Tensile properties and morphology of PP/EPDM/glass bead ternary composites

The tensile properties of three types of injection molded glass bead (GB) filled polypropylene (PP)/ethylene-propylene-diene monomer (EPDM) ternary composites have been determined at room temperature by using an Instron materials testing machine. The effects of the filler surface treatment, the glass bead (GBI) pretreated with a silane coupling agent and the EPDM (EPDM-MA) modified with a maleic anhydride, and the filler content on the tensile mechanical properties of the ternary PP composites have been investigated. The Young's modulus (E_c) increases while the yield stress (σ_yc) and tensile fracture strength (σ_bc) of the composites decrease with increasing the volume fraction of glass beads (ϕ_g) when the volume fraction of EPDM is constant (ϕ_e = 10%). The (E_c) values of PP/EPDM/GBI and ϵ_bc for PP/EPDM-MA/GB2 (no surface pretreated) systems are the highest at the same ϕ_g. The tensile fracture energy (E_bc) and tensile fracture strain (ϵ_bc) of PP/EPDM/GBI and PP/EPDM/GB2 systems appear to peak at ϕ_g = 25%. However, the E_bc and ϵ_bc of PP/EPDM-MA/GB2 system show little changes with increasing ϕ_g. The fracture surfaces of ternary composites have been examined in a scanning electron microscope. The correlation between the tensile properties and morphologies of these materials have been discussed.     

Mechanical properties and morphology of glass bead–filled polypropylene composites

The effects of the filler content and size on the mechanical properties such as tensile modulus, E_c, yield strength, σ_yc, and impact strength, S_IC, of glass bead–filled polypropylene (PP) composites have been investigated employing an Instron materials tester and a Ceast impact tester at room temperature. With increasing concentration of glass beads, E_c and S_IC increase, but σ_yc decreases non–linearly, within a filler volume fraction range of 0%−20%; under the same test conditions, the values of E_C and σ_yc for PP with bigger beads are somewhat lower than those of PP with smaller ones; the maximum values of S_IC for the composites are about 1.4 times as high as the unfilled PP; the interface between the matrix and the beads is a weak bond. The results indicate that the stiffness and the toughness of the PP composites are effectively improved by addition of glass beads.     

Tensile properties of hollow glass bead‐filled polypropylene composites

The tensile properties of polypropylene (PP) filled with hollow glass beads have been measured at room temperature to identify the effects of the particle contents, size and its distribution on them in the present article. The mean diameters of the fillers were 11, 35, and 70 μm, and they were named as TK10, TK35, and TK70 respectively. The surface of these particles was pretreated with silane coupling agent. The results showed that the yield stress (σ_y) decreased gently for PP/TK70 systems, whereas decreased relatively obviously for PP/TK35 systems with increasing the volume fraction (?_f) of the fillers. When ?_f was less than 5%, the tensile strength at break (σ_b) of the composites increased with the increase of ?_f. When ?_f was more than 5%, σ_b was almost a constant for PP/TK70 systems, while σ_b decreased linearly for PP/TK35 systems. The tensile fracture strain (ε_b) of the composites decreased suddenly when ?_f was less than 5%, and then decreased slightly with increasing ?_f. When ?_f was 10%, σ_y and σ_b increased while ε_b decreased with the increase of the bead diameter. Furthermore, the σ_y was predicted by means an equation proposed in the previous work, and good interfacial adhesion was shown between the hollow glass beads and the matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1697–1701, 2007     

Crystallization behavior of glass bead‐filled low‐density polyethylene composites

The effects of the filler content and the filler size on the crystallization and melting behavior of glass bead‐filled low‐density polyethylene (LDPE) composites have been studied by means of a differential scanning calorimeter (DSC). It is found that the values of melting enthalpy (ΔH_c) and degree of crystallinity (x_c) of the composites increase nonlinearly with increasing the volume fraction of glass beads, ϕ_f, when ϕ_f is greater than 5%; the crystallization temperatures (T_c) and the melting temperatures (T_m) of the composites are slightly higher than those of the pure LDPE; the effects of glass bead size on x_c, T_c, and T_m are insignificant at lower filler content; but the x_c for the LDPE filled with smaller glass beads is obviously greater than that of the filled system with bigger ones at higher ϕ_f. It suggests that small particles are more beneficial to increase in crystallinity of the composites than big ones, especially at higher filler content. In addition, the influence of the filler surface pretreated with a silane coupling agent on the crystallization behavior are not too outstanding at lower inclusion concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 687–692, 1999     

