POSS增强PMMA热性能和力学性能研究

采用溶液共混法将笼形纳米粒子甲基丙烯酸甲酯基多面低聚倍半硅氧烷（MMA-POSS）与聚甲基丙烯酸甲酯（PMMA）共混制备无机/有机纳米复合材料。利用傅里叶红外光谱仪、核磁共振波谱仪和场发射扫描电子显微镜对材料进行了结构表征。场发射扫描电子显微镜观察复合物薄膜表面形态显示,当MMA-POSS含量较小时,薄膜表面均匀平整,MMA-POSS均匀地分散于PMMA基体中,复合材料的热稳定性和力学性能得到明显改善,其玻璃化转变温度（Tg）和热分解温度（Td）显著提高,POSS含量为1.0 %（质量分数,下同）时,Tg 和Td分别提高了16.9 ℃和21.0 ℃。     

超临界流体制备PMMA/MWCNTs微孔发泡复合材料及其导电性能

通过溶液-熔融共混法制备聚甲基丙烯酸甲酯(PMMA)/多壁碳纳米管(MWCNTs)复合材料,辅以透射电子显微镜对MWCNTs在PMMA基体中的分散性进行表征,发现MWCNTs分散性良好,直径约为10 nm,平均长度约为200 nm.通过超临界流体发泡工艺对PMMA/MWCNTs复合材料导电网络进行调控,从而获得具有不同...     

Influence of Screw Speed on Electrical and Rheological Percolation of Melt‐Mixed High‐Impact Polystyrene/MWCNT Nanocomposites

The influence of screw speed on the electrical and rheological percolation of HIPS/MWCNT composites prepared via melt mixing was investigated. Microscopic examination of these composites using POM, FESEM and HRTEM revealed optimum MWCNT dispersion was achieved at intermediate screw speeds. On addition of MWCNTs to HIPS, the electrical conductivity of HIPS increased by up to 12 orders of magnitude. At screw speeds up to 100 rpm an electrical percolation of 1–3 wt.‐% was achieved. This increased to 3–5 wt.‐% when the screw speed was increased to 150 rpm. The onset of a rheological percolation was detected for an MWCNT loading of 5 wt.‐%, irrespective of screw speed employed. An up‐shift in the Raman G‐band of 24 cm^?1 was observed, implying strong interfacial interaction between HIPS and MWCNTs.

     

Mechanical and surface properties of polyurethane/fluorinated multi‐walled carbon nanotubes composites

To improve the mechanical and surface properties of poly(etherurethane) (PEU), multi‐walled carbon nanotubes (MWCNTs) were surface grafted by 3,3,4,4, 5,5,6,6,7,7,8,8,8‐tridecafluoro‐1‐octanol (TDFOL) (MWCNT‐TDFOL) and used as reinforcing agent for PEU. Fourier‐transform infrared spectroscopy revealed the successful grafting of MWCNTs. PEU filled with MWCNT‐TDFOL could be well dispersed in tetrahydrofuran solution, and tensile stress–strain results and dynamic mechanical analysis showed a remarkable increase in mechanical properties of PEU by adding a small amount of MWCNT‐TDFOL. Contact angle testing displayed a limited improvement (just 9°) in the hydrophobicity of PEU surface by solution blending with MWCNT‐TDFOL. However, a large improvement of surface hydrophobicity was observed by directly depositing MWCNT‐TDFOL powder on PEU surface, and the water contact angle was increased from 80° to 138°. Our work demonstrated a new way for the modification of carbon nanotubes and for the property improvement of PEU. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical Properties of PMMA‐Sepiolite Nanocellular Materials with a Bimodal Cellular Structure

