首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 843 毫秒
1.
It is clearly demonstrated here that ethyl α-(hydroxymethyl)acrylate (EHMA) is a unique monomer for increasing the dimensional stability and physical properties of balsa wood. Copolymers containing EHMA, and especially EHMA-styrene mixtures, were shown to improve the dimensional stability (water soak test) and the absolute mechanical properties of balsa wood. Improvements in specific modulus and specific toughness (absolute properties divided by specific gravity) were achieved using an EHMA-styrene monomer mixture with polybutadiene diacrylate as cross-linker and toughening agent, with the best results obtained at low (10–40%) weight gain. This is the first report that we are aware of describing specific property improvement greater than expected based on density increase. These improvements in modulus and toughness were ascribed to efficient penetration of monomers into the cell walls. Solid-state NMR and scanning electron microscopy confirmed strong interaction of the copolymers generated in situ with wood cell wall components, consistent with the property improvements obtained. The combination of a light-weight, renewable wood precursor with synergistic reinforcement by this combination of monomers offers unique opportunities for increased use of wood-polymer composites in a wide variety of structural and insulating applications. © 1993 John Wiley & Sons, Inc.  相似文献   

2.
Rigid polyurethane foams (RPUFs) were synthesized with bacterial nanocellulose (BNC) at concentrations of up to 0.5 wt% using two insertion routes based on its reaction with the isocyanate precursor (ISO route) and the formation of a colloidal dispersion in the polyol precursor (POL route). The results indicated that, for BNC concentrations of only 0.1 wt%, drastic improvements of the specific elastic compressive modulus (+244.2%) and strength (+77.5%) were measured for foams with apparent density of 46.4+/− 4.7 Kg.m−3. The chemical reaction of BNC with the precursor was corroborated through the measurement of the isocyanate number and FTIR analysis. The BNC caused a significant nucleation effect, decreasing the cell size up to 39.7%. Differential scanning calorimetry analysis revealed that the BNC had a strong effect on post-cure enthalpy, particularly for the POL route. Dynamical mechanical thermal analysis under flexural conditions proved that, regardless of BNC concentration, the incorporation of BNC caused anisotropy and that the ISO route contributed to an enhanced damping factor at high temperatures. These results prove that the ISO route is a key aspect to achieve foamed nanocomposites with improved specific mechanical properties.  相似文献   

3.
This work presents the cellular microstructures and properties of PMMA/graphene nanoribbons (GNRs) microcellular foams. GNRs were obtained by oxidative unzipping multiwalled carbon nanotubes and solvent thermal reduction in dimethylformamide (DMF), then they were mixed with PMMA to fabricate PMMA/GNRs nanocomposites by solution blending. Subsequently, supercritical carbon dioxide (scCO2) as a friendly foaming agent was applied to fabricate PMMA/GNRs microcellular foam by a batch foaming in a special mold. The morphology of cell structure was analyzed by scanning electron microscopy and image software, showing that the addition of a smaller content of GNRs caused a fine cellular structure with a higher cell density (~3 × 1011 cells/cm3) and smaller cell sizes (~1 μm) due to their remarkable heterogeneous nucleation effect. The mechanical testing of PMMA/GNRs microcellular foams demonstrated that the obtained GNRs also could be used as a reinforcing filler to increase the mechanical properties of PMMA foams. An improvement in the compressive strength of ~80% (about 39% increase standardized by specific compressive strength) was achieved by 1.5 wt % GNRs addition, and the thermal stability of PMMA/GNRs foams was enhanced too. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45182.  相似文献   

4.
Homo and copolymerization of isoprene with small amounts (1–10 wt %) of glycidyl methacrylate (GMA) are conducted using controlled‐living radical polymerization mediated by nitroxides at 120 °C and 1170 kPa in solution with toluene (30 wt % solids). N‐tert‐butyl‐N‐(2‐methyl‐1‐phenylpropyl)‐O‐(1‐phenylethyl) hydroxylamine is successfully used as a control agent (unimolecular process) although other controllers are also tested (TIPNO and OH‐TEMPO in a bimolecular process using BPO as initiator). Chain extension experiments demonstrate the livingness of the synthesized materials. Several additives (acetic anhydride, camphorsulfonic acid and glucose) prove effective in accelerating the reactions. All the successful polymerizations result in first‐order kinetics with respect to the monomer, yielding average molecular weights (Mn) of about 75% compared to the theoretical Mn (Mn, theo) with dispersities (Ð) ranging from 1.2 to 1.7 depending on the agent used for control. Controlled grafts of poly(isoprene‐co‐GMA) are also attached to polyisoprene via nitroxide chemistry. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45108.  相似文献   

