Structure and properties of polyimide‐bonded magnets processed from prepolymers based on diacetyl derivatives of aromatic diamines and dianhydrides

We report a novel method of polyimide (PI) synthesis from prepolymers based on dianhydrides and diacetyl derivatives of aromatic diamines that facilitate the preparation of a melt processable mixture at 300 ± 10°C of the prepolymer and magnetic Nd‐Fe‐B alloy to provide PI‐bonded magnets with enhanced properties. It is shown that chemical structure of the prepolymers strongly influences viscosity behavior via crystallization of the oligoimide in the melt, leading to formation of PI with rigid‐rod like structure. This structural ordering of the prepolymers based on diacetyl derivative of diamine used in this study, if not controlled, leads to exponential increase of melt viscosity with time, making it practically impossible to prepare melt processable mixture of the magnetic particles and the PI prepolymers at elevated temperatures. The results obtained demonstrate that appropriate dianhydrides and diacetyl derivatives of diamines that do not lead to crystallization of oligoimides in prepolymer mixture can be used under controlled processing conditions to prepare melt‐processable PI‐bonded magnets containing rigid‐rod like PI structure that significantly increases thermal stability of the magnets. The temperature dependencies of the magnetic properties of the PI‐bonded magnets under conditions that they are likely to encounter during their service life were found to be remarkably similar to that of commercial thermoplastic magnets such as injection‐molded nylon magnets. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 478–485, 2006     

Effect of coupling agent and filler particle size on melt rheology of polymer-bonded Nd-Fe-B magnets

The effect of coupling agents and filler particle size on melt rheology of poly(phenylene sulfide)-bonded neodymium-iron-boron (Nd-Fe-B) alloy magnets was studied with oscillatory flow experiments to accelerate efforts to optimize their processing. The minimum viscosity of the polymer-bonded magnets near 290°C was obtained with Nd Fe B fillers (106–150 particle size range) that were coupled with a silane coupling agent. All the samples tested followed power-law fluid flow behavior. Morphological and dynamic mechanical analysis of the samples showed that the beneficial function of the coupling agent may be ascribed to enhanced wetting of the magnetic Nd Fe B powders by the polymer, improving the processability of the polymer bonded magnets.     

An electrodeposition metal layers method for magnetic powders and warm-pressing preparation of Nd–Fe–B/Sn-bonded magnets

The method of magnetic stirring in fluid-bed galvanic deposits was used for cladding low-melting-point metallic tins onto the surface of rapid quenching Nd–Fe–B magnetic powders. This form of bonding was also used to make Nd–Fe–B/Sn composite magnets by warm pressing at 300 °C. The tin-plating layers of the Nd–Fe–B magnetic particles were observed by scanning electron microscope (SEM). The magnetic properties of the coated and uncoated powders were examined by vibrating sample magnetometer (VSM), respectively. Furthermore, both the compressive strength and magnetic properties of Sn-coated Nd–Fe–B/Sn-bonded magnets were measured. The results indicate that not only the tin plated and magnetic powders were bonded closely, but also the content of tin-plated layers can be controlled by the electrical current. The (BH)_max and B_r value of magnetic powders decrease with the increasing content of plated tin. An increase in the tin-plated content results in an elevation in magnetic properties of composite magnets by warm-pressing preparation. The composite magnets exhibit excellent integrated magnetic property when the content of Sn was 5.079 wt.%, at (BH)_max = 113.7 kJ m^?3, B_r = 0.821 T, H_cj = 732.6 kA m^?1. The results indicate that the required electrodeposited tin is less than 5 wt.% achieving the same magnetic properties and compressive strength which demands 10 wt.% tin in mechanical mixing method.     

Effects on the melt rheology of systems of Nd‐Fe‐B particles suspended in a poly(phenylene sulfide) and liquid crystalline polymer blend

The melt rheology of blends of a liquid crystalline polymer (LCP) and poly(phenylene sulfide) (PPS) and their composites with ferromagnetic Nd‐Fe‐B particles (MQP) was studied. We investigated the effects of LCP concentration, Nd‐Fe‐B particle volume fraction and size, distribution, and shear rate on the rheological properties of these composites. Enthalpy of fusion changes that were observed resulted from the addition of the LCP and Nd‐Fe‐B particles to the polymer blends/composites. The shear rate and frequency dependencies of the materials revealed a viscosity reduction at low (1–3 wt%) and moderate (10–15 wt%) LCP concentrations, and strong effects on the shear‐thinning characteristics of the melt. The suspensions of polydispersed Nd‐Fe‐B particle configurations in PPS that were of lower size ratios gave better processability, which is contradictory to previously reported behavior of suspensions containing spherical particles. Specifically, the compositions with unimodal and a bimodal distribution of Nd‐Fe‐B particles gave the lowest viscosities. The experimental data were correlated with semi‐empirical viscosity model equations of Maron‐Pierce, Krieger‐Dougherty, Eilers, and Thomas and were found to be consistent with the data. The maximum packing fraction, ϕ_m, of the MQP particles was estimated to be within the range of 0.78 ϕ ≤_m ≤ 1.0 through graphical and parametric evaluation methods.     

