fiber dispersion and mechanical properties of viscose fiber/polypropylene composites

Viscose fiber reinforced polypropylene (PP/VF) composites were manufactured using long fiber thermoplastic (LFT) extrusion techniques with two different methods namely LFT‐l and LFT‐2. The compatibilizer [maleated polypropylene (MAPP)] and dispersing agent [stearic acid (SA)] were added to the PP/VF in order to improve the fiber dispersion and interfacial adhesion. The PP/VF composites manufactured using LFT‐2 showed better fiber dispersion with higher tensile and flexural properties compared to the composites manufactured using LFT‐1 method. Similarly, the impact strength and toughness of the LET‐2 composites showed an improvement of 36 and 20% than LFT‐1 whereas the average fiber length of composites was decreased from 6.9 mm to 4.4 mm because of the increase in shear energy as a result of residence time. Further, the addition of SA and MAPP to LFT‐2 process has significantly improved the fiber dispersion and mechanical performance. The fiber dispersion and fracture behavior of the LFT‐1 and LFT‐2 composites were studied using scanning electron microscopy analysis. The Fourier transformation infrared spectra were also studied to ascertain the existence of type of interfacial bonds. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of trimethylsilyl substituents in the monomer unit on the energy characteristics of surfaces of polynorbornenes obtained via metathesis polymerization

The surface properties of polynorbornenes obtained via metathesis polymerization are investigated via the wetting method. The incorporation of trimethylsilyl groups into the monomer unit causes decreases in the specific free surface energies of the investigated polymers. It is found that the dispersion terms of the specific free surface energies correlate with the free-volume and gas-permeability values of the polymers. As shown through the methods of differential scanning calorimetry and FTIR spectroscopy, during heating in air, the considered polynorbornenes undergo oxidative crosslinking, which increases their specific free surface energies. The interphase energies of crosslinked polynorbornenes are determined at their interfaces with liquids modeling polar and nonpolar phases, and the values of the work of adhesion of the crosslinked polynorbornenes to the model liquids are calculated. It is shown that the work of adhesion of the polymer to the polar phase decreases after introduction of trimethylsilyl groups, while the combination of polar and nonpolar phases give rise to an increase in the work of adhesion.     

Adsorption of Triton X-100 and cetyltrimethylammonium bromide mixture with ethanol at nylon-6–solution interface with regard to nylon-6 wettability: II. Work of adhesion and activity of surfactants at interfaces

On the basis of the values of the surface tension of the aqueous solutions of the Triton X-100 and CTAB mixture with ethanol, the surface tension of nylon-6 and the nylon-6–solution interfacial tension, the activity of the surfactant mixture and ethanol at the nylon-6–solution interface was calculated and compared to that at the solution–air one. For these calculations, the Sprow and Prausnitz equation was applied. The obtained values of the activity were used for the calculations of the work of adhesion of the solution to the polymer surface. The values of the work of adhesion obtained in this way were compared to those determined from the Young–Dupre equation by using the contact angle values of the aqueous solutions of the TX-100 and CTAB mixture with ethanol measured on the nylon-6 surface. The changes of the work of adhesion determined from the Young–Dupre equation were also considered as a function of the surface tension of the solution, its polar component and the interfacial interaction parameter.     

Chemical force spectroscopy in heterogeneous systems: intermolecular interactions involving epoxy polymer,mixed monolayers,and polar solvents

We used chemical force microscopy (CFM) to study adhesive forces between surfaces of epoxy resin and self-assembled monolayers (SAMs) capable of hydrogen bonding to different extents. The influence of the liquid medium in which the experiments were carried out was also examined systematically. The molecular character of the tip, polymer, and liquid all influenced the adhesion. Complementary macroscopic contact angle measurements were used to assist in the quantitative interpretation of the CFM data. A direct correlation between surface free energy and adhesion forces was observed in mixed alcohol-water solvents. An increase in surface energy from 2 to 50 mJ/m(2) resulted in an increase in adhesion from 4-8 nN to 150-300 nN for tips with radii of 50-150 nm. The interfacial surface energy for identical nonpolar surface groups of SAMs was found not to exceed 2 mJ/m(2). An analysis of adhesion data suggests that the solvent was fully excluded from the zone of contact between functional groups on the tip and sample. With a nonpolar SAM, the force of adhesion increased monotonically in mixed solvents of higher water content; whereas, with a polar SAM (one having a hydrogen bonding component), higher water content led to decreased adhesion. The intermolecular force components theory was used for the interpretation of adhesion force measurements in polar solvents. Competition between hydrogen bonding within the solvent and hydrogen bonding of surface groups and the solvent was shown to provide the main contribution to adhesion forces. We demonstrate how the trends in the magnitude of the adhesion forces for chemically heterogeneous systems (solvents and surfaces) measured with CFM can be quantitatively rationalized using the surface tension components approach. For epoxy polymer, inelastic deformations also contributed heavily to measured adhesion forces.     