5.
Nanocellulose reinforced foams are lightweight with improved mechanical properties; however, the strain-rate effect on their mechanical response is not yet fully understood. In this work, rigid polyurethane foams (PUFs) nanostructured with bacterial nanocellulose at 0.2 wt % (BNCF) and without it (PUF) are synthesized and subjected to compression tests at different strain rates. The BNC acts as a nucleation agent, reducing the cell size but maintaining a similar apparent density of 40.4 ± 3.3 kg m−3. Both BNCF and PUF exhibit strain-rate effect on yield stress and densification strain. The BNCF exhibits localized progressive crushing and reduced friability, causing a remarkable recovery in the transverse direction. Numerical simulations show that functionally graded foams subjected to impact could be designed using different layers of PUF and BNCF to vary energy absorption and acceleration rate. The results presented herein warrant further research of the mechanical properties of nanostructured foams for impact applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48701.  相似文献   

6.
This article aims to the development of polylactide (PLA)/triticale straw biocomposites with focus on the relationship between triticale straw content, additive presence, processing, and final properties. Prior to melt compounding, the triticale straw used in this study was chopped using the paper process to produce triticale particles that were further pelletized to assure a consistent feed rate into the extrusion line. PLA/triticale straw biocomposites were obtained for different triticale contents from 10 up to 40%vol, without and with maleic anhydride grafted polylactide (PLA‐g‐MA) as a coupling agent. As a supplementary additive, a PLA‐specific branching agent was used in some selected formulations to minimize the reduction in PLA's molecular weight. The biocomposites were characterized in terms of rheology, thermal properties, morphology, mechanical properties (tensile, flexural, and impact), and recyclability. The PLA‐g‐MA increased the tensile strength of biocomposites by 10%, whereas boosted the tensile modulus about 2.5 times at 40%vol triticale content. For the same formulation, the flexural strength was raised by 15% and flexural modulus was doubled. However, a combination of PLA‐g‐MA and branching agent proved to be the best approach to enhance PLA/triticale straw mechanical properties. When 20%vol of triticale was used as reinforcement, the presence of branching agent increased the flexural strength about 25%. The results demonstrate that the triticale straw processed in this way could offer a similar reinforcement capability as the cellulosic fibers based on the agricultural and forestry resources and can be easily recycled without losing its mechanical properties. It has a good potential in the biocomposites field with promising applications in construction, common goods, and transportation industries. POLYM. ENG. SCI., 54:446–458, 2014. © 2013 Society of Plastics Engineers  相似文献   

7.
A high temperature strain of Chlorella was grown photosynthetically with nitrogen limitation of growth over a range of dilution rates up to the critical value of 0.22 h?1. The “total cell dry weight” is distinguished from the “real biomass” which is total cell dry weight less starch. Nitrogen-limited growth of Chlorella, in terms of real biomass, obeyed the simple Monod model of chemostat culture. In a low EDTA medium (about 1 mol of EDTA per mol Fe3+) ferric hydroxide precipitated at pH 7 and caused iron-limited growth to occur at high dilution rates. Iron precipitation and consequently iron-limited growth, were prevented by increasing the EDTA to 2 mol per mol Fe3+. It was deduced that Fe3+ was available to the cells only as Fe-EDTA complex, not as free Fe3+ in the medium. A glycogen-like starch was stored in the cells and the starch content approached 50% of the total dry weight of cells at low dilution rates. The starch content of the total cell dry weight was practically independent of the growth temperature over the range 28–40°C and the pH over the range 5.5–8.5. The specific rate of starch production (qstarch) reached 0.05 g of starch/g real biomass h.  相似文献   

8.
Bacterial nanocellulose (BNC) was produced by Gluconacetobacter xylinus under static conditions using grape pomace extract (the most abundant residue of the wine industry) as a carbon source and corn steep liquor (a byproduct of corn wet‐milling) as the main nitrogen source. Carbon and nitrogen source concentrations, as well as inocula size, fermentation time, and temperature, were all considered in order to maximize BNC production by the use of statistically designed experiments and the response surface methodology. At optimum production conditions, the effect of fermentation time on morphology, solids content, chemical structure, crystallinity, thermal decomposition pattern, and storage modulus of dried BNC pellicles was analyzed. The results evidenced that dried BNC pellicles that were incubated for longer times showed higher thermal stability, higher crystallinity, and higher storage modulus, resulting from a denser nanoribbons network. All of these characteristics will certainly play a role in the performance of BNC in practical applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43109.  相似文献   

