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Thermoplastic polyurethane-fumed silica composites: Influence of the specific surface area of fumed silica on the viscoelastic and adhesion properties
Abstract
Fumed silicas of different specific surface area (90-380 m/g) were added to a thermoplastic polyurethane (PU) solution. After solvent removal, solid fumed silica-PU composites were obtained. The viscoelastic properties of PU were improved by adding fumed silica and only a solid-like behavior in PU-fumed silica composites was obtained. The increase in the specific surface area of the fumed silica up to 200 m / g increased the moduli of the composites. Fumed silica-PU interactions were responsible for the improved rheological properties of the composites. The activation energies for viscous flow of the composites were 14-16 kcal/mol and increased as the specific surface area of fumed silica increased. The glass transition temperature (obtained from DMTA and DSC experiments) and the crystallization rate of fumed silica-PU composites decreased compared with PU and also decreased with increasing surface area of the fumed silica. The contact angle values were similar in all the composites and the strength of PVC/fumed silica-PU composite joints was not affected by the specific surface area of the fumed silica.
... For underfill materials in case of solder flip chip assembly, high modulus is needed to effectively redistribute the solder joints stress to the chip and substrate through the assembly warpage 3) . Similarily, since NCP materials assembled on an organic substrate function as both underfill and die adhesive, higher modulus by adding high content of silica filler is needed. ...
... Chip length Shear modulus of layer i Flexural rigidity of layer i D = D 1 +D 2 +D 3 Flexural rigidity t = t 1 +t 2 +t 3 Assembly thickness ...
... Chip length Shear modulus of layer i Flexural rigidity of layer i D = D 1 +D 2 +D 3 Flexural rigidity t = t 1 +t 2 +t 3 Assembly thickness ...
In this paper, thermo-mechanical and rheological properties of NCPs (Non-Conductive Pastes) depending on silica filler contents and diluent contents were investigated. And then, thermal cycling (T/C) reliability of flip chip assembly using selected NCPs was verified. As the silica filler content increased, thermo-mechanical properties of NCPs were changed. The higher the silica filler content was added, glass transition temperature (Tg) and storage modulus at room temperature became higher. While, coefficient of thermal expansion (CTE) decreased. On the other hand, rheological properties of NCPs were significantly affected by diluent content. As the diluent content increased, viscosity of NCP decreased and thixotropic index increased. However, the addition of diluent deteriorated thermo-mechanical properties such as modulus, CTE, and Tg. Based on these results, three candidates of NCPs with various silica filler and diluent contents were selected as adhesives for reliability test of flip chip assemblies. T/ C reliability test was performed by measuring changes of NCP bump connection resistance. Results showed that flip chip assembly using NCP with lower CTE and higher modulus exhibited better T/C reliability behavior because of reduced shear strain in NCP adhesive layer.
... Fumed silica is a well-known mineral filler for epoxy and polyurethane adhesives [35]. The addition of nanosilica to polyurethane adhesives improves their adhesion and rheological properties [35][36][37][38][39]. Moreover, many studies have been conducted on polyurethane/nanosilica composites. ...
... The amount of phase separation can be reduced by decorating silanol groups on the surface of silica nanoparticles that form a strong hydrogen bonding and increase the T g of the nanocomposites. [96] Beloqui et al. [97] evaluated the influence of surface area of fumed silica particles on the rheological and thermal properties of TPU. The storage modulus of the TPU is particularly higher when incorporated with silica and susceptible to its surface area up to 200 m 2 /g, thereafter there was no noticeable change observed. ...
Thermoplastic polyurethane (TPU) reinforced with natural or renewable fillers gained significant attention in the scientific community and industries. The properties of TPU can be tailored using different reinforcements or blends to enhance its performance and elevate the potential applications of the composite. Besides, composites offer eco-friendliness, recyclability, and biocompatibility
thus overcoming the environmental concerns. However, the manufacturing in mass quantity and upholding the quality of these composites has remained one of the principal challenges. Herein, we critically highlighted an overview of the current comprehension of the various ecofriendly and renewable fillers/fibers reinforced in TPU composites for tuning the mechanical and thermal properties of TPU. Some of the important research articles that discuss the influence of interactions, morphology, and modification/treatment of fillers are contained within to understand the behavior and consequence of reinforcements on the physical properties of TPU composites.
... Fumed silicas (nanosilicas) are fillers commonly added to improve the thermal, rheological and mechanical properties of TPU´s [2][3][4][5][6][7]. This improvement in properties has been previously ascribed to the creation of hydrogen bonds between the hydroxyl groups on the nanosilica surface and the soft segments of the polyurethane, favoring the degree of phase separation [8][9][10][11]. ...
Abstract
Nanosilicas with different silanol contents were obtained by treatment of hydrophilic fumed
silica with dimethyldichlorosilane. This treatment reduced the silanol content and produced
the particle agglomeration of the nanosilicas. Thermoplastic polyurethane (TPU) adhesives
containing nanosilicas were prepared and characterized by FTIR spectroscopy, differential
scanning calorimetry (DSC), plate–plate rheology, dynamic mechanical thermal analysis
(DMTA) and transmission electron microscopy (TEM).
It was demonstrated that addition of hydrophilic nanosilicas favored the degree of phase
separation between the hard (i.e. isocyanate + chain extender) and soft (i.e. polyol)
segments in the TPUs; the higher the silanol content on the surface of silica, the higher the
degree of phase separation, and the crystallinity of the polyurethane (due to the soft
segments) was also increased. Hydrogen bonds between the ester carbonyl groups in the
TPU and the silanol groups on the silica surface were created and more favored by
increasing the silanol content.
... Aubrey [18] discussed the mechanism of adhesion of various pressure sensitive adhesives containing tackifying resins. Jauregui-Beloqui et al. [19] described the importance of fumed silica in the improvement of peel strength of polyurethane-fumed silica composites without affecting the surface characteristics. ...