Tensile and heat resistance behavior of modified thermoplastic polyurethane elastomer in anisotropic neodymium-iron-born bonded magnet

The emergence of anisotropic neodymium-iron-boron (NdFeB)-bonded magnets with high energy density and freedom of shape design is effective in minimizing the dimensions and mass of electric motors. However, limitations in mechanical strength and heat resistance at elevated temperatures hinder their further application. To overcome these challenges, we present a novel approach to enhance the tensile strength and heat resistance of the NdFeB-bonded magnet involving the modification of thermoplastic polyurethane (TPU) through the melt-mixing method with a styrene–acrylonitrile-glycidyl methacrylate terpolymer (SAG) modifier and engineered TPU was then employed in fabricating NdFeB-bonded magnets via calendering molding. The microstructure of the magnets exhibited aligned NdFeB particles due to mechanical stress during calendering molding, which results in anisotropy. Interestingly, the magnetic properties of bonded magnets based on modified TPU remain almost the same compared to their unmodified counterparts, showcasing a maximum energy product of around 12 MGOe. The mechanical tests demonstrated a maximum 32.4% increase in the tensile strength of bonded magnets based on modified TPU. A progressive shift to a higher temperature (100 to 120°C) of magnet samples fractured occurs in the heat resistance measurement of the bonded magnets based on modified TPU, meaning improvement in heat resistance of NdFeB bonded magnets.     

钕铁硼磁性塑料及其注射成型的研究

通过对快淬钕铁硼(NdFeB)磁粉进行包覆，并用硅烷偶联剂KH550进行表面处理，以PA12做粘结剂，添加复配润滑剂及抗氧剂，在保证磁性能即高磁粉含量(91％)的条件下，很好地解决了NdFeB塑料粘结磁体流动性差及磁体在湿热环境下易氧化生锈的问题。并研究了注射成型NdFeB塑料粘结磁体的制备工艺、磁粉表面处理、磁粉含量、添加剂等因素对磁性能、加工性能、力学性能的影响。     

Polyimide bonded magnets: Processing and properties

We report a new method of polyimide synthesis based on the interaction of dianhydrides with acylated diamines for preparing a melt processable mixture of prepolymer and rare earth magnetic alloy particles in the form of 75–100 μm particles. This mixture can be easily converted to useful thermoplastic polyimide bonded magnets by heating at 300°C. It is shown that the prepolymer based on 1,3‐bis(3,4‐dicarboxyphenoxy)benzene dianhydride and the diacetyl derivative of 2,2‐bis(4‐(4‐aminophenoxy)phenyl)sulfone diamine after removing less than 5% by weight of the volatile components can be melted at 220–240°C to give a fluid with a viscosity of 10–20 Pas. This low viscosity of the prepolymer facilitates blending it with magnetic particles at relatively high volume fractions (up to 85 vol %) that are not possible using conventional methods. The resulting polyimide‐bonded magnets exhibit excellent thermal stability and a high storage modulus of 10 GPa at 400°C. Magnetic property measurements showed a ≥10% increase in energy products over that of typical commercial bonded magnet materials such as the ones containing thermoplastic poly(phenylene sulfide) or polyamide matrices. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3151–3158, 2003     

Mechanical and morphological study of polyphenylene sulfide/liquid crystalline polymer blends compatibilized with a maleic anhydride grafted copolymer

Blends of thermotropic liquid crystalline polymer (LCPA‐950), based on a copolyester of hydroxynapthoic acid and hydroxybenzoic acid with an engineering thermoplastic, poly(phenylene sulfide) (PPS), were prepared using a corotating twin‐screw extruder. Addition of a third component, a functionalized polypropylene (maleic anhydride grafted polypropylene, MA‐PP), that interact with the thermotropic liquid crystalline polymer (TLCP) facilitates the structural development of the TLCP phase by acting as a compatibilizer at the interface. Differential scanning calorimetry and dynamic mechanical thermal analysis results, however, show that there is an interaction between the polymers in the presence of compatibilizer. This means that MA‐PP can be used as a compatibilizer for the PPS/LCP in situ composite system. The viscosity of the compatibilized in situ composite was decreased by the compatibilizer, and this is mainly due to the fibrous structure of the LCP at the high shear rate. The mechanical properties of the ternary blends were increased when a proper amount of MA‐PP was added. This is attributed to fine fibril generation induced by the addition of MA‐PP. Morphological observations determined the significance of the third component in immiscible polymer blends, and an optimum amount of MA‐PP exists for the best mechanical performance. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of a Nd—Fe—B magnetic filler on the crystallization of poly(phenylene sulfide)