Bimodal cellular poly(methyl methacrylate) with micro‐ and nano‐sized (300–500 nm) cells with up to 5 wt% of sepiolite nanoparticles and porosity from 50% to 75% are produced by solid‐state foaming. Uniaxial compression tests are performed to measure the effect of sepiolite concentration on the elastic modulus and the yield strength of the solid and cellular nanocomposites. Single edge notch bend tests are conducted to relate the fracture toughness of the solid and cellular nanocomposites to sepiolite concentration. The relative modulus is independent of sepiolite content to within material scatter when considering the complete porosity range. In contrast, a mild enhancement of the relative modulus is observed by the addition of sepiolite particles for the foamed nanocomposites with a porosity close to 50%. The relative compressive strength of the cellular nanocomposites mildly decreases as a function of sepiolite concentration. A strong enhancement of the relative fracture toughness by the addition of sepiolites is observed. The enhancement of the relative fracture toughness and the relative modulus (at 50% porosity) can be attributed to an improved dispersion of the particles due to foaming and the migration of micro‐sized aggregates from the solid phase to the microcellular pores during foaming.     

Mechanical reinforcement of poly(1‐butene) using polypropylene‐grafted multiwalled carbon nanotubes

The mechanical properties of poly(1‐butene) reinforced by pristine multiwalled carbon nanotubes (MWNTs) and polypropylene‐grafted MWNTs (PP‐g‐MWNTs) were evaluated. The incorporation of pristine MWNTs to PB led to an improvement in stiffness, but not in strength, ductility, and toughness. In comparison, PP‐g‐MWNTs were able to improve the stiffness, strength, and toughness of PB significantly, without compromising the ductility. The mechanical properties of PB improved with increasing amount of PP‐g‐MWNTs up to an effective MWNT content of 1.5 wt%. Further increase in the effective MWNT content led to a downturn in mechanical properties due to the existence of MWNTs bundles as observed by microscopy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) on miscibility and properties of atactic poly(methyl methacrylate)

Miscibility and properties of two atactic poly(methyl methacrylate)‐based blends [containing 10 and 20% of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)] have been investigated as a function of thermal treatments. Differential scanning calorimetry and dynamic mechanical thermal analysis of blends quenched in liquid nitrogen or ice/water, after annealing at T > 190 °C, showed a single glass transition temperature, indicating miscibility of the components for the time‐temperature history. Two glass transition temperatures, equal to those of the pure components, are instead found for blends after annealing at T < 190 °C. Scanning electron microscopy confirmed the homogeneity for the former quenched blends and phase separation for the latter. These results indicate the presence of an upper critical solution temperature (UCST). Tensile experiments, performed on two series of samples annealed at temperatures above and below the UCST, showed that the copolyester induces a decrease of Young's modulus and stresses at yielding and break points, and a marked increase of elongation at break. Differences in tensile properties between the two series of annealed blends are accounted for by the physical state of the components at room temperature after annealing above or below the UCST. Copyright © 2004 Society of Chemical Industry     

MAP-POSS改性PMMA非等温聚合反应动力学及物理性能

通过共聚将甲基丙烯酰氧丙基笼型倍半硅氧烷（MAP-POSS）引入到聚甲基丙烯酸甲酯（PMMA）中,制备了有机/无机纳米杂化复合材料。用非等温差示扫描量热法研究了MAP-POSS与MMA共聚反应动力学,测定了反应动力学参数,建立了反应动力学数学模型,并测试了其力学、热学及电学性能。结果表明,MAP-POSS与MMA可以共聚,在不降低电性能的情况下,其冲强度提高了约30 kJ/m2,热分解温度提高了34 ℃。     

Anisotropic Electrical Transport Properties of Aligned Carbon Nanotube/PMMA Films Obtained by Electric‐Field‐Assisted Thermal Annealing

This paper demonstrates how the electric‐field‐assisted thermal annealing of octadecylamine‐functionalized SWNT/PMMA films induces an increase in the composite transversal conductivity of several orders of magnitude and a decrease in the lateral conductivity. This difference has been rationalized in terms of the nanotube alignment into the polymer matrix along the electric field direction. This result provides an initial understanding of how electric fields can be used to control the bulk physical properties of such nanocomposites.