In this study, a definite ratio of 2-ethylhexyl acrylate/acrylic acid/methyl methacrylate (2-EHA/AA/MMA) monomers was considered for the preparation of latexes via miniemulsion polymerization with applicability in pressure sensitive adhesives. Then latexes containing 0 to 4 wt% of nanosilica were prepared and their characteristics were studied. The presence of nanosilica particles in the final product was verified and its content was measured through ICP and TGA analyses. Particle size and morphological properties were studied by DLS, SEM and TEM analyses and finally rheological and adhesion properties of the samples were discussed. It was found that in the presence of nanosilica, larger particles ranging from 68 up to 152 nm with wider distribution were obtained. The results revealed that silica particles have been located in the shell of latex particles due to their hydrophilic characteristics. Also silica nanoparticles are incorporated in the polymeric particles entirely by comparing the results of ICP and TGA analyses. Rheological studies showed that by increasing the amount of nanosilica, elastic and loss modulus and also viscosity have been increased. Further investigations on the adhesion properties such as tack, peel and shear strength showed a considerable improvement in tack resistance up to 300% for the nanocomposite films containing 4 wt% of nanosilica.
... Fumed silicas (nanosilicas) are fillers commonly added to improve the thermal, rheological and mechanical properties of TPU´s [2][3][4][5][6][7]. This improvement in properties has been previously ascribed to the creation of hydrogen bonds between the hydroxyl groups on the nanosilica surface and the soft segments of the polyurethane, favoring the degree of phase separation [8][9][10][11]. ...
Thermoplastic polyurethanes (TPUs) are multi-phase segmented polymers that exhibit a two-phase microstructure (phase separation), which arises from the incompatibility between the soft and the hard segments. The hard rigid segment segregates into a glassy or semicrystalline domain, and the polyol soft segments form amorphous or rubbery matrices in which the hard segments are dispersed [1]. Fumed silicas (nanosilicas) are fillers commonly added to improve the thermal, rheological and mechanical properties of TPU´s [2–7]. This improvement in properties has been previously ascribed to the creation of hydrogen bonds between the hydroxyl groups on the nanosilica surface and the soft segments of the polyurethane, favoring the degree of phase separation [8–11]. Previous experimental evidence [12, 16-20] has corroborated the formation of hydrogen bonds between the nanosilica and the polyurethane. To analyze in depth the creation of hydrogen bonds between the nanosilica and the polyurethane and its incidence in the structure and properties of TPU´s, nanosilicas with different silanol contents were added to thermoplastic polyurethanes. Specific surface area is inversely related to the primary particle size of nanosilica, and the greater the specific surface area the greater the silanol content. If hydrogen bond formation is responsible for improving the properties of nanosilica–polyurethane mixtures, it can be expected that the greater the silanol content in the nanosilica, the more noticeable the extent of phase separation in the polyurethane should be; therefore, 2wt% of different nanosilicas was added to a TPU and the mixtures obtained were characterized by FTIR spectroscopy, DSC, X-ray diffraction, plate–plate rheometry, adhesion tests, DMTA and TEM.
... And this is presumably due to the high interface area of silica/polymer, when high content of silica fillers are added. [8] For underfill materials of solder ball flip chip assembly, high modulus is needed to effectively redistribute the solder joints stress to the chip and substrate through the assembly warpage [9]. Similarily, since ACA materials assembled on an organic substrate function as both underfill and electrical conductor, high modulus of ACA by adding high content of fillers is needed. ...
Flip chip assembly on organic substrates using ACAs have received much attentions due to many advantages such as easier processing, good electrical performance, lower cost, and low temperature processing compatible with organic substrates. ACAs are generally composed of epoxy polymer resin and small amount of conductive fillers (less than 10 wt.%). As a result, ACAs have almost the same CTE values as an epoxy material itself which are higher than conventional underfill materials which contains lots of fillers. Therefore, it is necessary to lower the CTE value of ACAs to obtain more reliable flip chip assembly on organic substrates using ACAs. To modify the ACA composite materials with some amount of conductive fillers, non-conductive fillers were incorporated into ACAs. In this paper, we investigated the effect of fillers on the thermo-mechanical properties of modified ACA composite materials and the reliability of flip chip assembly on organic substrates using modified ACA composite materials. Contact resistance changes were measured during reliability tests such as thermal cycling, high humidity and temperature, and high temperature at dry condition. It was observed that reliability results were significantly affected by CTEs of ACA materials especially at the thermal cycling test. Results showed that flip chip assembly using modified ACA composites with lower CTEs and higher modulus by loading non-conducting fillers exhibited better contact resistance behavior than conventional ACAs without non-conducting fillers Microwave model and high-frequency measurement of the ACF flip-chip interconnection is investigated using a microwave network analysis. ACF flip chip interconnection has only below 0.1nH, and very stable up to 13 GHz. Over the 13 GHz, there was significant loss because of epoxy capacitance of ACF. However, the addition of SiO2 filler to the ACF lowered the dielectric constant of the ACF materials resulting in an increase of resonance frequency up to 15 GHz. Our results indicate that the electrical performance of ACF combined with electroless Ni/Au bump interconnection is comparable to that of solder joint.
... The modulus of the ACF materials, particularly the storage modulus, increases as the silica content increases at room temperature, and the modulus decreases as the temperature increases. For underfill materials of the solder ball flip chip assembly, we need high modulus to effectively redistribute the stress of the solder joints to the chip and substrate through the assembly warpage [11]. Similarly, because the ACF materials assembled on an organic substrate must function as both the underfill and the electrical conductor, we need a high filler content to ensure a high ACF modulus. ...