9.
Poly(vinyl alcohol) (PVA)/β‐tricalcium phosphate (β‐TCP, Ca3 (PO4)2) porous composite, which has potential application in articular cartilage repair, was prepared through thermal foaming using water as both plasticizer and physical blowing agent. The effects of β‐TCP content on the foaming behavior, the structure and properties of the porous composites were studied. The results showed that β‐TCP could form hydrogen bonds or coordination interaction with PVA and water; with the incorporation of β‐TCP, the content of nonfreezable bound water in system increased, the water evaporation reduced, beneficial to the controllable foaming of water. The interactions between PVA‐β‐TCP led to the enhanced melt viscosity of PVA. Simultaneously, the β‐TCP particles in matrix could act as heterogeneous nucleation agent to increase the cell density. When β‐TCP content was 7.4 wt %, the porous composite showed the optimal cell structure, i.e., 250 μm average cell size and 87% porosity. The dynamic modulus of the porous composites increased with β‐TCP content and showed frequency‐dependence. The surface contact angle and permeability of the porous composites varied with β‐TCP content, which ranged from 35° to 48° and 11 × 10?14 to 27 × 10?14 m2, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44737.  相似文献   

10.
Sulfonated poly(4,4′‐diphenylether‐1,3,4‐oxadiazole) (POD) composites have been successfully prepared through solution polycondensation of 4,4′‐diphenylether dicarboxylic acid and hydrazine sulfate. The reactions were performed in the presence of various types of pristine carbon nanotubes, i.e. single‐, double‐ and multi‐walled carbon nanotubes, using mild poly(phosphoric acid) as a condensing agent. The POD composites with high molecular weight (of the order of 105 g mol?1) were highly soluble in polar aprotic solvents and thermally stable at temperatures as high as 475 °C. The synthesis method used guaranteed an improved interaction between filler and matrix, thus allowing an enhanced load transfer. The overall performance of the composites was enhanced due to a synergistic reinforcement effect. The nanocomposites exhibited an increase of +33% in storage modulus, +56% in tensile strength and +245% in tensile energy to break. Copyright © 2010 Society of Chemical Industry  相似文献   

11.
This work examines the mechanisms by which magadiite (MGD), a synthetic layered silicate, acts as an active filler to provide high levels of mechanical reinforcement in styrene‐butadiene rubber (SBR) composites. Cetyltrimethylammonium (CTA+) expands the MGD layer spacing and promotes intercalation of SBR and silane coupling agent (Si69); the resulting CMGD/SBR composites have greater tensile moduli than comparable silica/SBR composites. CMGD was reacted in solution with Si69 (or MPTES) to prepare “pre‐grafted” MGD with varying levels of interlayer silane functionalization (SMGD). If the silane graft density is relatively low, the resulting SMGD/SBR composite has mechanical properties comparable to CMGD composites prepared with Si69 added during batch mixing. However, SMGD with high silane graft density does not permit SBR intercalation and produces composites with inferior mechanical properties, demonstrating the necessity of silane‐mediated interlayer grafting. Omitting Si69 from the formulation dramatically reduces the level of mechanical reinforcement as measured by DMA and tensile testing. Adding extra bulk sulfur (to replace sulfur omitted with Si69) does not produce composites with mechanical properties comparable to CMGD/SBR or SMGD/SBR prepared with Si69. This work demonstrates that silane‐mediated SBR‐MGD grafts within the MGD interlayer space are essential for achieving high levels of mechanical reinforcement in MGD/SBR composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45025.  相似文献   

12.
Polyurea nanocomposites represent a promising option in the development of advanced materials for applications that require high mechanical resistance. This article describes an optimized synthetic route for obtaining polyurea nanocomposites with enhanced mechanical properties by employing epoxy‐functionalized multiwalled carbon nanotubes (MWCNTs) as reinforcing agent. The experimental measurements revealed that these functionalized nanofillers have a positive effect on the properties of the composite only until they reach a certain concentration; therefore, the optimal composition was reported (the samples containing 0.2 weight % functionalized MWCNTs). The functionalization of the MWCNTs was confirmed through RAMAN, X‐ray photoelectron spectroscopy, scanning electron microscopy and thermogravimetric analysis, while the polyurea nanocomposites obtained have been characterized by thermal (differential scanning calorimetry and TGA) and mechanical (dynamic mechanical analysis and tensile tests) analyses. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45061.  相似文献   