Effects of glass bead content and surface treatment on viscoelasticity of filled polypropylene/elastomer hybrid composites

The dynamic mechanical properties of A‐glass bead filled polypropylene (PP)/ethylene–propylene–diene monomers polymer (EPDM) ternary composites have been measured over a temperature range from −80 °C to 100 °C and at a fixed frequency of 1 Hz, using a dynamic mechanical analyser (DMA), to identify the effects of the filler content and its surface treatment with a silane coupling agent on the dynamic viscoelastic behaviour. The results show that the storage modulus (E′_c) and loss modulus (E ″_c) of these composites with 10% volume fraction of EPDM at 25 °C increase non‐linearly with increasing volume fraction of glass beads (ϕ_g). At the same test conditions, the E′_c value of the PP/EPDM filled with pretreated glass beads is higher than that of the uncoated glass bead filled PP/EPDM system, especially at higher ϕ_g, while the difference in E ″_c between both systems is very small. The mechanical damping for the former decreases with increasing ϕ_g, but the opposite is true for the latter. The glass transition temperature of these composites varies irregularly with ϕ_g. The dynamic complex viscosity increases nonlinearly with an increase of ϕ_g. In addition, the interfacial structure between the matrix and inclusions has been observed by means of a scanning electron microscope. © 1999 Society of Chemical Industry     

Tensile and Impact Properties of Hollow Glass Bead‐Filled PVC Composites

The tensile and notched Izod impact properties of poly(vinyl chloride) (PVC) composites filled with hollow glass beads (HGB) were measured at room temperature by means of an Instron materials testing machine to investigate the effects of the filler content and size on these mechanical properties. The results showed that the tensile yield strength (σ_yc) decreased gently with increasing HGB volume fraction (ϕ _f), while the tensile break strength (σ_bc) of the composites was somewhat greater than that of the unfilled PVC within ϕ _f = 0–20%. In addition, the dependence of σ_bc on ϕ _f was not obvious. The effect of HGB size on both σ_yc and σ_bc was insignificant. When ϕ _f < 5%, the notched impact strength (σ_IC) of the composites decreased quickly with increasing ϕ _f, and then it decreased slightly with the increase of ϕ _f. Similarly, the influence of the filler size on the impact properties was insignificant. Furthermore, the σ_yc of the samples was estimated using a tensile equation proposed in a previous paper. A good agreement was shown between the calculations and the measured data.     

Hybrid‐filler filled polypropylene/(natural rubber) composites: Effects of natural weathering on mechanical and thermal properties and morphology

Comparison was made between the properties of recycled newspaper (RNP)/carbon black (CB) and recycled newspaper (RNP)/silica hybrid filled polypropylene (PP)/natural rubber (NR) composites. The properties studied were mechanical, thermal, and morphological. These composites were also subjected to natural weathering, i.e., the tropical climate in Penang, Malaysia, for 6 months. The incorporation of CB and silica at all weight ratios of RNP/CB and RNP/silica hybrid gave increases in tensile strength, elongation at break (E_B), Young's modulus, melting temperature (T_m), heat of fusion of composites (ΔH_f(com)), crystallinity of composites (X_com), and the crystallinity of PP (X_PP). As expected, the tensile properties (except for Young's modulus), T_m, ΔH_f(com), X_com, and X_PP of the composites exhibited lower values after weathering than before weathering. The extent of chemical degradation was studied by Fourier transform infrared spectroscopy, and the results showed the formation of several functional groups, i.e., hydroxyl, hydroperoxide, vinyl, carboxylic acid, and ketone. At the same filler weight ratio, the composites filled with RNP/CB hybrid showed higher values of tensile strength and E_B but lower values of Young's modulus, ΔH_f(com), X_PP, and X_PP, as compared to those with the RNP/silica hybrid under weathering conditions. The good retention in tensile properties indicated that the replacement of RNP by CB and silica improved the weatherability performance of the PP/NR composites. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers     

Tensile properties and damage behaviors of glass‐bead‐filled modified polyphenylene oxide under large strain