Anisotropic conductive adhesives (ACAs) are as promising interconnect materials for flip chip assembly in low cost, high-density, high-speed interconnection packages. We evaluated and compared several flip chip interconnects that use ACAs at the radio frequency (RF) and high-frequency range. The performance of high-speed circuits is limited by the package interconnect discontinuity which is due to large inductance and resistance in the high-frequency range. This discontinuity is determined by the interconnection geometry and materials used. For bumps on the integrated circuit (IC), we used Au studs, Au electroplated and electroless Ni/Au bumps, for the interconnection adhesives, we used two kinds of anisotropic conductive film (ACF) with a different dielectric constant. To evaluate the high frequency model parameters, which we based on an ACF flip chip model and network analysis, we took the high-frequency measurements of test flip chip vehicles that used different bonding materials. Furthermore, to demonstrate real applications for an ACF interconnection at the RF and high-frequency range, we applied ACF flip chip technologies to assemble a passive device that uses an RF integrated passive device. We also applied these technologies to an active device that uses a highly integrated monolithic microwave (IC) device on an RF module. Moreover, we compared the high-frequency characteristics of these devices with those of flip chip assemblies fabricated with conventional methods such as solder ball interconnection.
... For underfill materials in case of solder flip chip assembly, high modulus is needed to effectively redistribute the solder joints stress to the chip and substrate through the assembly warpage [3]. Similarly, since NCP materials assembled on an organic substrate function as both underfill and die adhesive, higher modulus by adding high content of silica filler is needed. ...
In this paper, thermomechanical and rheological properties of nonconductive pastes (NCPs) depending on silica filler contents and diluent contents were investigated. And then, thermal cycling (T/C) reliability of flip chip assembly using selected NCPs was verified. As the silica filler content increased, thermomechanical properties of NCPs were changed. The higher the silica filler content was added, glass transition temperature (Tg) and storage modulus at room temperature became higher while coefficient of thermal expansion (CTE) decreased. On the other hand, rheological properties of NCPs were significantly affected by diluent content. As the diluent content increased, viscosity of NCP decreased and thixotropic index increased. However, the addition of diluent deteriorated thermomechanical properties such as modulus, CTE, and Tg. Based on these results, three candidates of NCPs with various silica filler and diluent contents were selected and used as adhesives for reliability test of flip chip assemblies. T/C reliability test was performed by measuring changes of NCP bump connection resistance. Results showed that flip chip assembly using NCP with lower CTE and higher modulus exhibited better T/C reliability behavior because of reduced shear strain in NCP adhesive layer.
... For underfill materials of solder ball flip chip assembly, high modulus is needed to effectively redistribute the solder joints stress to the chip and substrate through the assembly warpage [9]. Similarly, since ACA materials assembled on an organic substrate function as both underfill and electrical conductor, high modulus of ACA by adding high content of fillers is needed. ...
We investigated the effect of nonconducting fillers on the
thermomechanical properties of modified anisotropic conductive adhesive
(ACA) composite materials and the reliability of flip chip assembly on
organic substrates using modified ACA composite materials. For the
characterization of modified ACAs composites with different content of
nonconducting fillers, dynamic scanning calorimetry (DSC),
thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and
thermomechanical analysis (TMA) were utilized. As the nonconducting
filler content increased, CTE values decreased and storage modulus at
room temperature increased. In addition, the increase in the content of
filler brought about the increase of Tg(DSC) and
Tg(TMA). However, the TGA behaviors stayed almost the same.
Contact resistance changes were measured during reliability tests such
as thermal cycling, high humidity and temperature, and high temperature
at dry condition. The reliability results were significantly influenced
by CTEs of ACA materials, especially at the thermal cycling tests.
Results showed that flip chip assembly using modified ACA composites
with lower coefficients of thermal expansion (CTEs) and higher modulus
by loading nonconducting fillers exhibited better contact resistance
behavior than conventional ACAs without nonconducting fillers
The basic aim of the research work is to expand the application range of biomaterials in the field of medical by increasing antibacterial and biocompatible behavior of thermoplastic polyurethanes. Blends of thermoplastic polyurethanes with chitosan and starch were prepared through extrusion process. The effect of polysaccharides (corn starch and chitosan) incorporation in thermoplastic polyurethane matrix and polymers interaction on thermal and morphological aspects was investigated. Possible interaction among chitosan and starch within TPU matrix individually and together in a blend were assessed by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffractometer (XRD). The results indicated that thermoplastic polyurethanes were semi crystalline in nature whereas hydrophilicity of prepared thermoplastic polyurethanes was determined by contact angle. Biological properties endowed that TPU blended with chitosan and starch possessed antibacterial and hemolytic potential. Hence, it can be a suitable candidate for biomedical applications.
This chapter is one of the very few reviews in the existing literature on shoe bonding and is mainly focussed in providing an updated overview of the upper-to-sole bonding by means of adhesives. Because the previous chapter of this book on shoe bonding (Martín-Martínez, 2005 [1]) dated from 2005, it is timely to give an updated revision in which the most recent literature is compiled. The surface preparation of the rubber and polymeric soles and the formulations of the polyurethane and polychloroprene adhesives used in shoe bonding have been updated, and they will be revised separately in the following sections.
In this paper, the high frequency properties of anisotropic conductive films (ACFs) in flip chip interconnects at the RF and high-frequency range were investigated. To evaluate the high frequency model parameters, which are based on an ACF flip chip model and a network analysis, high-frequency measurements of test flip chip vehicles that used different bonding materials were evaluated. Furthermore, to demonstrate real applications for an ACF interconnection at the RF and high-frequency range, ACF flip chip technologies were applied to assemble a passive device that uses an RF integrated passive device, and also, an active device that uses a highly integrated monolithic microwave integrated circuit device on an RF module. Furthermore, the high-frequency characteristics of these devices with those of flip chip assemblies fabricated via conventional methods such as solder ball interconnection were compared.