13.
The acid curing agent content and foaming temperature could be reduced by improving the resol reactivity. In this study, highly active and solid phenol?resorcinol?formaldehyde copolymer resins (PRFRs) with different resorcinol/phenol (R /P ) molar ratios and formaldehyde/(phenol + resorcinol) [F /(P + R )] molar ratios were synthesized through the copolymerization of resorcinol, formaldehyde, and phenol. Phenol?resorcinol?formaldehyde foams (PRFFs) were prepared with synthetic PRFRs. The results showed that PRFR‐2 exhibited higher reactivity, faster curing speed, and better thermal stability. In addition, the foam produced with the PRFR‐2 had improved mechanical and flame retardation properties and a compressive strength of 0.18 MPa, a flexural strength of 0.25 MPa, and a limited oxygen index (LOI) greater than 37%. The increased reactivity of the PRFRs correlated with the changing mechanical properties of PRFFs because of the effects of resorcinol and the molar ratio of formaldehyde to phenol and resorcinol. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44881.  相似文献   

14.
In this investigation, a chiral poly) ester‐imide) (PEI) via direct polyesterification of N,N′‐(pyromellitoyl)‐bis‐(L ‐tyrosine dimethyl ester) and N‐trimellitylimido‐L ‐methionine was prepared using the tosyl chloride/pyridine/N,N′‐dimethylformamide system as a condensing agent. This approach allows the insertion of two natural amino acids into the polymer backbone and the creation of a bioactive polymer. From the chemical point of view, the ester groups impart to the polymer's main and side chain increased sensibility to hydrolysis that can cause chain breaking. Therefore, this polymer is expected to be biodegradable and could be classified as an eco‐friendly polymer. The polymer also had a useful level of thermal stability associated with excellent solubility. PEI/zinc oxide bionanocomposites were subsequently prepared by an ultrasonic method as a simple and inexpensive route, using ZnO nanoparticles (ZnO‐NPs) modified by 3‐aminopropyltriethoxylsilane (KH550) as a coupling agent. The structure and properties of the obtained BNC polymers were confirmed by Fourier transform infrared spectroscopy, X‐ray diffraction, field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The direct proofs for the formation of the true BNC polymers were provided by TEM. Also, the morphology study of the synthesized polymer‐based BNCs showed well‐dispersed ZnO‐NPs in the polymer matrix by FE‐SEM analysis. TGA studies indicated that an increase of the NP content led to an enhancement of the thermal stability of the new BNC polymers. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

15.
Multistage emulsion polymerization was used to prepare ultra‐high molecular weight foam regulator of low cost, with methyl methacrylate (MMA), butyl acrylate (BA), styrene (St) as main raw materials. Ubbelohde viscometer, dynamic light scattering, infrared and raman spectra, TEM, DSC, TGA, and GPC were all used to characterize constituent and structure, morphology, and molecular weight. As a result, when the ratio of soft monomer (BA) and hard monomer (St + MMA) is 1:3, MMA:St = 4:1, potassium persulfate (KPS): 0.15%, sodium hydrogen sulfite (SHS): 0.05%, azodiisobutyronitrile (AIBN): 0.15%, divinyl benzene (DVB): 0.3%, the final product terpolymer has obvious core‐shell structure and ultra‐high molecular weight (Mw = 1,400,000). This kind of foam regulator showed improvements in the melt strength, prevention of bubble coalescence and reduction on cost when compared with the traditional. Finally, the coefficients of poly (methyl methacrylate‐butyl acrylate‐styrene) terpolymer's Mark‐Houwink equation were calculated with tetrahydrofuran (THF) solvent at 25 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44479.  相似文献   

16.
A series of microcellular high temperature vulcanized (HTV) silicone rubber foams were prepared using CO2 as a physical blowing agent. Rheological properties, gas diffusive behavior, and foaming parameters of silicone rubber were investigated. The results show that saturation pressure has a significant effect on the diffusivity of CO2 in HTV silicone rubber matrix. The gas concentration and diffusivity increase from 2.45 wt % to 3.24 wt %, and from 1.62 × 10?5 cm2/s to 7.83 × 10?5 cm2/s as the saturation pressure increases from 2 MPa to 5 MPa, respectively. The value of the gas diffusivity in HTV silicone rubber is almost 1000 times higher than that of the gas diffusivity in polyetherimide (PEI) matrix. Additionally, microcellular HTV silicone rubber foams with the smallest cell diameter of 9.8 μm and cell density exceeding 108 cells/cm3 are achieved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44807.  相似文献   