Based on Continuum Damage Mechanics (CDM), a damage model for glass‐bead‐filled modified polyphenylene oxide (GB/PPO) has been proposed to describe its damage behavior at various levels of tensile strain by considering the reduction of effective loading area. Hence, an equation for prediction of effective elastic modulus of the damaged GB/PPO composites in terms of the three principal true strains was derived. The tensile properties and damage behaviors of the GB/PPO composites with different volume percentages of glass beads were investigated using standard tensile tests and load‐unload tests, respectively. The addition of glass beads increases Young's modulus of PPO but has a weakening effect on its tensile strength. A maximum value of tensile work to break and tensile strain at break was found when 5 vol% of glass beads with a mean diameter of 11 μm was blended with PPO. These results were justified through microscopic examination of the fracture surfaces of the tensile specimens by using a scanning electron microscope (SEM). In‐situ observations of the strain damage processes were made through the SEM equipped with a tensile stage to determine the strain at fully debonding of glass beads. The volumetric strain of GB/PPO composites increases because of microcavitation during strain damage. In general, the prediction for the effective elastic modulus of the damaged GB/PPO composites at different true strains is slightly higher than the experimental results. The damage evolution rates after fully debonding of glass beads from the matrix are close to those predicted by the proposed damage model.     

Temperature dependence of the tensile strength of glass fiber–epoxy and glass fiber–unsaturated polyester composites

Epoxy and unsaturated polyester resins reinforced with random-planar orientation of short glass fibers were prepared and the temperature dependence of their tensile strength was studied. The tensile strength decreases as the temperature increases, and this tendency can be expressed in terms of critical fiber length l_c and apparent interfacial shear strength τ: where σ_cs is the tensile strength of composite reinforced with random-planar orientation of short fibers, L is the fiber length, d is the fiber diameter, σ_f is the tensile strength of fiber, σ_m is the tensile strength of matrix, u_f is the volume fraction of fiber, v_m is the volume fraction of matrix, and σ′_m is the stress of the matrix at fracture strain of the composite. The experimental strength values at room temperature are considerably smaller than the theoretical values, and this difference can be explained by the thermal stress produced during molding due to the large difference in the thermal expansion coefficient between glass fiber and matrix resin.     

Polymer whiskers of poly(4-hydroxybenzoate): Reinforcement efficiency in composites with polyamides

The reinforcing efficiency of polymer whiskers of poly(4-hydroxybenzoate) (PHB) in poly-amide-6 (PA-6) and polyamide-11 (PA-11) composites was investigated by tensile testing, scanning electron microscopy (SEM), and density measurements. The composites were prepared by mixing the whiskers into the melts of the polyamides. Ductile and stiff PA-6-composites with different crystallinities of the PA-6-matrix were investigated. In the ductile PA-6 (low crystallinity) composites, the elastic modulus E and the yield stress σ_f increase more than twice at a whisker content of 2 vol %. The increase in E and σ_f in stiff PA-6 (high crystallinity) composites is not as pronounced as in the ductile PA-6 composites, but is still remarkably higher than in the PA-11 composites, which is about 1.2 times at a whisker content of 2 vol %. At higher whisker content, the PA-6 composites show the opposite of the PA-11-composite—no further increase in E and σ_f, which may be due to an agglomoration of whiskers in the high viscous PA-6 melt. The different tensile properties of the composites can be explained by SEM analysis of the fracture surfaces, which shows that the adhesion of PA-6 to the PHB whiskers is better than of PA-11. This is due to a higher number of hydrogen bonds between the PA-6 and the whisker surface. Density measurements show that the crystallinity of the polyamides is not affected by the PHB whiskers. © 1996 John Wiley & Sons, Inc.     