     

Poly (N‐methylaniline)/multi‐walled carbon nanotube composites—Synthesis,characterization, and electrical properties

This study described the synthesis of hydrochloric acid (HCl)‐doped poly (N‐methylaniline) (PNMA) with carboxylic groups containing multi‐walled carbon nanotubes (c‐MWNTs) via in situ polymerization. Based on the π–π electron interaction between c‐MWNTs and the N‐methylaniline monomer and the hydrogen bond interaction between the carboxyl groups of c‐MWNTs and imine groups of N‐methylaniline monomers, N‐methylaniline molecules were adsorbed on the surface of c‐MWNTs and polymerized to form PNMA/c‐MWNT composites. Scanning electron microscopy images showed that both the thinner fibrous phase and the larger block phase could be observed. The individual fibrous phases had diameters from several tens to hundreds of nanometers, depending on the PNMA content. Transmission electron microscopy proved that PNMA/c‐MWNTs composite fibrous phases were core (c‐MWNT)‐shell (PNMA) tubular structures. The structure of PNMA/c‐MWNT composites was characterized by FTIR, UV–vis spectra, and X‐ray diffraction patterns. The electrical conductivities of PNMA/c‐MWNT composites were much higher than that of PNMA without c‐MWNTs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2356–2361, 2006     

Thermal degradation behaviour of multi‐walled carbon nanotube‐reinforced poly(L‐lactide) nanocomposites

BACKGROUND: Polymer/multi‐walled carbon nanotube (MWCNT) composites are one of the most promising alternatives to conventional polymer composites filled with micrometre‐sized fillers. This approach can also be applied for the improvement of mechanical properties and thermal stability of biodegradable aliphatic polyesters, such as poly(L ‐lactide) (PLLA), which have been receiving increasing attention due to environmental concerns. Thermal degradation behaviour provides useful information for the determination of the optimum processing conditions and for identification of potential applications of final products. RESULTS: The PLLA/MWCNT composites investigated showed a higher thermal degradation peak temperature and onset temperature of degradation along with a higher amount of residue at the completion of degradation than neat PLLA. Moreover, PLLA/MWCNT composites with a greater MWCNT content showed higher activation energy of thermal degradation than those with a lower MWCNT loading, which confirmed the positive effect of MWCNT incorporation on the enhancement of PLLA thermal stability. CONCLUSION: This study explored the thermal degradation behaviour of PLLA/MWCNT composites by observing the weight loss, molecular weight and mechanical properties during non‐isothermal and isothermal degradation. The incorporation of MWCNTs into the PLLA matrix enhanced considerably the mechanical properties and thermal stability. Copyright © 2009 Society of Chemical Industry     

Synthesis and thermal properties of poly(methyl methacrylate)‐poly(L‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer

Poly(methyl methacrylate)‐poly(L ‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer was prepared using atom transfer radical polymerization (ATRP). The structure and properties of the copolymer were analyzed using infrared spectroscopy, gel permeation chromatography, nuclear magnetic resonance (¹H‐NMR, ¹³C‐NMR), thermogravimetry, and differential scanning calorimetry. The kinetic plot for the ATRP of methyl methacrylate using poly(L ‐lactic acid) (PLLA) as the initiator shows that the reaction time increases linearly with ln[M]₀/[M]. The results indicate that it is possible to achieve grafted chains with well‐defined molecular weights, and block copolymers with narrowed molecular weight distributions. The thermal stability of PLLA is improved by copolymerization. A new wash‐extraction method for removing copper from the ATRP has also exhibits satisfactory results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Physical ageing of polycarbonate and PMMA by dynamic mechanical measurements

The physical ageing properties of polycarbonate and poly(methyl methacrylate) have been measured by dynamic mechanical experiments at different temperatures. It appears that the horizontal shift proposed by Struik to superpose the experimental curves for different ageing times is only a first approximation. The McCrum analysis has been used in the α region but cannot be applied between the α and β relaxations.     

