Dynamic fracture testing of polymethyl-methacrylate (PMMA) single-edge notched beam

Dynamic fracture in single-edge notched polymethyl-methacrylate (PMMA) beams have been investigated by three-point-bending impact testing with a drop-weight machine. A high-speed camera combined with the digital image correlation (DIC) method is used to capture the impact-induced crack initiation and propagation, as well as the beam deformation fields and the open mode strain at the original notch tip. The crack propagation length is recorded and the instantaneous crack velocity is calculated. Furthermore, the dynamic fracture toughness K_Id is quantified from the loading-displacement relations at different impact velocities. The effects of the impact velocity and impact energy on dynamic fracture toughness, fracture initiation strain, as well as the corresponding influences on the fracture propagation velocity, are discussed.     

Interpenetrating Polymer Networks of Uralkyd Resin Based on Hydrogenated Castor Oil and Poly(Butyl Acrylate)

Abstract

Semi‐ and full‐interpenetrating polymer networks (IPNs) of uralkyd (UA) resin based on hydrogenated castor oil and poly(butyl acrylate) (PBA) were prepared by the sequential mode of synthesis. These IPNs were characterized for their resistance to thermal behavior, swelling (%), and mechanical properties. The morphology of the IPNs was studied by scanning electron microscopy (SEM). The effect of the variations of the blend ratios on the above‐mentioned properties was examined. The mechanical properties significantly enhanced by increasing UA component in the blend. Full‐IPNs exhibited higher apparent densities, mechanical properties, and thermal stability than the corresponding semi‐IPNs.     

Fracture behavior of amorphous and semicrystalline blends of poly(vinylidene fluoride) and poly(methyl methacrylate)

The fracture behavior of blends of poly(vinylidene fluoride) and poly(methyl methacrylate) was investigated all over the composition range. A detailed analysis of the net stress versus crack opening displacement curves was performed. Fracture surface observations allowed statements on the process zone characteristics ahead of the crack tip. For the amorphous blends, the crack initiation energy is well related to the glass transition temperature. For the semicrystalline blends, the fracture energy is correlated with the degree of crystallinity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

快速pH响应丝胶/聚甲基丙烯酸互穿网络水凝胶的合成及表征

采用同步互穿网络方法制备丝胶蛋白(SS)/聚甲基丙烯酸(PMAA)为组分的互穿网络(IPN)水凝胶. 研究了互穿网络水凝胶对介质pH的刺激响应性能. 结果表明, IPN水凝胶具有强烈的pH刺激响应性能. 在pH=9.2的缓冲溶液中, -COOH解离成 -COO^-, 渗透压与网络之间的静电排斥作用导致IPN的溶胀度增大; 当pH减小时, 溶胀度随之减小. IPN水凝胶具有快速退溶胀速率及可逆溶胀-收缩性能.     

Influence of surface roughness on tribological and mechanical properties of micro-milled and laser ablated poly (methyl methacrylate) PMMA organic glass

Poly (methyl methacrylate) organic glass is used in aircraft windshield application; these structures should have better fatigue and fracture resistance to yield good service life. The tendency towards achieving these properties is lost during manufacturing process. This study aims to determine the effect of grooving on PMMA Organic glass. The grooves are manufactured using two different processes namely Micro-Milling (MM) and Laser Ablation (LA). The tribological properties of laser ablated PMMA (LA-PMMA) and micro-milled PMMA (MM-PMMA) were studied using Pin-on-disc tribometer. The grooved surface roughness of both MM-PMMA and LA-PMMA samples has decreased with increase in wear time, whereas after reaching minimum roughness the coefficient of friction has increased; due to higher adhesion between polymer and sliding metal. The tensile properties of differently machined samples have not shown significant difference; whereas the fracture toughness values were higher with LA-PMMA samples. This effect indicated LA-PMMA had greater capacity to resist crack propagation compare to MM-PMMA samples. Similarly the fatigue endurance limit was found higher with LA-PMMA compared to MM-PMMA, due to better finish of LA-PMMA. Further, the microscopic analysis of laser grooved sample before and after fracture have also shown smoother surface and less conic shapes (fracture point) compare to MM-PMMA.     