Structure of the epoxy–chelate metal-containing matrices: Theoretical aspects

A theoretical analysis has been carried out of the structure of metalliferous epoxy–chelate polymers (MECP) based on diglycidyl ether of bisphenol-A (DGEBA) hardened with metal complexes of the formula [M(L)_n(X)_p], where M is the cation of the transition metal; R, a nitrogen-containing ligand; X, the anion of an organic acid; n, the number of the ligands in the complex molecule (n = 1 or 2), and p, the metal valency (p = 2 or 3). On the basis of the correlations between the tensile strength (σ_t) and tensile modulus (E_t), and flexural strength (σ_f) and flexural modulus (E_f), of MECP, σ_t = f(E_t)and σ_f = f(E_f), and supposing that when the condition $ \sigma _{_{t_A } }= \sigma _{_{t_B } } ,{\rm}\sigma _{_{f_A } }= \sigma _{f_B } ,{\rm}E_{t_A }= E_{t_B } ,{\rm}E_{f_A }= E_{f_B } $ is fulfilled, where A and B are complex hardeners of different structures but of the same class, the epoxy–chelate matrices have similar structures. The influence of the structural fragments of the hardener molecule (the metal, ligand, and anion) on the polymer properties was evaluated and it was found out that the biggest contribution to these properties belongs to the metal, the alteration of which changes the thermal stability (ΔM is the polymer mass loss after thermal treatment in air), deformability (ε), σ_f, E_f, and deflection temperature (DT) significantly. By this, the effect of the hardener structure change on the alteration of the MECP properties is maximal for ΔM, is minimal for the compressive strength (σ_c), and decreases in the series: ΔM > ε > DT > σ_f > E_f > σ_c. The type of the anion affects σ_c significantly, but the ligand type contributes the least to the polymer properties. The obtained dependencies of the MECP properties on the structural fragments of the complex hardeners allow preliminary evaluation of the structure of the chelates and epoxy–chelate compositions necessary to produce epoxy polymers with required properties. The new method of the theoretical investigation of the effect of the structural fragments (method of TIESF) of the polymer matrix on the polymer properties can be used to analyze the structures of the polymers of other classes and to predict the optimal structures, promising the production of the materials with the optimal properties. © 1993 John Wiley & Sons, Inc.     

Mechanical and thermal properties of chitosan‐filled polypropylene composites: The effect of acrylic acid

The mechanical properties, morphology, and thermal properties of chitosan‐filled polypropylene (PP) composites have been studied. The effect of the chemical modification of chitosan by acrylic acid treatment was also investigated. Results showed that the tensile strength and elongation at break decreased but that the Young's modulus of the composites increased with increasing filler loading. Chemical modification of chitosan with acrylic acid improved the tensile strength and Young's modulus of the composites but reduced the elongation at break. Thermogravimetric analysis showed that the addition of chitosan improved the thermal stability of the PP/chitosan composites as compared to that of neat PP. Chemical modification of chitosan had a positive effect on the thermal stability of the composites. This change was attributed to improvement of the interfacial adhesion between the chitosan and PP matrix due to formation of a covalent bond between chitosan and acrylic acid. Meanwhile, differential scanning calorimetric analysis showed that the addition of filler did not significantly change the melting temperature (T_m) of the PP/chitosan composites. The degree of crystallinity of the composites decreased with the addition of chitosan. At a similar chitosan loading, the chemically treated PP/chitosan composites exhibited higher crystallinity than the untreated composites and exhibited slightly increased T_m. A scanning electron microscopy study of the tensile fracture surface of chemically treated PP/chitosan composites indicated that the presence of acrylic acid increased the interfacial interaction between chitosan and the polypropylene matrix. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Mechanical Properties of PPS/PC/GF/Nano-CaCO3 Hybrid Composites

A kind of nanometer calcium carbonate (nano-CaCO₃) filled glass fibre-reinforced polyphenylene sulfide/polycarbonate (PPS/PC/GF) hybrid composites were fabricated with a twin-screw extruder in this paper, and the surface of the nanometer particles was pretreated with stearic acid in a high speed mixer before melt blending. The Young's modulus, tensile strength, tensile elongation at break, flexural modulus and strength of these hybrid composites were measured at room temperature by using a universal materials testing machine, to identify the influence of the nano-CaCO₃ content on the mechanical properties of these hybrid composites. It was found that there were relatively evident reinforcing and toughening effects of the nano-CaCO₃ on the PPS/PC/GF hybrid composites. The Young's modulus, tensile strength, flexural strengt and elongation at break of these composites increased nonlinearly with an addition of the nano-CaCO₃ weigh fraction (φ _f ) when φ _f was less than 6%, and they reached the maximum at φ _f of 6%, and then decreased; while the flexural modulus increased as φ _f was less than 4%, and then decreased.     