Yam and cocoyam were characterized to determine the content of starch gelatinization temperatures and the size of their granules. Percentage of soluble solids and content of dextrins obtained at different reaction times was also estimated. Adhesives obtained from yam and cocoyam starch were characterized by a peeling test. Mixtures of starch from yam and commercial sources with different percentages (wt.%) of yam (10, 25, 37 and 50), were prepared and characterized by using a peeling test. Adhesive containing 37 wt% of yam showed higher resistance in the peeling test.
This study focused on achieving biodegradable thermoplastic polyurethane (TPU) blends with good mechanical properties by the incorporation of starch. Thermoplastic starch (TPS) was developed by plasticizing corn starch in a twin screw. Polyolefin elastomer (POE) was used as the compatibilizer to improve the flexibility of the TPU/TPS system. The miscibility of the blends was investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Mechanical analysis (impact, tensile, and folding endurance tests), dynamic mechanical analysis (DMA), degradation tests and contact angle (CA) tests were employed to study the mechanical properties and hydrophilic sensitivity of the TPU/TPS blends. The results showed that POE improved the miscibility of the blends by enhancing the interfacial effects of the TPU/TPS blend, decreasing the interfacial tension between TPS and TPU, as well as increasing the inter-hydrogen bonds between TPU and TPS. The hydrophilic qualities of the TPU blends, such as water adsorption and CA, increased with increasing TPS content, resulting in improved biodegradation ability. TPU/TPS (20 wt%)/POE (10 wt%) endowed the blends with good folding endurance (>30.0 × 103), notched impact strength (no break), elongation at break (>800%) and a 6.2% biodegradation rate after 7 weeks. The improved properties of TPU/TPS showed that these blends have high potential for use in environmentally friendly materials.
Anisotropic conductive adhesives have been considered and evaluated as promising interconnect materials for flip chip assembly in the applications for low cost, high-density and high speed interconnection packages, In this paper, we have evaluated and compared several flip chip interconnects using anisotropic conductive adhesives at RF and high frequency range. The performances of high-speed circuits are limited by package interconnect discontinuity due to large inductance and resistance in the high frequency range. This discontinuity is determined by the interconnection geometry and materials used. For bumps on the IC, Art stud, An electroplated and electroless Ni/Au were used, and for the interconnection adhesives, two kinds of ACFs with different dielectric constant were used. The high frequency measurements were performed on the test flip chip vehicles using different bonding materials to evaluate high frequency model parameters based upon ACF flip chip model and network analysis. We applied these ACFs flip chip technologies to the assemblies of passive device using RF IPD (Integrated Passive Device) and active device using RF active MMIC device on RF module to demonstrate real applications of ACF interconnection at RF and high frequency range, and compared the results with those of flip chip assembles using conventional methods such as solder ball interconnection. The reliability of ACF flip chip interconnects was also investigated by various environmental tests, such as thermal cycling test (-55 degreesC/+125 degreesC, 1000 cycle), high temperature humidity test (85 degreesC/85%RH, 1000 hours) and high temperature storage test (150 degreesC, dry condition) to evaluate the effect of environmental attacks on the electrical stability of ACF flip chip assemblies.
This chapter constitutes one of the very few reviews in the existing literature on shoe bonding, and it gives an updated overview of the upper to sole bonding by means of adhesives. The surface preparation of rubber soles and both the formulations of polyurethane and polychloroprene adhesives are described in more detail. The preparation of adhesive joints and adhesion tests are also revised. Finally, the most recent development and technology in shoe bonding is described.
Nanocomposites consisting of thermoplastic polyurethane-urea (TPU) and silica nanoparticles of various size and filler loadings were prepared by solution blending and extensively characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermal analysis, tensile tests, and nanoindentation. TPU copolymer was based on a cycloaliphatic diisocyanate and poly(tetramethylene oxide) (PTMO-2000) soft segments and had urea hard segment content of 20% by weight. TPU/silica nanocomposites using silica particles of different size (29, 74 and 215 nm) and at different loadings (1, 5, 10, 20 and 40 wt. %) were prepared and characterized. Solution blending using isopropyl alcohol resulted in even distribution of silica nanoparticles in the polyurethane-urea matrix. FTIR spectroscopy indicated strong interactions between silica particles and polyether segments. Incorporation of silica nanoparticles of smaller size led to higher modulus and tensile strength of the nanocomposites, and elastomeric properties were retained. Increased filler content of up to about 20 wt. % resulted in materials with higher elastic moduli and tensile strength while the glass transition temperature remained the same. The fracture toughness increased relative to neat TPU regardless of the silica particle size. Improvements in tensile properties of the nanocomposites, particularly at intermediate silica loading levels and smaller particle size, are attributed to the interactions between the surface of silica nanoparticles and ether linkages of the polyether segments of the copolymers.
In this study, the effect of nanosilica and boron carbide on the adhesion strength of a phenolic resin for graphite bonding was studied. The adhered specimens were cured at 250 degrees C and then heat treated to examine the thermal resistance in the range 200-1000 degrees C. Then, the adhesion strength of specimens was examined by a tensile method. The chemical structure of bonding and possible carbonization was examined using Fourier transform infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) was employed to determine the char yield, and X-ray diffraction (XRD) was used to study crystalline phases at different temperatures. The elemental analysis and morphology of the adhesive bond were investigated using energy-dispersive Xray spectroscopy (EDS) and scanning electron microscopy (SEM), respectively. The results showed that sintering of reformed boron carbide and amorphous carbon above 800 degrees C resulted in a significant increasing in adhesion strength at 1000 degrees C.