Mechanical and fracture behavior of polypropylene/poly(ethylene-co-vinyl alcohol) blends compatibilized with ionomer Na

In this work the deformation and fracture behavior of PP/EVOH blends compatibilized with ionomer Na⁺ at room and low temperature was studied. Uniaxial tensile tests on dumb-bell samples and fracture tests on single-edge notched bending (SENB) specimens were performed for 10 wt.% and 20 wt.% EVOH blends with different ionomer content at 23 °C and −20 °C. The incorporation of EVOH to PP led to less ductile materials in tension as judged by the lower values of the ultimate tensile strain displayed by all PP/EVOH blends in comparison to neat PP. In contrast, the ionomer Na⁺ addition partially counteracted this effect. The compatibilizing effect of ionomer Na⁺ was also evident in fracture results since higher values of the fracture parameter were obtained for the ternary blends. SEM observations also confirmed this effect. On the other hand, PP/EVOH blends exhibited different fracture behavior with test temperature. All blends showed “pseudo stable” behavior at room temperature characterized by apparently stable crack growth that could not be externally controlled. On the contrary, blends behaved as semi-brittle at −20 °C with some amount of stable crack growth preceding unstable brittle fracture. Finally, irrespectively of the temperature or the ionomer content all PP/EVOH blends exhibited more ductile fracture behavior with a higher tendency to stable crack propagation than neat polypropylene.     

Effect of phase change microcapsules on the thermo-mechanical,fracture and heat storage properties of unidirectional carbon/epoxy laminates

This work aims at producing and characterizing unidirectional carbon/epoxy composites containing different fractions of paraffin microcapsules (MC) for thermal management applications. The viscosity of the epoxy/MC mixtures increases with the MC content, thereby increasing the final matrix weight and volume fraction and reducing that of the fibers. This is at the basis of the decrease in mechanical properties of the laminates with high MC concentration (the elastic modulus decreases up to 53% and the flexural strength up to 67%), but the application of theoretical models shows that this decrease is only due to the lower fiber volume fraction, and not to a change in the properties of the constituents or the fiber/matrix interaction. The MC phase is preferentially distributed in the interlaminar zone, which leads to a thickening of this region and a decrease in matrix-related properties, such as the interlaminar shear strength, which decreases of up to 70%. However, a modest MC fraction causes an increase in the mode I interlaminar fracture toughness of 48%, due to the introduction of new toughening mechanisms. On the other hand, an excessive MC content lets the crack propagating through the matrix and not at the fiber/matrix interface, thereby reducing the toughening mechanism provided by fiber bridging. For the thermal properties, the phase change enthalpy increases with the MC fraction up to 48.7 J/g, and this is reflected in better thermal management performance, as proven by thermal imaging tests. These results are promising for the development of multifunctional polymer composites with thermal energy storage and thermal management properties, and future works will be focused on a deeper study of the micromechanical properties of PCM microcapsules and on the improvement of the capsule/matrix adhesion.     

Study of Polymer-Cement Composite Containing Portland Cement and Aqueous Poly (methyl methacrylate) Latex Polymer by Fourier-Transform Infrared (FT-IR) Spectroscopy

The polymer-cement composite is an immiscible band having modified morphology. Polymer phase improves the toughness of brittle cement and has a reinforcing effect, and interactions between cement components and polymers provide stability. In this study, polymer latex [poly(methyl methacrylate), PMMA] – cement paste was prepared with different weight proportions of polymer content. The main scientific objective of this report has been the analysis and the prediction of high strength with the aim of understanding the interactions of PMMA polymer with Portland cement after hydration reaction of cement pastes and curing the specimens for 28 days. The samples were studied by Fourier transform infrared (FT-IR) spectroscopy. The results are critically examined. It is shown that bands support the interaction of PMMA with cement in the composite.     