Novel Tailored Polymeric Surfactant for Dispersing Clay into the Non Polar Polymer

Polymers have entropy nearly zero which cause mixing of different polymers or with the fillers become very difficult. There is generally a third component necessary which is called surfactant to enhance the miscibility. The surfactant reduces interfacial tension and improves the interfacial adhesion. In this work, tailored polymeric surfactant is designed and utilized for dispersing the clay in nano scale in to the polymer matrix Polypropylene (PP). These were prepared directly from Na⁺ Bentonite by reactive processing in which melt intercalation technique was carried. They are Polypropylene-g-acrylic amido Poly(oxypropylene) ammonium chloride (POPA). This ammonium salt was prepared from diamine and Polypropylene-g-acrylic acid by the formation of amido amine and sequentially neutralized it with the hydrochloric acid solution. The amido amine formation was verified by the FTIR technique. Clay loading was kept at 5 weight % by this new technique. Their structures were characterized by x-ray diffraction (XRD). The distribution of clay in the matrix was also studied through optical microscope (OM) and scanning electron microscope (SEM). These techniques revealed that the polymeric surfactant enhances the dispersion and the dispersed clay is hardly found in the SEM images.     

Chemical force microscopy study of adhesive properties of polypropylene films: influence of surface polarity and medium

The adhesive properties of untreated and corona treated polypropylene (PP) films were studied in polar (water) and nonpolar (hexadecane) liquid medium by using chemical force microscopy. A gold-coated colloidal probe was sequentially modified with self-assembled monolayers (SAMs) of omega-functionalized alkanethiols. The same colloidal probe was used for the force measurements, to avoid influence of determination accuracy of the spring constant and sphere radius on the obtained results. The thermodynamic work of adhesion was determined from the measured pull-off force using the Johnson-Kendall-Roberts (JKR) adhesion theory. Rabinovich's model was applied for the consideration of an effect of roughness when calculating the work of adhesion. It was found that the work of adhesion correlates with the hydrophilic properties of the PP surface and SAMs as well as with the polarity of the liquid medium. The observed correlations agree well with those found for the work of adhesion calculated from contact angle measurement.     

连续纤维增强含二氮杂萘酮联苯结构聚芳醚砜酮树脂基复合材料的界面

利用射频感性耦合冷等离子体(ICP)处理技术改性连续纤维表面,分别采用X射线光电子能谱(XPS)、原子力显微镜(AFM)及动态接触角分析(DCA)系统研究了等离子体处理时间、放电气压、放电功率等工艺参数对连续碳纤维、芳纶纤维和对亚苯基苯并二噁唑(PBO)纤维的表面化学成分、表面形貌、表面粗糙度及表面自由能的影响.研究结...     

Interfacial effect on photo-oxidation of PP via model blends

The interface in multiphase material plays an important role not only in mechanical properties, but also in aging behavior. This article uses polypropylene/polymethyl methacrylate (PP/PMMA) and polypropylene/polystyrene (PP/PS) blends (PMMA and PS as dispersion phase) as models to investigate the interfacial effect on the photo-oxidative aging of PP. The chemical property and stability of dispersed phase could make big difference on aging behavior of PP. PMMA, with polar functional group at the interface, accelerated the photo-oxidation of PP, while PS, with inert functional group at the interface, had little influence. Both the dispersion phases have little effects on crystallization of PP and the oxygen diffusion. The photo degradation product of PMMA could help to initiate or accelerate aging of PP mainly via free radicals transfer. Grafting reaction happened in the interface and the interfacial cohesion of PP and PMMA enhanced thereby.     

Polyurethane (urea)/polyacrylates interpenetrating polymer network (IPN) adhesives for low surface energy materials

On the basis of the polymerization of the acrylate phase catalyzed by the oxidation of trialkylborane at room temperature, a series of polyurethane (urea)/polyacrylates adhesives with interpenetrating polymer network structure (IPNS) was synthesized. The crosslinking polyurethane (urea) phase was synthesized by the reaction between polymer diamine or triol and isocyanate. The resulting IPN adhesives as a function of the polyurethane (urea) or 2‐hydroxylethyl acrylate terminated polyurethane (HEA‐PU) (crosslinking agent of acrylate phase) content were explored. The adhesive morphology took on the IPNS that manifested as a finely dispersed polyurethane (urea) phase in the acrylate phase. Excellent adhesion to low surface energy materials was achieved within a wide range of polyurethane (urea) contents. The IPN adhesives also displayed better flexibility than polyacrylate adhesives with HEA‐PU as a crosslinking agent. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantitative determination of interfacial adhesion in composites with strong bonding

An approach was proposed for the quantitative determination of adhesion strength in composites, in which adhesion is created by other mechanisms than secondary interactions. The approach is based upon a model, which gives debonding stress as a function of interfacial adhesion. Debonding stress was determined by acoustic emission experiments. The mechanism of deformation was checked by SEM experiments and the approach was verified on composites with known interfacial adhesion. The results showed that the use of functionalized polymer in PP/CaCO₃ composites resulted in adhesion strength one order of magnitude larger than without the coupling agent. The application of various surface modification techniques in PP/glass bead composites yielded different adhesion values covering a range of about one order of magnitude. The quantitative determination of interfacial adhesion makes possible the design and optimization of most surface modification techniques in particulate filled and short fiber reinforced composites.     