A series of acrylic co-polymers and terpolymers from ethyl acrylate (EA), butyl acrylate (BA) and acrylic acid (AA) were synthesized by solution polymerization. Nanocomposite adhesives based on these acrylic polymers and silica or clay were prepared by sol–gel or solution blending techniques, respectively. The effect of nanoparticles on the performance of the hybrid adhesives was investigated by measuring peel strength, lap shear strength or static shear resistance against three substrates having different surface characteristics- aluminum (Al), wood (W) and biaxially oriented polypropylene (PP). The results showed significant improvement in peel strength of Al–Al and PP–PP joints with increase in polarity of the polymer matrix and nanofiller concentration. These results could be explained in terms of higher cohesive strength of the nanocomposite adhesives. The locus of failure also changed from interfacial failure for neat acrylic adhesive to stick–slip failure for the hybrid composites. Both the lap shear strength and static shear resistance of the hybrid nanocomposites also gradually increased with nanofiller loading. Al–Al and W–W joints displayed higher joint strength, because of the interaction of the hydroxyl groups present on the surface of these substrates.
—Both fumed silica and sepiolite have been used as a filler of polyurethane (PU) adhesives. Although effective, the small particle size and the relative high cost of fumed silica are limitations in some applications. Sepiolite is cheaper than fumed silica, but its relatively large particle size facilitates its settling from the adhesive solutions. In this study, the usefulness of using sepiolite + fumed silica mixtures as a filler in solvent-based PU adhesives is demonstrated. The rheological and adhesion properties of the PU adhesive solutions and the rheological and mechanical properties of the PU films (without solvent) were studied. SEM micrographs of PU films showed the morphology and compatibility of the fillers with the PU matrix. The use of sepiolite + fumed silica mixtures inhibited the settlement of the filler from the PU adhesive solutions, increased both the storage and the loss moduli, and improved the rheological and mechanical properties of the PU. On the other hand, the green (immediate) T-peel strengths of roughened styrene-butadiene rubber/PU adhesive joints and plasticized PVC/PU adhesive joints were greatly improved in filled PU adhesives. The effects produced by using fumed silica alone or sepiolite + fumed silica mixtures were very similar, although in general, somewhat more marked in fumed silica-filled PU.
Thermoplastic polyurethane (TPU) adhesives containing nanosilicas with different specific surface area and silanol group content were prepared and characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TGA), X-ray diffraction, plate-plate rheology, dynamical–mechanical–thermal analysis (DMTA), transmission electron microscopy (TEM), and strain–stress test. Adhesive strength was obtained from T-peel tests of PVC/polyurethane adhesive joints.Formation of agglomerates of nanosilica particles within the polyurethane matrix were favoured by increasing the silanol content likely due to stronger hydrogen bond interactions between the silanol groups on the nanosilica over those between the polyurethane and the nanosilica. As a consequence, inter-urethane bonds formation rather than ester-urethane bonds were favoured, leaving the soft segment chains more free to interact between them. Thus, addition of nanosilica favoured the phase segregation in the thermoplastic polyurethane. The increase in specific surface area and silanol content in the nanosilica, generally enhanced the degree of phase separation in the polyurethane, being less marked for nanosilicas with more than 200m2/g and 0.60mmol SiOH/gsilica. On the other hand, the addition of the nanosilica improved the tensile strength and elongation at break, and the viscoelastic properties of the polyurethane. The immediate adhesive strength of PVC/polyurethane adhesive joints increased in the filled adhesives and it was determined by the rheological properties of the polyurethane–nanosilica mixtures. By increasing the time after joint formation, the crystallization of the polyurethane was produced giving higher adhesive strength and although a cohesive failure in the PVC was always obtained, a slight though progressive increase in joint strength was found with the passage of time with the ordering of the three systems (PU-0.45, PU-0.60 and PU-0.90) remaining unchanged with the PU-0.60 system the stronger and the PU-0.90 system the weaker. This is in agreement with the trends in the viscoelastic and mechanical properties of the filled adhesives.
The way of addition of fumed silica determined the rheological properties of polyurethane (PU) adhesives. The higher the shear rate during preparation of fumed silica containingPU adhesives, the higher viscosity and improved plasticity and thixotropy in the solutions. The improved properties of these adhesive solutions were ascribed to the creation of interactions between the silanol groups on the fumed silica, the polar groups in the soft segments of the polyurethane and/or the solvent. However, the way of incorporate the fumed silica in the polyurethane did not affect the rheological properties of fumed silica-PU composites (obtained by solvent removal from the solutions), indicating the key role of the solvent in the rheology of PU adhesive solutions.
In light of the success of making multicomponent sol–gel glasses, in this study the synthesis of new hybrid nanosilicas with controlled hydrophilic/hydrophobic properties was carried out by incorporating organic based species with appropriate functional groups to inorganic based alkoxides by co-condensation reaction. Furthermore, in this study the acidity and the water content during reaction synthesis was proven to be critical in controlling the structure of the hybrid nanosilicas. These nanosilicas with different hydrophobicity were obtained by using TEOS (tetraethylorthosilicate) and 10 wt% two organic modifiers (tris-hydroxymethylaminomethane — TRIS — and 1,1,1,3,3,3-hexamethyldisilazane-HDMS). The average diameter of the nano-particles ranged between 7 and 10 nm. The addition of the organic modifiers changed the pH of the hybrid nanosilicas, to a different extent depending on the nature of the organic modifier. The hydrophobicity in the hybrid nanosilicas estimated from pH measurements in water and ethanol, and from IR spectroscopy, can be tailored by incorporating different organic modifiers on the network during synthesis. Finally, the measurement of pH of the hybrid nanosilicas by using solvents with different polarity/acidity was a simple and efficient method of assessing the hydrophobicity of the nanosilicas.