Deformation and fracture behavior of poly(vinylidene fluoride‐trifluorethylene) ferroelectric copolymer films under uniaxial tension

The deformation and fracture behavior under uniaxial tension was characterized for P(VDF‐TrFE) 68/32 mol % copolymer films prepared under two different processing conditions. It was found that the copolymer films prepared by solution casting and then annealing show a typical polymeric brittle fracture feature. For the copolymer films prepared by stretching the solution‐cast films and then annealing process, a typical linearly strengthening stage occurs in the stress–strain curve after yielding, and the polymer film samples fracture at a much larger maximum strain and a higher tensile strength than those prepared by the former process. SEM observation and XRD analysis were carried out to examine the morphology and microstructure change during uniaxial tension. The results show that for the stretched film samples, the polymer chains undergo slipping or further reorientation during uniaxial tension, causing the increase of the peak intensity in the X‐ray diffraction pattern. For the directly annealed ones, no yielding phenomenon is observed and there is no apparent X‐ray diffraction intensity change. It was suggested that the highly‐oriented fibril structure of the stretched film samples contributes to the linearly strengthening stage after yielding in the stress–strain curve. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3255–3260, 2005     

Miscible blends of polylactide and poly(methyl methacrylate): Morphology,structure, and thermal behavior

The miscibility of polylactic acid (PLA) and atactic poly(methyl methacrylate) (PMMA) blends is investigated as a function of composition. The blends quenched from the melt show the presence of a single glass transition temperature dependent on the composition. The equilibrium melting temperature is determined using the Hoffman‐Weeks method and a depression is observed with increasing content of the PMMA component. The PLA spherulite growth rate and the overall isothermal crystallization rates decrease with increasing the amount of the amorphous component. The increase of the long period value as a function of the PMMA content in the blend is due to the segregation of PMMA component in the amorphous PLA interlamellar regions. The Lauritzen‐Hoffman secondary nucleation theory analysis shows that the segregation of the PMMA in the interlamellar region induces an increase in the surface entropy of folding. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1168–1177     

Helix-sense-selective copolymerization of phenyl[bis(2-pyridyl)]methyl methacrylate,diphenyl(2-pyridyl)methyl methacrylate and triphenylmethyl methacrylate with chiral anionic initiators

Optically active poly[triphenylmethyl methacrylate-co-phenyl[bis(2-pyridyl)]methyl methacrylate] (poly[TrMA-co-PB2PyMA], poly[diphenyl(2-pyridyl)methyl methacrylate-co-phenyl[bis(2-pyridyl)]methyl methacrylate] (poly[D2PyMA-co-PB2PyMA]), and poly[triphenylmethyl methacrylate-co-diphenyl(2-pyridyl)-methyl methacrylate] (poly[TrMA-co-D2PyMA]) were prepared by helix-sense-selective copolymerization with complexes of organolithium with (−)-sparteine [(−)Sp],(S, S)-(+)- and (R, R)-(−)-2,3-dimethoxy-1,4-bis(dimethylamino)butane [(+)- and (−)DDB], and (S)-(+)-2-(1-pyrrolidinylmethyl)pyridine [(+)PMP] as anionic initiators in toluene at low temperature. The copolymers obtained with (−)Sp and (+)DDB or (−)DDB complexes of organolithium showed low optical activity, but to [(+)PMP] complex with N,N′-diphenyleneamine monolithium amide [(+)PMP–DPEDA–Li)] was effective in synthesizing copolymers of high optical rotation ([α] about +320 to + 370°) which were comparable to those of corresponding homopolymers with one-handed helical structure. The optical rotations of poly[TrMA-co-PB2PyMA] and poly[TrMA-co-D2PyMA] were much more stable than that of poly(D2PyMA) or poly(PB2PyMA) in a solution of CHCl₃–2,2,2-trifluoroethanol (10 : 1, v/v) at 25°C, but optical rotation of poly[D2PyMA-co-PB2PyMA] slowly decreased with time in the same conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2127–2133, 1998     

Effects of chain configuration on UCST behavior in blends of poly(L‐lactic acid) with tactic poly(methyl methacrylate)s

