Thermal and dynamic mechanical properties of microwave and heat‐cured poly(methyl methacrylate) used as dental base material

In this study, the particle size distribution, molecular weight, thermal analysis (TGA) differential scanning calorimetry (DSC) and thermogravimetric analysis, and dynamic mechanical analysis (DMA) of poly(methyl methacrylate) used as dental base material were investigated. The commercial raw material used were prepared for microwave curing, and they were cured by microwave and conventional heat methods. The average particle size of the powder studied (103.1 μm) were much larger than that of the commercial powders (50–78 μm) for conventional curing. The particle size dietribution were almost symmetrical and narrow. The viscosity‐average molecular weight were larger for microwave curing and increased with curing time. The glass transition temperature T_g measured (about 110°C) by DSC increased with curing period in microwave oven. The values of T_g were close to each other for both curing techniques. The degradation temperature range observed by TGA were 200–377°C. The movements of molecular chains in their conformations were studied by DMA in the form of changes in different mechanical properties with temperature. It was shown that crosslinking increased with increase of curing time. The changes were more noticeable in microwave curing compared to conventional heat curing. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2971–2978, 1999     

Radiopaque acrylic bone cements with bromine‐containing monomer

One important issue for the acrylic bone cements concerns the radiopacity, which may be achieved by different ways. In this work, a new bromine‐containing acrylic monomer, the 2‐(2‐bromopropionyloxy) propyl methacrylate (BPPM), was synthesized and proposed to be used for providing radiopaque bone cements. Different acrylic bone cements were realized by partially replacing the methyl methacrylate (MMA) monomer phase with 5–20% w/w of BPPM‐comonomer. The effect of this comonomer on the curing parameters of acrylic bone cements, on their thermal and rheological properties, water absorption, density, contact angle, compression tests, and radiopacity was studied. It appears that the presence of BPPM does provide radiopacity, improves the curing parameters by decreasing the maximum curing temperature and increasing the setting time. The new BPPM‐acrylic bone cements exhibit lower glass transition temperature and better thermal stability when compared with the classical radiolucent acrylic cements. Rheological measurements have shown that 10–20% w/w of BPPM in the liquid phase of acrylic bone cement formulations increase its flexibility, and may also induce a slight crosslinking reaction during the curing phase. BPPM‐modified acrylic bone cements present lower polymerization shrinkage and higher compression strength, and similar water uptake, porosity, and water contact angle as the radiolucent PMMA‐cements. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of ingredients on thermal and mechanical properties of acrylic bone cements

There is a very delicate relation between the amounts of all the ingredients present in the cement composition and the properties of the product. In this study, homogeneous poly(methyl methacrylate) (PMMA) microspheres were prepared by suspension polymerization technique, and used in cement formulations. Various acrylic cements with different compositions were prepared by using PMMA microspheres, methyl methacrylate (MMA) monomer, radiopaque agent of barium sulfate (BaSO₄), inorganic particles of hydroxyapatite (HA), initiator and chain stopping agent of 1‐dodecyl mercaptan (DDM). The effects of these additives on mechanical and thermal properties of the resultant cements were examined. Addition of 8% HA relative to the solid parts caused an increase in both tensile and compressive strengths from 20.40 to 25.20 MPa, and from 84.04 to 89.57 MPa, respectively, while curing temperature was decreased about 3 degrees. Chain stopping agent of DDM caused a sharp decrease about 30 degrees in the curing temperature. Radiopaque agent of barium sulfate caused inverse effect on mechanical and thermal properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and dynamic mechanical characterization of acrylic bone cements modified with biodegradable polymers

In this work, a thermal and a dynamic mechanical study of new formulations self‐curing acrylic bone cements is reported. The basic formulation of poly(methylmethacrylate) (PMMA)‐based acrylic bone cements has been modified with biodegradable polyesters such as poly(l ‐lactic acid), poly(β‐hydroxybutyrate), and different kinds of thermoplastic starches. Differential scanning calorimetry (DSC) (dynamic and isothermal conditions), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy (SEM) were used to determine the influence of the biodegradable polymer in the behavior of the biomedical formulations. DSC assay revealed a strong dependence of the polymerization enthalpy (ΔH_cur) with increasing solid : liquid ratio and a low influence of the nature of the added biodegradable polymer on glass transition. TGA analysis showed the different mechanism of PMMA‐biodegradable polymer interaction depending on the solubilization of the added polymer in methylmethacrylate monomer during curing. DMTA showed the reinforcing capacity of segregated phases of the polymer included in the cement. The solubilization of aliphatic polyesters in the resulting PMMA polymerized phase led to a drop in mechanical stiffness observed from storage modulus (E′) profiles. Moreover, tan δ shifts to higher temperatures (4–7°C) during a second scan, confirming the presence of residual monomer content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of flake graphite on property optimisation in thermal conductive composites based on polyamide 66