Three nanosilicas with different silanol contents were prepared by treatment of hydrophilic fumed silica with dimethyldichlorosilane. This treatment reduced the silanol content and produced the particle agglomeration of the nanosilicas. Thermoplastic polyurethane (TPU) adhesives containing nanosilicas were prepared and characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), plate–plate rheology, dynamic mechanical thermal analysis (DMTA), transmission electron microscopy (TEM) and stress–strain testing. Adhesive strength was obtained from T-peel tests of PVC/polyurethane adhesive joints.The addition of hydrophilic nanosilicas favoured the degree of phase separation between the hard (i.e. isocyanate+chain extender) and soft (i.e. polyol) segments in the TPUs; the higher the silanol content on the surface of silica, the higher the degree of phase separation, and the crystallinity of the polyurethane (due to the soft segments) was also increased. Hydrogen bonds between the ester carbonyl groups in the TPU and the silanol groups on the silica surface were created and more favoured by increasing the silanol content. The tensile strength increased and the elongation at break of the polyurethane decreased by increasing the silanol content of the nanosilica. Addition of nanosilica increased the immediate adhesion of the polyurethane adhesives to PVC, irrespective of the silanol content on the nanosilica. The higher the mechanical and the rheological properties of the polyurethanes containing nanosilicas with different silanol content, the higher the final adhesive strength.
Fumed nanosilicas with different degree of silanization were used to obtain nanosilica-polyurethane (TPU) composites to modify their rheological and mechanical properties. The higher the silanol content of the nanosilica, the higher the storage modulus and the thermal stability of the silica-TPU composite. DMTA experiments confirmed that the TPU-silica interactions increased by increasing the silanol content of the nanosilica.
Polyimide–silica nanocomposites were synthesized with 4,4′-oxydianiline, 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride), and fluorine-modified silica nanoparticles. Fluorinated precursors such as 4″,4‴-(hexafluoroisopropylidene)bis(4-phenoxyaniline) (6FBPA) and 4,4′-(hexafluoroisopropylindene)diphenol (BISAF) were employed to modify the surface of the silica nanoparticles. The microstructures and thermal, mechanical, and dielectric properties of the polyimide–silica nanocomposites were investigated. An improvement in the thermal stability and storage modulus of the polyimide nanocomposites due to the addition of the modified silica nanoparticles was observed. The microstructures of the polyimide–silica nanocomposites containing 6FBPA-modified silica exhibited more uniformity than those of the nanocomposites containing BISAF-modified silica. The dielectric constants of the polyimide were considerably reduced by the incorporation of pristine silica or 6FBPA-modified silica but not BISAF-modified silica. The addition of a modifier with higher fluorine contents did not ensure a lower dielectric constant. The uniformity of the silica distribution, manipulated by the reactivity of the modifier, played an important role in the reduction of the dielectric constant. Using 6FBPA-modified silica nanoparticles demonstrated an effective way of synthesizing low-dielectric-constant polyimide–silica nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 882–890, 2007
DGEBA-based epoxy nanocomposites filled with various amounts of fumed silica nanopowders (10, 20 and 30 phr corresponding to 3.3, 6.4 and 9.2% by volume) were prepared by a solvent assisted dispersion procedure. The obtained nanocomposites were analyzed by means of differential scanning calorimetry, dynamic-mechanical thermal analysis, uniaxial tensile tests on un-notched samples and three-point bending tests on notched samples.All the thermal and mechanical properties showed non-monotonic trends with relative minima as the silica content increased. A trend inversion in the physical properties was detected at the highest filler level tested, which was not previously observed for epoxy systems filled with comparable amounts of unmodified silica. The behavior could be explained by considering a reduction of cross-linking degree of the epoxy matrix due to the huge viscosity increase induced by the silica nanoparticles during composites preparation. On the other hand, the physical immobilization of the cross-linked matrix can be supposed to be responsible for the inversion of the properties trend at the highest filler level, which is presumably very close to the percolation threshold.
Flip chip assembly on organic board using anisotropic conductive films (ACFs) is gained more attention because of its many advantages. But to obtain more reliable flip chip assembly, it is necessary to have low coefficient of thermal expansion (CTE) value of ACFs. To control the CTE of ACF materials, non-conductive silica fillers were incorporated into ACFs. The effect of non-conductive silica filler content and size on cure kinetics and thermo-mechanical properties of ACFs was studied. Furthermore, filler content and size effects on reliability of flip chip assembly using ACFs were also investigated. In accordance with increasing filler content, curing peak temperature and storage modulus (E′) increased. But CTE decreased as the filler content increased. The effect of filler size on composite properties and assembly reliability showed similar tendency with the filler content effect. The smaller filler size was applied, the better composite properties and reliability were obtained. Conclusively, incorporation of non-conductive fillers, particularly in case of smaller size and higher content, in ACFs improves the material properties significantly, and as a result, flip chip assembly using ACFs is resulted in better reliability.
Processing of flame-made nanoparticles into polymers is reviewed including surface modification and compounding. Recent advances in combustion and aerosol science enable scalable synthesis of such nanoparticles way beyond today's commercially available nanostructured carbon black and fumed silica. As a result, sophisticated filler nanoparticles with closely controlled size, morphology (aggregates or agglomerates) and composition (segregated or mixed phases or nanothin coatings onto core particles) become available motivating research for their surface functionalization and dispersion. Emphasis is placed on nanocomposite mechanics and optics. Quantitative relations for optimal nanocomposite structure are presented: from the particle–polymer interface to the formation of a percolation network.
The kinetics of thermal degradation process on thermoplastic polyurethanes (TPUs) adhesives with hydrophilic nanosilicas was studied using isothermal thermogravimetric analysis within the temperature range from 360 degrees C to 460 degrees C in nitrogen. The effect of nanosilicas with different hydrophilic degree in the thermoplastic polyurethanes was investigated. It was found that the thermoxidative degradation of polyurethane-silica nanocomposites takes place in one step. An analysis of the isothermal methods to evaluate kinetic parameters of decomposition of solids from isothermal thermogravimetric data is presented. Patents WO07146353A2 and US20070292623A1 have some relevant information about the topic develop in this study, because the principle in both cases relies on the interactions between reactive groups in the polymer (TPUs) and the silanol in the silica nano-particles.