Chain configuration influences phase behavior of blends of poly(methyl methacrylate) (PMMA) of different tactic configurations (syndiotacticity, isotacticity, or atacticity) with poly(L ‐lactic acid) (PLLA). Blends system of sPMMA/PLLA is immiscible with an asymmetry‐shaped UCST at ～250 °C. The phase behavior of the sPMMA/PLLA blend is similar to the aPMMA/PLLA blend that has been already proven in the previous work to exhibit similar UCST temperatures (230–250 °C) and asymmetry shapes in the UCST diagrams. On the other hand, the iPMMA/PLLA blend remains immiscible up to thermal degradation without showing any transition to UCST upon heating. The blend system with UCST, that is, sPMMA/PLLA, can be frozen in a state of miscibility by quenching to rapidly solidify from the homogeneous liquid at UCST, where the T_g‐composition relationship for the sPMMA/PLLA blend fits well with the Gordon‐Taylor T_g model with k = 0.15 and the blend's T leads to χ₁₂ = ?0.26 for the UCST‐quenched sPMMA/PLLA blend. Both parameters (k and χ) as characterized for the frozen miscible blend suggest a relatively weak interaction between the two constituents (sPMMA and PLLA) in the blends. The interaction strength is likely not strong enough to maintain a thermodynamic miscibility when the blend is at ambient temperature or any lower temperatures below UCST. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2355–2369, 2008     

Tensile strength and fracture of glass fiber-reinforced plastic (GFRP) plate with an eccentrically located circular hole

In this paper, tensile strength and fracture of finite glass fiber-reinforced plastic GFRP (glass/polyester) composite materials with a through-the-thickness eccentrically located circular hole are experimentally studied. The strain response histories near the hole boundary for different eccentrically located holes during the whole damage and fracture process of the notched specimen are recorded. The effects of off-center distance and hole diameter on strength and fracture of the notched specimen are analyzed. The tensile fracture strength of the notched specimen with an eccentrically located hole is determined. Also, the initial stress concentrations in the composite laminate due to the presence of the eccentrically located hole are understood. These results play an important role for predicting strength and evaluating lifetime of laminate composite with complex geometrical cutouts.     

Synthesis, crystal structure of bis(arylamido)lanthanide methyl complexes and their catalytic behavior for the polymerization of methyl methacrylate

Reactions of [N(C₆H₃i-Pr₂-2,6)(SiMe₃)]₂LnCl(THF) (Ln=Nd, Yb) with two equivalents of MeLi in a mixture solution of toluene and Et₂O gave [N(C₆H₃i-Pr₂-2,6)(SiMe₃)]₂LnCH₃(μ-CH₃)Li(THF)₃·PhCH₃ (Ln=Nd (1), Yb (2)) in good isolated yields as crystalline solids. The single-crystal structural analysis of 2 revealed that the coordination geometry of ytterbium ion is best described as a distorted pseudo-tetrahedron. Both 1 and 2 are active for the polymerization of methyl methacrylate to give syndiotactic-rich and high molecular weight polymers (M_n>10⁴) with relatively narrow molecular weight distributions (M_w/M_n<2).     

Raman spectroscopic investigation of the phase behavior and phase transitions in a poly(methyl methacrylate)‐carbon dioxide system

Laser Raman spectroscopy, in conjunction with an optical high‐pressure cell, was used to investigate the poly(methyl methacrylate)‐carbon dioxide system. The Raman shifts associated with carbon dioxide molecules in the gas phase and those dissolved in the polymer were used to derive sorption kinetics of carbon dioxide and the carbon dioxide‐induced phase changes in the polymer. Measurements were made in the temperature and pressure ranges in which this system is known to exhibit retrograde vitrification behavior. The Raman results on the sorption kinetics and on the onset of plasticization were in agreement with those obtained by gravimetric and calorimetric techniques, respectively. This technique provides a versatile and rapid way of characterizing polymer‐gas systems and information that so far has been obtainable only through painstaking and time‐consuming techniques. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2214–2217, 2003     