17.
This work investigates mechanical properties of styrene‐butadiene rubber (SBR) composites incorporating magadiite (MGD), a synthetic layered silicate (Na2Si14O29·9H2O) with surface chemistry similar to precipitated silica used in tire tread formulations. Treatment with cetyltrimethylammonium (CTA+) expands the MGD layers and makes the interlayer face surfaces accessible to sulfur‐functional silane TESPT (Si69) and SBR, primarily during batch mixing. DMA and tensile testing of cured CMGD/SBR composites show that CTA‐treated MGD (CMGD) provides substantially higher levels of mechanical reinforcement than equivalent amounts of silica. However, CMGD/SBR composites exhibit larger loss tangent values above Tg, probably due to lower SBR‐SBR crosslink density resulting from interlayer trapping of sulfur released by Si69 during vulcanization. DMA and tensile testing also demonstrate Si69′s critical role in forming MGD‐SBR graft sites essential to mechanical reinforcement. Replacing silica with CMGD reduces composite weight without sacrificing tensile modulus, suggesting that use of CMGD in tire rubber formulations could improve vehicle energy efficiency. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44763.  相似文献   

18.
Functional cationic polymers carrying mannose moieties were synthesized in a facile manner by employing RAFT polymerization. Initially, a protected carbohydrate based monomer, [2‐(2,3,4,6‐tetra‐O‐acetyl‐α‐d ‐mannopyranosyloxy)ethyl methacrylate (AcManEMA)], was prepared by the O‐glycosylation of 2‐hydroxyethyl methacrylate (HEMA). Subsequently, a macroRAFT agent of poly[2‐(dimethyl)amino ethyl methacrylate] (PDMAEMA) was generated, and a further chain extension polymerization with AcManEMA was carried out in dioxane to form a acetylated mannose cationic diblock copolymer, PDMAEMA‐b‐PAcManEMA. It was attained in high yields and displayed low dispersity (Ð). Acetylated mannose moieties on the polymer were deprotected with sodium methoxide and the amines from the DMAEMA block were protonated to yield a cationic diblock glycopolymer, PDMAEMA‐b‐PManEMA. The cationic property of polymers were characterized by mixing with a negatively charged siRNA duplex and a pDNA, and aggregates of 102 and 233 nm were obtained, respectively. Agarose gel shift assay revealed that the polymers were able to retain the nucleic acids as large polymer complexes. Lectin binding assay proved that the mannose residue on the polymers were only able to bind specifically with ConA. PNA lectin was employed as a control and did not show specific binding. The cationic glycopolymer could be advantageous in targeted nucleic acids delivery in specific cells. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44947.  相似文献   

19.
An experimental study was carried out to investigate the effects of a titanate coupling agent on the mechanical properties, moisture absorption, and thermal conductivity of talc‐filled high‐density polyethylene (HDPE). Talc (0–35 wt %) was used as reinforcement particulate filler in an HDPE matrix and samples were prepared in a micro‐compounder and an injection molding machine. Isopropyl tri(dioctyl)phosphate titanate (0.5 wt %) was used as coupling agent. Composites with and without coupling agent were evaluated for changes in mechanical and thermo‐physical properties, morphology, and void content. Addition of the titanate coupling agent most often resulted in an increase in stiffness and tensile strength. Furthermore, both the void content and the elongation at break of composites were reduced. Results also showed that the coupling agent had no effects on the thermal conductivity, thermal diffusivity, and specific heat capacity of the composites. In addition, it was observed that the coupling agent was more effective at low concentrations of filler. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40449.  相似文献   

20.
ABA‐type amphiphilic triblock copolymers (TBCs) were synthesized by a reversible addition fragmentation chain transfer (RAFT) process with a telechelic polystyrene macro‐RAFT agent and 4‐[n‐(acryloyloxy)alkyloxy]benzoic acid monomers. Ultrafiltration (UF) membranes were fabricated by a phase‐inversion process with blends of the TBC, poly(vinylidene fluoride) (PVDF), and poly(vinyl pyrrolidone) (PVP) in dimethylformamide. The UF‐fabricated membranes were characterized by scanning electron microscopy, atomic force microscopy, water contact angle measurement, thermogravimetric analysis, and differential scanning calorimetry. Pure water permeation, molecular weight cutoff values obtained by the permeation of different molecular weight polymers as probe solutes, bovine serum albumin (BSA) solution permeate flux, and oil–water emulsion filtration tests were used to evaluate the separation characteristics of the fabricated membranes. The tripolymer blend membranes exhibited a higher flux recovery ratio (FRR) after the membrane was washed with sodium lauryl sulfate (0.05 wt %) solution for a BSA solution (FRR = 88%) and oil–water emulsion (FRR = 95%) feeds when than the PVDF–PVP blend membrane (57 and 80% FRR values for the BSA solution and oil–water emulsion, respectively). The pendant carboxylic acid functional moieties in this ABA‐type TBC have potential advantages in the fabrication of high‐performance membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45132.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号