Flip chip assembly directly on organic boards offers
miniaturization of package size and reduced in interconnection
distances, resulting in a high performance and cost-competitive
packaging method. This paper describes the investigation of alternative
low cost flip-chip mounting processes using electroless Ni/Au bumps and
anisotropic conductive adhesives/films as an interconnection material on
organic boards such as FR-4. As bumps for flip chip, electroless Ni/Au
plating was performed and characterized for plating speed, surface
roughness, and elemental analysis as a function of plating condition.
High plating rate and surface planarity of the electroless Ni were
considered as requirements for ACA flip chip bumps. In order to obtain
high plating rate and low surface roughness, plating conditions were
determined by controlling complexing agents in electroless Ni solution.
Annealing effects on Ni bump characteristics showed that the formation
of crystalline Ni with Ni3P precipitation above 300°C
causes an increase in hardness and intrinsic stress, resulting in
reliability limitation. As an interconnect material, modified ACFs
composed of Ni conductive fillers for electrical conductor and
nonconductive inorganic fillers for modification of film properties such
as CTE and tensile strength were formulated for improved electrical and
mechanical properties of ACF interconnection. The thermal cycle life of
ACAs flip chip on organic boards was usually limited by the CTE mismatch
between chip and board. However, flip chip assembly on FR-4 boards using
modified ACAs almost doubled the thermal cycle life
Flip chip assembly on organic substrates using ACAs (anisotropic
conductive adhesives) has advantages such as easier processing, good
electrical performance, lower cost, green processes, and organic
substrate-compatible low temperature processing. ACAs are composed of
epoxy polymer resin and conductive fillers (less than 10 wt.%). ACAs
thus have almost the same CTE values as epoxy alone, which are higher
than conventional underfill materials with silica fillers. It is thus
necessary to lower the ACA CTE value for more reliable flip chip
assembly on organic substrates. New ACA composites with conductive and
nonconductive fillers were devised. In this paper, we studied the effect
of fillers on the thermo-mechanical properties of modified ACA
composites and the reliability of flip chip assembly on organic
substrates using modified ACAs and electroless Ni and Au stud bumps. As
nonconducting filler content increased, CTE values decreased and storage
modulus at room temperature increased. Contact resistance changes were
measured during reliability tests such as thermal cycling, high
humidity/temperature, and high temperature/dry test. It was noted that
lowering ACA CTEs greatly enhanced thermal cycling reliability. Results
also showed that flip chip assembly using modified ACAs with lower CTEs
and higher modulus exhibited slightly better contact resistance behavior
than conventional ACAs without nonconducting fillers. The greater
reliability of flip chip on organic substrates using the new ACAs can
lead to new low cost flip chip on organic substrate applications such as
smart cards, RF, memory devices, etc
Flip chip assembly on organic substrates using ACAs have received
much attention due to many advantages, such as easier processing, good
electrical performance, lower cost, and low temperature processing
compatible with organic substrates. ACAs are generally composed of epoxy
polymer resin and small amounts of conductive fillers (less than 10
wt.%). As a result, ACAs have almost the same CTE values as an epoxy
material itself, which are higher than conventional underfill materials
which contain lots of fillers. Therefore, it is necessary to lower the
CTE value of ACAs to obtain more reliable flip chip assembly on organic
substrates using ACAs. To modify the ACA composite materials with some
amount of conductive fillers, non-conductive fillers were incorporated
into ACAs. In this paper, we investigated the effect of fillers on the
thermo-mechanical properties of modified ACA composite materials and the
reliability of flip chip assembly on organic substrates using modified
ACA composite materials. For the characterization of modified ACAs
composites with different content of non-conducting fillers, dynamic
scanning calorimeter (DSC), and thermo-gravimetric analyzer (TGA),
dynamic mechanical analyzer (DMA), and thermomechanical analyzer (TMA)
were utilized. As the nonconducting filler content increased, CTE values
decreased and storage modulus at room temperature increased. In
addition, the increase in the content of filler brought about the
increase of TgDSC and TgTMA. However, the TGA
behaviors stayed almost the same. Contact resistance changes were
measured during reliability tests such as thermal cycling, high humidity
and temperature, and high temperature at dry condition. It was observed
that reliability results were significantly affected by CTEs of ACA
materials, especially in the thermal cycling test. Results showed that
flip chip assembly using modified ACA composites with lower CTEs and
higher modulus from loading non-conducting fillers exhibited better
contact resistance behavior than conventional ACAs without
non-conducting fillers
Five hydrophilic and two hydrophobic fumed silicas of different surface area and particle size were added to solvent based polyurethane adhesives. Silica addition produced a noticeable increase in the adhesive viscosity, imparted negative thixotropy, increased the storage modulus (G') and improved the green adhesion of chlorinated rubber/PU adhesive/chlorinated rubber joints. Those modifications were more pronounced in the adhesives which contain hydrophilic silicas.
Two hydrophilic and two hydrophobic fumed silicas of different characteristics were added to solvent-based polyurethane adhesives (PU). IR spectroscopy, contact angle measurements and rheology (viscosity measurements, determination of viscoelastic properties) were used to monitor the variation of properties of PU adhesives produced by addition of silica. Immediate (green) adhesion was determined by T-peel testing of halogenated synthetic rubber/PU adhesive/halogenated synthetic rubber joints. Silica addition produced a noticeable increase in the PU adhesive viscosity which can be related to the variation of viscoelastic properties. Viscosity of PU adhesives containing hydrophilic silica slightly increased with time after preparation; the increase was less significant in PU adhesives with hydrophilic silica. In the rheological studies, silica imparted shear thinning and negative thixotropy to PU adhesives due to a better dispersion of the silica in the polyurethane during shearing. The addition of silica produces an increase in the storage modulus (G') of PU adhesives, the values obtained being independent of the hydrophilic or hydrophobic nature of the fumed silica. The increase of G' and the changes in tan δ of PU adhesives containing silica corresponded to an improvement in the green adhesion properties of chlorinated rubber/PU adhesive/chlorinated rubber joints. In general, in disagreement with previous results, the presence of silica did affect the properties of solvent-based PU adhesives, but these properties were not dependent on the type of silica (hydrophobic or hydrophilic) used in this study.