Mass spectroscopy and SEC of SRM 1487, a low molecular weight poly(methyl methacrylate) standard

Matrix Assisted Laser Desorption Ionization (MALDI) Time of Flight (TOF) Mass Spectrometry (MS) was used to study the molecular weight distribution (MWD) and the number of α-methyl styrene (α-MeSty) repeat units in SRM 1487, a narrow MWD poly(methyl methacrylate) (PMMA) standard reference material of about 6300 g/mol, which was initiated with α-MeSty. It was found that each PMMA polymer chain had from zero to seven α-MeStys per chain. The MWD of the polymer chains containing a fixed number of α-MeStys was obtained. The MWD, M_w, and the average number of α-MeSty at a given molecular weight from MALDI TOF MS compare well with those obtained from more traditional methods such as ultracentrifugation and Size Exclusion Chromatography (SEC). The implications of the number of α-MeStys per chain is discussed in terms of the chemistry of anionic polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2409–2419, 1997     

Terpolymerization of methyl methacrylate, poly(ethylene glycol) methyl ether methacrylate or poly(ethylene glycol) ethyl ether methacrylate with methacrylic acid and sodium styrene sulfonate: determination of the reactivity ratios

Materials bearing ionic monomers were obtained through free radical terpolymerization of methyl methacrylate (MMA), poly(ethylene glycol) methyl ether methacrylate (PMEM) or poly(ethylene glycol) ethyl ether methacrylate (PEEM) with methacrylic acid (MA) and sodium styrene sulfonate (NaSS). The reactions were carried out in dimethyl sulfoxide using azobis(isobutyronitrile) as initiator. The reactivity ratios of the different couple of monomers were calculated according to the general copolymerization equation using the Finnemann-Ross, Kelen-Tüdos and Tidwell-Mortimer methods. The values of the reactivity ratios indicate that the different monomer units can be considered as randomly distributed along the chains for terpolymerizations of MMA, PMEM or PEEM with MA and NaSS. The average composition of the comonomers in the different terpolymers were calculated, showing a good agreement between the experimental and theoretical compositions. The instantaneous compositions are constant until about 70% of conversion. For higher conversions, the insertion of ionic monomers increases or decreases according to the system studied.     

Processing,mechanical properties,and fracture behavior of cereal protein/poly(hydroxyl ester ether) blends

Blends of poly(hydroxy ester ether) (PHEE), a recently developed bisphenol A ether‐based synthetic biodegradable thermoplastic polymer, with a soybean protein isolate and two hydrolyzed wheat glutens were studied. Blends of the proteins with PHEE were produced from 20 to 70% by weight of protein content. Young's moduli of the protein/PHEE blends fall in the range of 0.8–1.5 GPa with tensile strengths ranging from 10 to 30 MPa. Critical stress‐intensity factors of the blends ranged from 2 to 9 MPa‐m^1/2 depending on the amount of protein added. Morphological analysis indicated a moderate degree of adhesion between the protein and PHEE phases in the blends. In general, as the protein content was increased the materials lost ductility and failed in a brittle manner; however, the mechanical properties of several compositions were comparable to commercial thermoplastics such as polystyrene. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2324–2332, 2002     

Determination of creep compliance,recovery and Poisson's ratio of elastomers by means of digital image correlation (DIC)

This work aims to determine the creep compliance, creep recovery and Poisson's ratio of three common sealing elastomers by means of the digital image correlation (DIC). The tests were conducted by stressing specimens under three different constant stresses during short duration experiments (3 h) to see the prospective of DIC for this application. The strains were measured in x and y axes with time. Thus, the behavior of creep compliance, creep recovery, and the Poisson's ratio of each elastomer were obtained. The creep results exhibited repeatability, as well as, the mean Poisson's ratios estimated were close to reported values for elastomers. Finally, despite of some limitations from the DIC equipment, it was found that this procedure can be implemented as a suitable alternative for the characterization of creep compliance, creep recovery and Poisson's ratio of elastomers. Also, it may be enhanced by following some recommendations given.