Surface properties of polypropylene following a novel industrial surface‐treatment process

Polypropylene (PP) is used in many automotive applications where good paint adhesion is of primary importance. PP is widely known for its low surface energy which impacts negatively on its adhesion strength. PP surfaces were modified using a new industrial surface‐treatment process known as the Accelerated Thermo‐molecular adhesion Process (ATmaP). ATmaP grafts functional groups to the polymer surface derived from an atomised and vapourised nitrogen‐containing coupling agent. The surface properties and adhesion performance of PP samples treated using the ATmaP process and two different flame processes were compared using XPS, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and mechanical testing (pull‐up tests). The latter showed that ATmaP improved adhesion strength significantly in comparison with conventional flame treatments. XPS showed an increase in oxygen and nitrogen concentration on the surface of ATmaP‐treated samples compared with untreated and flame‐treated samples. Principal components analysis (PCA) of the ToF‐SIMS data revealed the major phenomena occurring during the surface treatment of PP samples. Early stage events, including the chain scission of the PP backbone chain and the subsequent reaction of these chains with the surrounding air, are captured by the first principal component (PC1). The increase in the concentration of NO surface functional groups resulting from ATmaP treatment is captured by the second principal component (PC2). Copyright © 2008 John Wiley & Sons, Ltd.     

Surface Modification of Polyester Monofilaments by Atmospheric-Pressure Nitrogen Plasma

Polyester monofilaments were treated by a pulsed surface electrical discharge in nitrogen at atmospheric pressure, to increase their adhesion to an epoxy resin matrix. The treatment resulted in an eight-fold increase in adhesive strength, without any change in mechanical properties of the monofilaments. It is concluded that polar group interactions, rather than increased surface area, are responsible for the improved adhesive strength.     

Solvatochromism as an alternative for contact angle measurements in the characterisation of modified polymer surfaces

Polyolefine surfaces have been pre-treated by UV/ozone and UV/water methods. The increase in polar groups on a polymer surface and the contribution of these polar groups to the adhesion of the polymer has been investigated by using contact angles and tensile strength tests. Because contact angle measurements do not give information about the specific polar groups on the surface we have used solvatochromic analyses to identify specific polar groups. The results showed that solvatochromic analyses is a promising method to discriminate between different kinds of polar groups and therefore solvatochromic surface characterisation may become an important surface analytical tool in adhesive technology.     

Interfacial rheology of protein–surfactant mixtures

The distribution of proteins and surfactants at fluid interfaces (air–water and oil–water) is determined by the competitive adsorption between the two types of emulsifiers and by the nature of the protein–surfactant interactions, both at the interface and in the bulk phase, with a pronounced impact on the interfacial rheological properties of these systems. Therefore, the interfacial rheology is of practical importance for food dispersion (emulsion or foam) formulation, texture, and stability. In this review, the existence of protein–surfactant interactions, the mechanical behaviour and/or the composition of emulsifiers at the interface are indirectly determined by interfacial rheology of the mixed films. The effect on the interfacial rheology of protein–surfactant mixed films of the protein, the surfactant, the interface and bulk compositions, the method of formation of the interfacial film, the interactions between film forming components, and the displacement of protein by surfactant have been analysed. The last section tries to understand the role of interfacial rheology of protein–surfactant mixed films on food dispersion formation and stability. The emphasis of the present review is on the interfacial dilatational rheology.     

A novel technique for the interfacial characterisation of glass fibre–polypropylene systems

In the present work, a new technique was developed to determine the interfacial properties of two opaque glass fibre/polypropylene (GF/PP) systems via fragmentation tests on single filament model composites. Fragmentation tests usually require the fibre inside the composites to be completely aligned in the loading direction. Since PP matrices are non-transparent, it is not possible to guarantee a priori this condition. Hence, a novel technique was developed to determine the inclination of the filaments embedded in the composites. The fibre–polymer systems were also evaluated by comparing their interfacial properties with the overall mechanical properties determined on pultruded GF/PP composites. The present work shows that the knowledge of the interfacial properties is important, not only to compare alternative fibre/matrix systems, but also to assess whether the level of adhesion in these systems is adequate to fabricate composites with good mechanical properties.