Characterization of Solution‐Processed Double‐Walled Carbon Nanotube/Poly(vinylidene fluoride) Nanocomposites

Dispersion of CNTs in polymers can yield impressive property enhancements at low volume fractions, thus maintaining the inherent processability of the polymer. In particular, they can improve the electromechanical response of piezoelectric polymers by lowering the actuation voltage and increasing strain and stress response. In this work, piezoelectric PVDF and DWNTs are solution‐cast into films. SEM of fracture surfaces confirms good dispersion, and electrical conductivity measurements reveal a low percolation threshold (0.23 vol.‐%). The effect of CNTs on storage modulus, T_c, T_m and T_g of PVDF is studied. Electromechanical strain is observed at low actuation voltages, possibly due to enhanced local electric field in the presence of DWNTs.

     

Physical,mechanical, and thermal properties of PVC/PMMA blends in relation to their morphologies

The effect of blending poly (methyl methacrylate) (PMMA) in various proportions with suitably stabilized and plasticized poly (vinyl chloride) (PVC) was studied with reference to their physical, mechanical, and thermal properties. The resulting morphologies of the various blends were also studied to find a suitable explanation of these properties. The physical and mechanical properties of such polyblends revealed a substantial increase in toughness accompanied with unusual increase in modulus and ultimate tensile strength after an initial drop at the initial stages of PMMA incorporation compared to pure reference compound PVC. The toughening effect, however, undergoes a reduction with increasing proportion of PMMA but it never goes below that of pure PVC (reference compound) within the ranges of PMMA incorporation under study. The various polyblends exhibit the two‐stage degradation typical of PVC and all of them possess higher thermal stability as manifested in their characteristic thermograms. The softening characteristics imparted by PMMA were also reflected in their respective TMA curves. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2721–2730, 2004     

Preparation and characterization of multi‐walled carbon nanotubes/polymer gradient composite films

BACKGROUND: Recently, much work has focused on the efficient dispersion of carbon nanotubes (CNTs) throughout a polymer matrix for mechanical and/or electrical enhancement. However, there are still only few reports about gradient distribution of CNTs in polymer matrices. In the work reported here, CNTs embedded in a polymer film with a gradient distribution were successfully obtained and studied. RESULTS: For composite films with gradient distributions of CNTs, the upper surface behaves as an intrinsic insulator, while the lower one behaves as a semiconductor, or even as a conductor. It is also found that with an increase of 1 wt% CNTs, the resistance of the bottom surface decreases by 2–3 orders of magnitude, as compared with pure polyarylene ether nitrile; furthermore, when the proportion of CNTs increases up to 5 wt%, the resistance of the bottom surface shows only very little change. As a result, sufficient matrix conductivity of the bottom surface could be achieved at a lower filler concentration with CNTs in a gradient distribution. Meanwhile, the thermal stability, glass transition temperature and tensile properties of the matrix are maintained. CONCLUSION: There is considerable interest in such gradient composite films, which could be applied in the electrical engineering, electronics and aerospace fields, for their excellent mechanical properties, thermal stability and novel electrical properties. Copyright © 2008 Society of Chemical Industry     

Morphology,Thermal Stability,and Mechanical Behavior of [Poly(propylene)‐grafted Maleic Anhydride]‐Layered Expanded Graphite Oxide Composites

PP‐g‐MA‐layered EGO composites were prepared directly by solution blending. Two types of PP‐g‐MA/EGO composites were prepared using different mixing methods: distributive and dispersive. In this study, the effects of the mixing method of EGO on the crystalline structure and thermo‐mechanical properties of PP‐g‐MA/EGO composites are reported. WAXD exhibited a shift in 2θ of the monoclinic (α) phase of PP‐g‐MA and (002) EGO peaks for PP‐g‐MA/EGO layered composites, which indicated a modification of the crystalline structure of PP‐g‐MA in the layered composites. DSC exhibited a single characteristic melting peak of monoclinic (α) crystalline phase PP‐g‐MA. The incorporation of EGO increased T_c indicating that the EGO acted as a nucleating agent for PP‐g‐MA. The crystallinity of the PP‐g‐MA/EGO composites was found to be dependent on the mixing method. Thermogravimetry demonstrated that PP‐g‐MA in the presence of EGO has higher degradation temperature, suggesting that the graphite particles acted as a thermal barrier material for PP‐g‐MA. DMA indicated that incorporation of EGO into PP‐g‐MA increased the storage modulus, due to the hydrogen bonding between EGO and MA of PP‐g‐MA.