Impact fracture toughness and morphology of diatomite‐filled polypropylene composites

Impact fracture strength is an important characterization for impact toughness of materials. A polypropylene (PP) filled with diatomite with different diameter (5, 7, and 13 μm) was fabricated by means a twin‐screw extruder. The impact fracture strength of these composites was measured at room temperature to identify the effects of diatomite content and diameter on impact fracture strength of filled polypropylene composites. The results showed that the influence of diatomite on the notched impact strength was significant. When the volume fraction of the diatomite (?_f) was less than 10%, the notched impact strength (σ_I) increased quickly with an addition of ?_f, and then the variation of σ_I was slight. The notched impact strength of the composite with the diatomite diameter of 7 μm is the highest when ?_f was 10%. Furthermore, the impact fracture surface was observed by using a scanning electronic microscope (SEM) to study the toughening mechanisms. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Stiffness and toughness of polypropylene/glass bead composites

The effects of coupling effect, particle diameter (d), volume fraction (V_b) and size distribution (σ) of glass beads on the impact strength and tensile modulus of polypropylene (PP)/glass bead composites have been investigated. The toughness and stiffness of the composite can be simultanously enhanced by using a titanate coupling agent, which gives rise to a moderate interfacial adhesion (characterized by an interaction parameter B ∼ 1) between the glass beads and the matrix. With the addition of this coupling agent, the impact strength of the PP/glass bead composite with d = 2.7 μm and σ = 1.85 increases about 4.5 times as V_b increases from 0 to 0.25, while the tensile modulus remains roughly unchanged. For the composites with larger d and narrower size distribution, the impact strength increases only slightly with increasing V_b. The combined effect of d, V_b and size distribution of the glass beads are described by using a single parameter, the average matrix ligament thickness T . Unlike rubber‐modified polymers, the impact strength of PP/glass bead composites does not follow a master curve when plotted against T .     

Mechanical properties and morphologies of PP/mPE/filler composites

Because of the poor impact behavior of polypropylene (PP) at low temperatures, the blending of PP with metallocene‐polymerized polyethylene (mPE) elastomers was investigated in this study. However, a reduced modulus of the overall blend was inevitable because of the addition to elastomers. To obtain a balance of the properties, we introduced rigid inorganic fillers to PP/mPE blends. The performance of the composites was characterized with tensile and Charpy notched impact tests, and the fracture morphology was examined with scanning electron microscopy. The results showed that the effects of fillers in a brittle matrix and in a ductile matrix were quantitatively different. For PP/mPE/filler ternary composites, the dependence of Young's modulus and yield strength on CaCO₃ content was not significant compared with that of PP/filler binary composites, whereas the elongation at break and tensile toughness at room temperature for PP/mPE/filler systems were more improved. The impact strength of the PP/mPE blends filled with untreated glass beads and CaCO₃ at a low temperature was lowered because of the weak interfacial bond. However, the values of the impact strength of the PP/mPE/filler composites at a low temperature remained at a high level compared with that of pure PP. In particular, a PP/mPE blend filled with surface‐treated kaolin had a higher low‐temperature impact toughness than the unfilled blend. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3029–3035, 2002; DOI 10.1002/app.2333     

Multiwalled carbon nanotubes‐based polypropylene composites: Influence of interfacial interaction on the crystallization behavior of polypropylene

Composites of polypropylene (PP) and multi‐walled carbon nanotubes (MWCNTs) were prepared via melt‐mixing utilizing Li‐salt of 6‐amino heaxanoic acid (Li‐AHA) modified MWCNTs in the presence of a compatibilizer (polypropylene‐g‐maleic anhydride; PP‐g‐MA). Improved interaction between the anhydride group of PP‐g‐MA and the amine functionality of Li‐AHA was confirmed via FTIR and Raman spectroscopic analysis. A higher glass transition temperature (T_g) of the PP phase has been observed in these composites as compared to pristine MWCNTs‐based composites. The crystallization temperature (T_c) of the PP phase was increased as a function of pristine MWCNTs concentration in PP/MWCNTs composites indicating hetero‐nucleating action of MWCNTs. However, T_c value was decreased in the presence of Li‐AHA modified MWCNTs indicating the adsorbed Li‐AHA on the MWCNTs surface. Moreover, T_c value was higher in the presence of Li‐AHA modified MWCNTs with PP‐g‐MA as compared to that of without PP‐g‐MA, suggesting the desorbed Li‐AHA from the MWCNTs surface due to melt‐interfacial reaction. Further, MWCNTs were extracted by hot vacuum filtration technique from PP/MWCNTs composites containing Li‐AHA and PP‐g‐MA. The isothermal crystallization kinetics showed a variation in crystallization behavior of the PP phase in the corresponding composites as compared to the “extracted MWCNTs.” POLYM. ENG. SCI., 57:183–196, 2017. © 2016 Society of Plastics Engineers     