L'interface charge-polymére des matériaux polymères á composants multiples joue un rôle fondamental pour toutes leurs propriétés. Le présent travail met en évidence l'importance qu'ont pour les propriétés des composites à base de polypropyléne et de sépiolite aussi bien l'adhésion interfaciale que la formation de structures ordonnées autour des particules. Les essais réalisés lors de cette étude prouvent que quand il y a variation des propriétés superficielles de la sépiolite sous l'effet de l'organophilisation à travers ses groupes silanols, son comportement thermique et dynamique varie.
The influence of the addition of silica (Aerosil-200) (5-25 wt%) to polyurethane adhesives on their adhesion properties with non-chlorinated and surface-chlorinated rubbers has been studied. The chlorinating agent was Trichloroisocyanuric acid (TIC) in 2-butanone solution at a concentration of between 1 and 9 wt%. In general, silica produced an increase in the adhesive viscosity and an improvement of green (immediate) peel strength (especially with chlorinated rubber). The best results were obtained for a silica content of 10-20 wt%. However, the addition of silica did not improve the peel strength after a thermal ageing process. Polyurethane adhesives containing silica undergo an improvement in their resistance to degradation by chlorine on the rubber surface. On the other hand, the chlorination of silica produces the rupture of Si-O bonds and the formation of Si-H and Si-Cl groups. Furthermore, the stirring speed (directly related to the dispersion) of silica into the adhesive is an important parameter which affects the viscosity and peel strength. A stirring speed of 1000 rpm gives the best silica dispersion.
Fumed silica is a well-known mineral filler of epoxy and polyurethane adhesives. Although effective, the small particle size and the relative high cost of fumed silicas suggest the need for an alternative filler. In this study, the usefulness of adding a natural hydrated magnesium silicate (sepiolite) as a new filler in solvent-based polyurethane (PU) adhesive formulations has been demonstrated. The rheological and adhesion performance of the sepiolite-filled PU adhesive was compared with that in PU adhesives containing fumed silicas. The addition of a filler to PU adhesives provided an increase in viscosity, imparted thixotropy and pseudoplasticity to the adhesive solution, produced an increase in storage and loss moduli, and improved the rheology of the PU. The mechanical properties of adhesive films were increased by adding filler, mainly with fumed silica. On the other hand, the immediate T-peel strength of roughened or (roughened + chlorinated) styrene-butadiene rubber/PU adhesive joints was greatly improved in filled PU adhesives. The effects produced by adding sepiolite or fumed silica to the adhesives were very similar, although in general more noticeable in fumed silica filled PU due to the formation of hydrogen bonds between the filler and the solvent and/or the polyurethane (in sepiolite-filled adhesives, van der Waals forces seemed to be responsible for the interactions between the filler and the solvent and/or polyurethane).
The dynamic mechanical behavior of carbon black filled polymers of styrene and butyl methacrylate was examined at low strain amplitude and frequency in order to minimize destruction of the composite structure and elucidate the basis of yield and plasticization observed in steady shear. For specific filled systems, both G′ and G″ became independent of frequency and temperature at low frequencies, consistent with a yield phenomenon and the formation of a carbon black network. On the other hand, although the high molecular weight polystyrene showed plasticization effects at higher shear rates in steady shear rheology, such, plasticization effects were never observed in dynamic mechanical analysts. Yield behavior was observed most readily for the low molecular weight polystyrene. Limiting moduli for filled polystyrenes were independent of temperature, whereas, for polybutyl methacrylate, were sensitive to temperature. It is suggested that an independent network of carbon black is strongest in the low molecular weight polystyrene and weakest in poly (butyl methacrylate).
A sepiolite silicate was heat-treated at 550 and 1000°C to modify its structure, and was used as a filler in a solvent-based polyurethane (PU) adhesive. The treated sepiolites were characterized by X-ray diffraction and infra-red spectroscopy, and it was observed that the water was irreversibly removed from the structure and pores of the sepiolite, changing the structure. The increase of temperature produced a collapse of the sepiolite structure. The rheological, mechanical, thermal and adhesion properties of the filled PU adhesives were measured. In general, the addition of treated sepiolite to PU adhesives resulted in a loss of adhesive properties with respect to the blank (PU adhesive with untreated sepiolite). The loss in properties was more noticeable as the treatment temperature increased. Thus the PU adhesives containing treated sepiolite had reduced rheological properties (lower viscosity, lower storage and loss moduli, and they did not provide thixotropy and pseudoplasticity to the solutions) with respect to the PU adhesive filled with untreated sepiolite. On the other hand, the addition of treated sepiolite decreased the mechanical and thermal mechanical properties of PU films. The T-peel strength of roughened and roughened + chlorinated (with 1 wt% trichloroisocyanuric acid in 2-butanone) styrene-butadiene rubber/PU adhesive joints was improved if the PU adhesive contained untreated sepiolite, but it decreased if the sepiolite was heat-treated. Interactions between the untreated sepiolite, the solvent and the polyurethane were responsible for the improved properties of PU adhesives. These interactions disappeared when the sepiolite was heat-treated, because of the destruction of the structure of the sepiolite and the removal of surface silanol groups.