     

The synthesis of PHA‐g‐(PTHF‐b‐PMMA) multiblock/graft copolymers by combination of cationic and radical polymerization

A new and promising method for the diversification of microbial polyesters based on chemical modifications is introduced. Poly(3‐hydroxy alkanoate)‐g‐(poly(tetrahydrofuran)‐b‐poly(methyl methacrylate)) (PHA‐g‐(PTHF‐b‐PMMA)) multigraft copolymers were synthesized by the combination of cationic and free radical polymerization. PHA‐g‐PTHF graft copolymer was obtained by the cationic polymerization of THF initiated by the carbonium cations generated from the chlorinated PHAs, poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHx) in the presence of AgSbF₆. Therefore, PHA‐g‐PTHF graft copolymers with hydroxyl ends were produced. In the presence of Ce⁺⁴ salt, these hydroxyl ends of the graft copolymer can initiate the redox polymerization of MMA to obtain PHA‐g‐(PTHF‐b‐PMMA) multigraft copolymer. Polymers obtained were purified by fractional precipitation. In this manner, their γ‐values (volume ratio of nonsolvent to the solvent) were also determined. Their molecular weights were determined by GPC technique. The structures were elucidated using ¹H‐NMR and FTIR spectroscopy. Thermal analyses of the products were carried out using differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

In situ Lubrication Dispersion of Multi‐Walled Carbon Nanotubes in Poly(propylene) Melts

An in situ lubrication dispersion method is developed to achieve electrical conductivity in PP containing a small amount of MWCNTs. Good dispersion of the MWCNTs in PP is observed even after a short mixing time because the interactions between the entangled nanotubes are reduced. By in situ lubrication dispersion, the electrical percolation threshold of the PP nanocomposite can be as low as 0.5–0.7 wt% MWCNT. Rheological data also support percolation at 0.5 wt% MWCNT. With 0.5 wt% MWCNT, the slope of G′ at low frequency approaches unity and shows non‐terminal behavior. The proposed dispersion method enhances the wetting of MWCNTs and improves MWCNT dispersion compared to both direct mixing of MWCNT powder with a polymer melt and conventional master batch dilution.

     

Characterization of three‐dimensional braided polyethylene fiber–PMMA composites and influence of fiber surface treatment

Three‐dimensional (3D) braided polyethylene (PE) fiber‐reinforced poly(methyl methacrylate) (PMMA), denoted as PE_3D/PMMA, composites were prepared. Mechanical properties including flexural and impact properties, and wear resistance were tested and compared with those of the corresponding unidirectional PE fiber–PMMA (abbreviated to PE_L/PMMA) composites. Both untreated and chromic acid‐treated PE fibers were used to fabricate the 3D composites in an attempt to assess the effect of chromic acid treatment on the mechanical properties of the composites. Relative changes of mechanical properties caused by fiber surface treatment were compared between the PE_3D/PMMA and PE_L/PMMA composites. The treated and untreated PE fibers were observed by scanning electron microscopy (SEM) and analyzed by X‐ray photoelectron spectroscope (XPS). SEM observations found that micro‐pits were created and that deeper and wider grooves were noted on the surfaces of the PE fibers. XPS analysis revealed that more hydroxyl (? OH) and carboxyl (? COOH) groups were formed after surface treatment. The physical and chemical changes on the surfaces of the PE fibers were responsible for the variations of the mechanical properties of the PE/PMMA composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 949–956, 2006