Preparation and properties of polyamide‐6‐based thermoplastic laminate composites by a novel in‐mold polymerization technique

In this work, a method for preparation of polyamide‐6 (PA6) based laminates reinforced by glass fiber‐ (GFL) or polyamide‐66 (PA66) textile structures (PL) via reactive injection molding is disclosed. It is based on in‐mold anionic polymerization of ε‐caprolactam carried out at 165°C in the presence of the respective reinforcements performed in newly developed prototype equipment whose design concept and operation are described. Both composite types were produced for reaction times of 20 min, with conversion degrees of 97–99%. Initial mechanical tests in tension of GFL samples displayed almost twofold increase of the Young's modulus and stress at break values when compared with the neat anionic PA6. The improvement was proportional to the volume fraction V_f of glass fiber fabric that was varied in the 0.16–0.25 range. A 300% growth of the impact strength was registered in PL composites with V_f of PA66 textile of 0.1. Removing the surface finish of the latter was found to be a factor for improving the adhesion at the matrix–fiber interface. The mechanical behavior of GFL and PL composites was discussed in conjunction with the morphology of the samples studied by optical and electron microscopy and the matrix crystalline structure as revealed by synchrotron X‐ray diffraction. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40083.     

Optomechanical variations in cold‐drawn thermally treated polypropylene fibers

A two‐beam polarizing interference microscope with a microstrain device was used for measuring some optical and mechanical parameters for polypropylene (PP) fibers at room temperature (28 ± 1°C). The changes in the molecular orientation were evaluated to obtain orientation factors f₂(θ), f₄(θ), f₆(θ), 〈P₂(cos θ)〉, 〈P₄(cos θ)〉, and crystalline and amorphous orientation functions F_c and F_a, respectively. The shrinkage factor, uniaxial tension, true stress, molar refractivity R, surface reflectivity R′, the crosslink density N_s, the chain entanglement density N_c, the segment anisotropy γ_s, and the number of chains N′ were calculated. In addition, the shrinkage stress was found to increase with the increase of draw ratio. The dielectric constant ε, the dielectric susceptibility η, the average work per chain w′, and the constants of the stress–birefringence equation were obtained. Comparison between Hermans's optical orientation functions and the corrected formulas by de Vries are given. The values of fully oriented refractive indices n₁ and n₂ were found. The generalized Lorentz–Lorenz equation given by de Vries was used to determine the structural parameters of PP fibers. An empirical formula was suggested to correlate the changes in the evaluated parameters with different draw ratios, and its constants were determined. The study demonstrated changes on the molecular orientation factors and evaluated microstructural parameters as a result of an applied cold‐drawing process. Relationships between the calculated parameters and the draw ratios, together with microinterferograms were presented for illustration. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 729–738, 2003     

Preparation and properties of aluminum nitride‐filled epoxy composites: Effect of filler characteristics and composite processing conditions

Polymer‐matrix composites based on brominated epoxy as the matrix and aluminum nitride (AlN) particle as the filler were prepared. Effects of AlN size and content as well as composite processing conditions on the preparation and properties of the composites had been investigated. At the same processing conditions, Young's modulus (E) and dielectric constant (D_k) of the composites increase, whereas coefficient of thermal expansion decreases when increasing AlN content or decreasing AlN size; tensile strength and elongation at break first increase then decrease with AlN content, and they reach maximum values at lower AlN content with decreasing AlN size; glass transition temperature (T_g) also exhibits a trend of first increase then decrease with AlN content, and it decreases with decreasing AlN size, especially at high AlN content; dissipation factor (D_f) generally decreases with AlN content except for the composites filled with 50 nm‐AlN, and it increases with decreasing AlN size. Comparing the composites prepared at different processing conditions, the properties of the composite are relatively poor at low vacuum conditions during removal of solvent and bubble. The scanning electron microscope and Fourier transform infrared analyses indicate that the properties of the composites are related to the aggregation of AlN filler and voids in the composites as well as the crosslink density of epoxy matrix. The preparation of the composites is also found to be affected by AlN size and content as well as vacuum conditions, indicating that increase of viscosity of system and/or the solvent evaporation during curing results in poor formability of the composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013