The crystallization of poly(phenylene sulfide) (PPS) in a polymer–magnetic Nd—Fe—B powder suspension was studied. Isothermal crystallization behavior was analyzed by way of differential scanning calorimetry, and the kinetics were described via the Avrami equation. The Avrami parameters and the crystallization times were strongly affected by both the particle size and the presence of a coupling agent coated on the filler particles. The small Nd—Fe—B particles exhibited long induction and half‐times, whereas the large particles tended to have short crystallization times. Particles ranging from 38 to 150 μ appeared to have similar crystallization times and to have no significant change in the value of Avrami index with melt crystallization temperature. As a result of these analyses, the dynamic mechanical properties were determined to correlate the fundamental polymer crystallization characteristics and the physical properties of the PPS binder. The enhancement of the wetting of the filler to the binder was promoted through the coupling agent, as confirmed by dynamic mechanical testing performed on the samples. The storage modulus typically decreased because of the presence of the uncoated small particles. Conversely, the loss modulus was enhanced because of the presence of the coated small particles in the PPS binder. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1091–1102, 2002     

Poly(p-phenylene sulfide)/liquid crystalline polymer blends. II. Crystallization kinetics

The crystallization kinetics of blends made of poly(p-phenylene sulfide) (PPS) with a liquid crystalline polymer (LCP) was studied. The blends were found to be immiscible by dynamic mechanical thermal analysis (DMTA). Results of non-isothermal and isothermal crystallization experiments made by differential scanning calorimetry (DSC) showed that both components had their crystallization temperatures increased; also the LCP melting temperature was found to increase in the blends. It was concluded that the addition of LCP to the PPS increased the PPS overall crystallization rate due to heterogeneous nucleation. The fold interfacial free energy, σ_e of the PPS in the blends was observed not to vary with composition. © 1996 John Wiley & Sons, Inc.     

Dispersion of Poly(phenylene ether) in a Poly(phenylene sulfide)/Poly(phenylene ether) Alloy

We have devised and developed a new method for the preparation of a poly(phenylene sulfide)/poly(phenylene ether) (PPS/PPE) alloy, which has micro‐dispersed PPE in the PPS matrix. PPS was chemically treated to activate the reactivity of the PPS end‐group by extrusion in the presence of diphenylmethane diisocyanate (MDI) in its molten state at 300°C. The reactive processing of the MDI‐treated PPS with maleic anhydride‐modified PPE gave a PPS/PPE alloy with micro‐dispersed PPE in the PPS matrix. The PPS/PPE alloy showed mechanical properties superior to those of PPS at elevated temperature (150°C) and also showed precision‐molding ability superior to that of PPS.     

Blends of a thermotropic LCP and a thermoplastic elastomer. II: Formation and stability of LCP fibers

The formation of fibers during blending of a thermotropic liquid crystalline polymer (LCP) with a thermoplastic elastomer (TPE) using shear flow, and the stability of the fibers and the blend morphologies at elevated temperatures were studied. The polymers used were Vectra A900 (LCP) and Kraton G1650 (TPE). Fiber formation in (predominantly) shear flow was studied using a single screw extruder of which the die was removed. Fibers were obtained in blends with 5 vol% LCP at shear rates as low as 6.3 s^?1. Conventional extrusion through a die was used for preparing materials for the studies of the thermal stability of blends and isolated fibers–isolated LCP-fibers surrounded by a TPE-matrix disintegrate when held above the melting point of the LCP. Annealing of the blends at this melting temperature results in changes of the morphology and in a fairly rapid decrease of the modulus of elasticity.     

纳米晶NdFeB永磁粉的吸氢研究

研究了纳米晶NdFeB永磁粉在0.1 MPa氢压,不同温度下的吸氢规律;并分别对晶化后、氢化后以及歧化后的纳米晶NdFeB永磁粉进行球磨处理。结果表明,纳米晶NdFeB永磁粉在250℃下才开始吸氢,保温3 h达到最大吸氢量Nd2Fe14BH3.31;随着温度升高,吸氢量并没有增加;当温度升高到450℃时,开始歧化反应;球磨5 h后,氢化粉最为细小均匀,而歧化粉则最为粗大。     

Poly(p-phenylene sulphide)/liquid crystalline polymer blends. I. Miscibility and morphologic studies

The miscibility in the melt and solid state of blends made of poly(p-phenylene sulphide) (PPS) with a liquid crystalline polymer (LCP) from DuPont was studied by polarized light optical microscopy (PLOM) and dynamic thermal mechanical analysis. Both techniques showed that the PPS and the LCP are immiscible in both states, and that the critical concentration for the formation of fibrils C^*, in this particular system, was located between 20 and 25 wt % LCP. The resultant blend morphology was studied by PLOM and scanning electron microscopy (SEM). It was observed that when LCP fibrils are formed in the PPS matrix, the PPS macromolecules will crystallize around the LCP fibrils by forming columnar layers called transcrystallites. These transcrystallites are the result of the LCP acting as a nucleating agent for the PPS, promoting heterogeneous nucleation. © 1996 John Wiley & Sons, Inc.     

Blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer. I: Mechanical properties and morphology

Blends of a thermotropic liquid crystalline polymer (LCP), Vectra A900, and a thermoplastic elastomer, Kraton G1650, were made on a single screw extruder. During extrusion, fibers of the LCP are formed under influence of shearing and elongating forces. The stiffness and tensile strength of the elastomer are greatly improved by the addition of the LCP. The modulus of elasticity of blends containing up to 20% LCP can be described well with the Halpin-Tsai equation. Differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA) measurements show that the polymers are immiscible, but the DMTA results show a shift of the glass transition temperature of the elastomeric block of the Kraton polymer. This shift may be attributed to a layer of elastomer adsorbed on the LCP particles.     

Thermo‐mechanical behavior of stretch‐broken carbon fiber and thermoplastic resin composites during manufacturing

Stretch‐broken fiber reinforcements and thermoplastic resin commingled prepregs are interesting for manufacturing composite parts in aeronautic and automobile industries. With these materials it is possible to produce composite parts with complex geometries, and high curvatures. On the other hand the length of the fibers leads to mechanical properties of the final composite that are close to those of the composite with continuous fibers. This paper analyzes the thermo‐mechanical properties of Stretch Broken Carbon Fiber (SBCF) / PPS and PEEK commingled prepregs during manufacturing. Tensile and in‐plane shear tests at different temperatures are analyzed. The experiments are realized in an isothermal oven. The range of temperature is those of the part during a thermoforming process. The experimental data allow to analyze the differences on the tensile and in‐plane shear behaviors at different temperatures between thermoplastic prepregs with continuous fibers and thermoplastic prepregs with stretch‐broken fibers. Forming simulations show that wrinkling can be avoided with SBCF prepregs while these wrinkles develop during continuous fibers prepreg forming. POLYM. COMPOS., 36:694–703, 2015. © 2014 Society of Plastics Engineers     

Synthesis and properties of magnets/polyethylene composites

Polyethylene‐based magnetic composites have been prepared by ethylene polymerization on the surface of NdFeB magnets, which is previously activated by ball milling with catalyst components. The level of magnets has been controlled by catalyst preparation and polymerization parameters such as Al/Ti ratio and polymerization temperature. The coertivity and the residual magnetizability were investigated. It was found that the magnetic properties of magnet powders are largely retained. In addition, in contrast to composites prepared by melt mixing, the adhesion force between magnets and polymer matrix is improved significantly and better mechanical properties are expected. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3412–3416, 1999     

注射成型钕铁硼塑料粘结磁体的研究

对快淬钕铁硼(NdFeB)磁粉进行包覆，并用硅烷偶联剂KH550进行表面处理，以尼龙12作粘结剂．添加复配润滑剂及抗氧剂，在保证磁性能即高磁粉含量(91％)的条件下，很好地解决了复合体系流动性差及磁体在湿热环境下易氧化生锈的问题。并研究了注射成型NdFeB塑料粘结磁体的制备工艺、磁粉表面处理、磁粉含量、添加剂等因素对磁性能、加工性及力学性能的影响，制得了具有较好综合性能的NdFeB塑料粘结磁体，该产品在国内已获得应用。     

Rheology of blends of a thermotropic liquid crystalline polymer with polyphenylene sulfide

Blends of thermotropic liquid crystalline polymer (LCP) and polyphenylene sulfide (PPS) were studied over the entire composition range using Rheometrics Stress Rheometer, capillary rheometer, and differential scanning calorimeter. There is no molecular scale mixing or chemical reaction between the components, as evidenced by melting and crystallization points in the PPS phase. From the strain scaling transients test at low‐rate, LCP and the blends require approximately 60 strain units to obtain steady stale shearing results. The large recoveries in the strain recovery test, magnitude 3 to 3.3 strain unit, are likely the results of texture present in LCPs. With increasing PPS content in LCP/PPS blends, the total recovery declines. Scaling of the transient strain rate remains, but the magnitude of the transients is reduced. At low‐rate, when the LCP is added to the PPS, the pure melts have similar visosity: 500 Pa · s for LCP and 600 Pa · s for PPS, but the viscosity of the blends goes through a maximum with concentration that is nearly three times the viscosity of the individual melts. At high‐rate, a significant depression of the viscosity is observed in the PPS‐rich compositions and this may be due to the fibrous structure of the LCP at high shear rates.