In this study, in order to improve the thermal conductivity of polyamide 66(PA66), PA66 composites filled with flake graphite (FG) were prepared by twin-screw extruder. Effects of filler content, particle size and particle size mixing on thermal conductivity, mechanical and rheological properties of the composites were investigated. The results showed that as FG content increased from 0 to 50 wt-%, thermal conductivity of the composites filled with 100 μm FG gradually increased, whereas mechanical properties and rheological properties decreased. At 50 wt-% loading, thermal conductivity reached 3.07 W/(m K). With the increase of particle size, thermal conductivity and rheological properties of the composites improved, but mechanical properties increased first and then decreased. The composite filled with 100 μm FG had relatively optimal mechanical properties. Particle size mixing can improve thermal conductivity and the maximum value was achieved in the 1:2 mass ratio of 20 and 100 μm particles.     

Effect of mixed size particles reinforcing on the thermal and dynamic mechanical properties of Al2O3/PPS composites

Thermal and dynamic mechanical properties of polyphenylene sulfide (PPS) composites that were reinforced with different sized alumina (Al₂O₃) particles were studied. These composites were manufactured with two different sizes of Al₂O₃ particles 1 and 63 µm, using microcompounding and injection molding. Monosized Al₂O₃ particles reinforced up to 25 wt% loading content and mixed size Al₂O₃ particles reinforced at 15 wt% loading content as following particle weight proportions: 75% × 63 μm + 25% × 1 μm, 50% × 63 μm + 50% × 1 μm, 25% × 63 μm + 75% × 1 μm. Particle distribution investigations were performed by microcomputerized tomography (micro‐CT). Thermal properties were analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) methods and also dynamic mechanical properties were investigated by dynamic mechanical thermal analysis (DMTA) method. The results showed that mixed size Al₂O₃ particle reinforced composites showed a great enhancement in dynamic mechanical properties without significant change in thermal properties. It was concluded that mixed size particles showed a great synergy to give better results compared with monosized particle reinforced composites. POLYM. COMPOS., 37:3219–3227, 2016. © 2015 Society of Plastics Engineers     

Enhancement of the thermal stability and mechanical properties of a PMMA/aluminum trihydroxide composite synthesized via bead milling

The use of aluminum trihydroxide (ATH) fillers as non-halogen flame retardants for polymethylmethacrylates (PMMA) creates a conflict between the mechanical properties and heat resistance of the composites. Therefore, to ensure that the PMMA mechanical properties remain satisfactory, improvements in both the filler–polymer interactions and the ability to control the size and size distribution, morphology and dispersion of the fillers are required. Thus, in the present study, bead milling was used to control both the size distribution and dispersion of ATH fillers in MMA, which had an initial average size of 0.75 μm. The dispersion was obtained by alteration of the surface characteristics of ATH fillers using a silane-based dispersing agent, (3-acryloxypropyl) trimethoxysilane (APTMS). Bead milling successfully comminuted the ATH particles and prevented the formation of ATH agglomerates. The smallest average size of the ATH particles after bead milling was 300 nm. Highly dispersed ATH filler particles were observed in the TEM images of the PMMA/ATH composites. The filler–polymer interaction, i.e. the interaction parameter (B), was calculated. The effects of volume fraction, particle size distribution, and surface modification of the fillers on the results of dynamic mechanical analysis (DMA) are discussed. The thermal stability of the PMMA/ATH composites was also investigated using thermal gravimetric analysis (TGA).     

Calcium phosphate cements based on alpha-tricalcium phosphate obtained by wet method: Synthesis and milling effects

Calcium phosphate cements present many advantages for their use as bone substitute, among which biocompatibility and bioactivity. However, these cements generally have low mechanical strength compared to the bones of human body. This work aims to develop a method to produce calcium phosphate cements based on alpha-tricalcium phosphate and to evaluate the influence of milling time (0–16 h) on their particle size and mechanical properties. The obtained powder was characterized by particle size analysis and X-ray diffraction. The proposed method allowed to obtain highly pure alpha-tricalcium phosphate. The milling resulted in different average particle size, showing a decrease of around 83% with 16 h of milling. Specimens were prepared and evaluated by apparent density, microstructure by scanning electron microscopy and compressive strength. The variation of the average particle size influenced the compressive strength whose best result was obtained for the sample without additional milling.     

端氨基丁腈橡胶增韧环氧-聚酰胺胶粘剂的研究

通过DSC,扫描电镜分析及剪切和剥离强度性能测试研究了端氨基液体丁腈橡胶(ATBN)改性环氧-聚酰胺体系的固化动力学,粘接性能及增韧相态。结果表明,根据Ellerstein法和峰值法计算得到的固化反应活化能分别为为73.6 kJ/mol和65.7 kJ/mol,体系最佳固化温度为41～97℃。固化体系中橡胶相粒径大小对胶粘剂性能有较大影响,60℃和室温固化体系分散相粒子平均粒径分别为1～2μm,0.5μm。粒径1～2μm时体系的增韧效果最佳,粘接性能优异。     

Study on PVC composites containing Eugenia jambolana wood flour

This article describes the properties of composites using unplasticized PVC matrix and wood flour (obtained by crushing the bark of Eugenia jambolana) as filler. Composites were prepared by mixing PVC with varying amounts of wood flour (ranging from 10–40 phr; having particle sizes of 100–150 μm and <50μm) using two‐roll mill followed by compression molding. The effect of wood flour content and its particle size on the properties, i.e., mechanical, dynamic mechanical, and thermal was evaluated. Tensile strength, impact strength, and % elongation at break decreased with increasing amounts of wood flour. Stiffness of the composites (as determined by storage modulus) increased with increasing amounts of the filler. Modulus increased significantly when wood flour having particle size <50 μm was used. Morphological characterization (SEM) showed a uniform distribution of wood flour in the composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Properties of novel PMMA‐co‐EHA bone cements filled with hydroxyapatite

To design bone cements with predictable intraoperative and postoperative behavior, researchers must understand how cement formulations affect the polymerization reaction and specially the properties of the end product. In this study, a bioactive filler (commercial hydroxyapatite, HA) was incorporated into poly(methyl methacrylate)‐co‐ethyl hexyl acrylate (PMMA‐co‐EHA) matrices to prepare new bone cement formulations. The new PMMA‐co‐EHA/HA composites were obtained by varying the relative contents of the monomers, MMA, and EHA. The resulting composites were evaluated in terms of the curing parameters, water uptake and weight loss in phosphate buffer solution and mechanical properties. The results obtained showed that incorporation of 25% HA particles induced major changes in the final properties of the bone cements comparing with the unfilled parent matrices. In particular, the peak temperature decreased and the setting time and the bending elastic modulus increased in all formulations containing HA particles. Composites with low EHA content exhibited a decrease in strength after HA incorporation, which was attributed to the poor interfacial adhesion between the components of the composites. Additionally, the immersion results showed that the amount of 25% HA (regarding the total mass) in the composites was not enough to induce in vitro bioactive properties in the materials. POLYM. COMPOS., 35:759–767, 2014. © 2013 Society of Plastics Engineers     

Effect of microencapsulated curing agents on the curing behavior for diglycidyl ether of bisphenol A epoxy resin systems

Microcapsules containing a curing agent, 2‐phenyl imidazole (2PZ), for a diglycidyl ether of bisphenol A (DGEBA) epoxy resin were prepared by a solid‐in‐oil‐in‐water emulsion solvent evaporation technique with poly(methyl methacrylate) (PMMA) as a polymeric wall. The mean particle size of the microcapsules and the concentration of 2PZ were about 10 μm and nearly 10 wt %, respectively. The onset cure temperature and peak temperature of the DGEBA/2PZ–PMMA microcapsule system appeared to increase by nearly 30 and 10°C, respectively, versus those of the DGEBA/2PZ system because of the increased reaction energy of curing. The former could take more than 3 months at room temperature, whereas the latter was cured after only a week. The values of the reaction order (a curing kinetic parameter) for DGEBA/2PZ and DGEBA/2PZ–PMMA microcapsules were quite close, and this showed that the curing reactions of the two samples proceeded conformably. The curing mechanism was investigated, and a two‐step initiation mechanism was considered: the first was assigned to adduct formation, whereas the second was due to alkoxide‐initiated polymerization. The glass‐transition temperature of DGEBA/2PZ was 165.2°C, nearly 20°C higher than the glass‐transition temperatures of DGEBA/2PZ–PMMA microcapsules and DGEBA/2PZ/PMMA microspheres, as determined by differential scanning calorimetry measurements. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and properties of polytetrafluorethylene filled ethylene–propylene–diene monomer composites

Ethylene–propylene–diene monomer/polytetrafluorethylene (EPDM/PTFE) composites based on EPDM and electron beam irradiated PTFE powders (MS‐II, MS‐III, and MS‐V, with mean diameter 5 μm, 1 μm, and 0.1 μm, respectively) were prepared by a mechanical compounding technique. The curing characteristics, morphologies, mechanical properties, and abrasion behaviors of these composites were investigated. The curing measurements indicated that the addition of lower loading of MS‐III or MS‐V enhanced the lubrication of EPDM compounds and delayed the curing process. The morphological structure of the composites demonstrated that the MS‐III and MS‐V were uniformly dispersed in EPDM matrix and the efficient polymer–filler interfacial interactions were constructed. In comparison with EPDM/MS‐II and EPDM/MS‐III, EPDM/MS‐V exhibited outstanding tensile strength, tear strength, elongation at break, and abrasion resistance due to the nanometer particle dimension and good dispersion of MS‐V as well as the stronger interfacial interactions between MS‐V and the EPDM matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of filler loading on the mechanical properties of crosslinked 1,2,3‐triazole polymers

The effect of filler loading on the mechanical properties of crosslinked triazole polymers obtained by polymerization of E300 dipropiolate ( 1 ) with diazide ( 2 ) obtained from tetraethylene glycol using tetraacetylene functionalized crosslinker ( 3 ) was studied systematically. Aluminum (10–14 μm) was used as the primary filler during the formulations; the effect of secondary fillers such as aluminum (<75 μm), NaCl (45–50 and 83–105 μm) was studied with the increase in the total filler loading. The modulus of the aluminum‐filled crosslinked triazole polymers increases with the increase in the filler content while using either particle sized aluminum powder. The use of Al (particle size <75 μm) and NaCl (particle size 45–50 μm and 83–105 μm) as secondary or additional fillers while using aluminum (10–14 μm) as the main filler, has a diminishing effect on the modulus and strain of the crosslinked triazole polymers. Triazole polymers described herein have the ability to wet and adhere to large quantities of these inorganic salts and thus maintain mechanical properties of the composite comparable to typical polyurethane elastomeric matrices, regardless of the chemistry of the particulate filler, which imparts an important and necessary binder characteristic for energetic composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation,modification, and characterization of acrylic cements

Acrylic cements with different compositions were prepared by mixing the solid part (composed of poly(methyl methacrylate), PMMA, and benzoyl peroxide, BPO) and the liquid part (composed of methyl methacrylate, MMA, and N,N‐dimethyl‐p‐toluidine, DMPT), modified by addition of hydroxyapatite (HA) and ammonium nitrate (AN) and characterized by measuring thermal and mechanical properties. Three sets of samples were prepared. For B‐group, the total amount of solid including HA was constant but the PMMA to HA ratio was varied. For C‐group, polymer/monomer ratio was constant and varying amounts of HA was added. For D‐group, polymer/monomer ratio was kept constant and AN was added in varying amounts. Effects of these composition changes on the properties of the cement such as setting time, curing temperature, tensile and compression strength, and deformation were examined. For B‐group samples, no linear change was observed in thermal (curing temperatures were all quite high) and mechanical (between 27 and 19 MPa for tensile, and 98 and 116 MPa for compression strength) properties upon change of HA content with change in solid/liquid ratio. For C and D‐group samples, a continuous decrease in curing temperature from 114 to 101°C and from 94 to 73°C was observed upon increasing HA and AN contents, respectively. Also, a linear relation was observed in compression strength (from 98 to 111 MPa) and in tensile strength (from 27 to 21 MPa) upon HA addition, and in the compression strength (from 103 to 85 MPa) and in the tensile strength (from 22 to 17 MPa) with NA addition. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3631–3637, 2006     

Preparation and curing behavior of latent 2-PhIm-PS microcapsule curing agent for epoxy resin

A core–shell microcapsule latent epoxy curing agent (2-PhIm-PS) is obtained by solvent evaporation method with 2-phenyl imidazole (2-PhIm) as the core material and polystyrene (PS) as the wall material. The microcapsule parameters, morphology, structure, curing behavior, and the mechanic properties of cured epoxy resin with this microcapsule latent curing agent were characterized through comparing with 2-PhIm. The particle size distribution of the microcapsule is narrow, the average particle size is about 10.56 μm, and the core material content is 23%. The prepared 2-PhIm-PS microcapsule curing agent has excellent latent curing properties. It can completely cure epoxy resin E-51 within 10 min at 130°C, and its latent period can be more than 40 days at room temperature. In addition, the curing kinetics of one-component epoxy resin curing system (E-51/2-PhIm-PS) composed of 2-PhIm-PS microcapsules and epoxy resin E-51 is also studied by using Kissinger equation, Flynn–Wall–Ozawa and Crane formula. The results provide an outline for the evaluation on the applicability of the microcapsule curing agent of 2-PhIm-PS for epoxy resin.     

不同粒度碳化硅对莫来石基浇注料性能的影响

以莫来石、铝矾土为主要原料,铝酸钙水泥为结合系统,分别研究了不同粒度的碳化硅经过不同热处理温度后对莫来石基浇注料性能的影响。试样自然干燥24h脱模后,再经110℃烘干24h,分别于1000℃,1300℃和1500℃热处理3h。检测各温度热处理后试样的线变化率、体积密度、抗折强度、耐压强度以及试样的线胀系数。结果表明,不同粒度的碳化硅对调整浇注料中温的线变化率无明显作用。本实验中,含有粒度75μm SiC的浇注料的体积密度最大,并且含有该粒度SiC的浇注料的力学性能最好。     

Mechanical and flame-resistance properties of polyurethane-imide foams with different-sized expandable graphite

Polyurethane-imide (PUI) composite foams with expandable graphite (EG) of different sizes were prepared by a polyimide prepolymer method. EG particles were treated with a silane coupling agent to improve compatibility with the foam. The effect of EG particle size on cell morphology, thermal degradation, flame-resistance and mechanical properties of PUI foams was investigated. Results showed that the mean cellular diameter of foams with EG particle was much higher than that of foams with surface-modified EG particle at the same filler loading. When filler particle diameter increased from 20 to 90 μm, the compressive strength, density and closed-cell ratio of foams increased, and then decreased when filler particle diameter further increased from 90 to 150 μm. Thermal stability of foams increased with the increasing filler particle diameter from 20 to 50 μm, and decreased with the increasing filler particle diameter from 50 to 90 μm. The limited oxygen index (LOI) value of foams with surface-modified EG increased from 24.8% to 32.1% when EG particle diameter was below 90 μm. Foams with surface-modified EG exhibited enhanced mechanical properties, thermal stability and flame resistance than foams with neat EG at the same loading.     

Model filled rubber. VI: Dynamic property dependence on filler particle size of rubber compounds during curing

The effect of particle size on curing kinetics and dynamic properties was examined with model filled rubber compounds containing monodisperse size crosslinked polystyrene (PS) particles synthesized from emulsifier‐free emulsion polymerization. In the process of curing, the magnitude of the dynamic moduli increased and the gelation time (GP) decreased as PS particle diameter decreased from 1.25 to 0.315 μm. GP was 5.5 hours for the pure matrix, 13 minutes for the composite containing 0.315 μ.m particles, 1.4 hours for 0.688 μm particles and more than 2 hours for 1.25 μm particles. We propose that in PS particle filled systems, the ability to form clusters was due to interparticle dispersive interactions which increase with decreasing particle size. The particle clusters function as physical crosslinks, so that the overall crosslink density was significantly enhanced. Rheologically, the dynamic moduli and gelation rate were increased with decreasing particle diameter.     

Microstructural,mechanical, and thermal‐insulation properties of poly(methyl methacrylate)/silica aerogel bimodal cellular foams

Novel poly(methyl methacrylate) (PMMA)/silica aerogel bimodal cellular foams were prepared by melt mixing and a supercritical carbon dioxide foaming process. The effects of the silica aerogel content on the morphologies and thermal‐insulating and mechanical properties of the foams were investigated by scanning electron microscopy, mechanical tests, and heat‐transfer analysis. The experimental results show that compared to the pure PMMA foam, the PMMA/silica aerogel microcellular foams exhibited more uniform cell structures, decreased cell sizes, and increased cell densities (the densities of the foams were 0.38–0.45 g/cm³). In particular, a considerable number of original nanometric cells (ca. 50 nm) were evenly embedded in the cell walls and on the inner surfaces of the micrometric cells (<10 μm). A 62.7% decrease in the thermal conductivity (0.072 W m⁻¹ K⁻¹) in comparison to that of raw PMMA after 0.5 wt % silica aerogel was added was obtained. Mechanical analysis of the PMMA/silica aerogel foams with 5 and 2 wt % silica aerogel showed that the compressive and flexural strengths were distinctly improved by 92 and 52%, respectively, and the dynamic storage moduli increased. The enhanced performance showed that with the addition of silica aerogel into PMMA, one can obtain thermal‐insulation materials with a favorable mechanical strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44434.