The effect of transcrystallinity on the transverse mechanical properties of single-polymer polyethylene composites

The microstructure of polyethylene (PE)/PE composites, consisting of the high-density PE (HDPE) matrix and ultrahigh molecular-weight PE (UHMWPE) fibers, was investigated. Single-fiber composites were prepared and analyzed in a hot-stage crystallization unit attached to a polarizing microscope, aiming to find out how the conditions of crystallization affected the transcrystallinity (tc) growth at the fiber-matrix interface. Thermal treatments leading to two extreme microstructures, of either maximum or minimum thickness of the transcrystalline zone, were sought. It was found that a uniform transcrystalline layer was developed on the UHMWPE fiber from the HDPE melt under isothermal conditions, whereas rapid cooling from the melt prevented the generation of tc. The mechanical properties of unidirectional composite laminae either with or without the transcrystalline zone were measured. A comparison of the transverse strength predicted by theoretical models with the experimental values revealed good interfacial adhesion in the PE/PE system. It was shown that the tc growth had a negligible effect on the composite mechanical properties in the longitudinal direction, whereas it resulted in a 50% decrease of the transverse tensile strength and strain to failure. Scanning electron microscopy attributed that observation to premature brittle failure at tc/tc contact regions. © 1995 John Wiley & Sons, Inc.     

Effect of anisotropy on photo-mechanical oxidation of polyethylene

Blown polyethylene (PE) film was exposed to UV irradiation while under tensile stress. Tests were conducted on unpigmented PE and on a series of five PEs containing TiO₂ pigments with different photo-activities. The yield strengths measured in tensile tests on unexposed films were typically 10% greater in the longitudinal (machine) direction than in the transverse direction. UV exposures were conducted with stress applied both parallel and transverse to the machine direction. The chemical degradation was followed using the FTIR carbonyl index. For all six materials, tensile stress accelerated carbonyl group development. Some samples cracked during UV exposure in tension and did so in a shorter time if the stress was applied in the machine direction than if it was transverse to it. The carbonyl index at the onset of cracking was lower for longitudinal samples than for transverse samples.Unpigmented PE was slightly more sensitive to transverse strain and the anatase-pigmented PE slightly more sensitive to longitudinal strain. The carbonyl production rate for two of the rutile pigmented grades showed very little dependence on the straining direction whereas for a third the increase in rate was significantly greater when the deformation was applied in the machine direction than for transverse stretching. With the fourth rutile-pigmented grade, transverse stretching produced the greater effect. These differences cannot be correlated with the photoactivity of the different pigments. The highest ratios of longitudinal/transverse enhancement were found with the least photoactive rutile pigment and with anatase—the most photoactive of all those tested.     

An alternative method for in vitro fire smoke toxicity assessment of polymers and composites using human lung cells

An alternative method for in vitro fire smoke toxicity assessment of polymers and composites using human lung cells has been investigated. A range of building and train interiors including polyethylene (PE), polypropylene (PP), polycarbonate (PC), polymethyl methachrylate (PMMA), polyvinyl chloride (PVC), fiberglass‐reinforced polymer (FRP), and melamine‐faced plywood (MFP) were studied. The exposure of combustion toxicants to human lung cells (A549) at the air/liquid interface was acquired using a Harvard Navicyte Chamber. Cytotoxic effects on human cells were assessed based on cell viability using the MTS assay (Promega). Cytotoxicity results were expressed as no observable adverse effect concentration (NOAEC), 10% inhibitory concentration (IC₁₀), 50% inhibitory concentration (IC₅₀), and total lethal concentration (TLC) values (mg/l). Mass loss data and toxic product yield were also determined. Results suggested that PVC (IC₅₀ 1.99 mg/l) was the most toxic materials followed by PP, FRP‐16, PC, PMMA, FRP‐10, PE, and melamine plywood. Some materials revealed to be more toxic under flaming combustion (PP, PC, FRP‐16, and FRP‐10), while others (PVC, PMMA, PE, and melamine plywood) appeared more toxic under non‐flaming combustion. The method developed can be used to screen the toxicity of materials which would be important information in building and mass transport material selection. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal behaviour of polyethylene‐block‐poly(methyl methacrylate) block copolymer: effect of multiple heating and cooling rates versus mathematical artefact

The melting and crystallization behaviours of a polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) diblock copolymer and a PE homopolymer were investigated using multiple heating and cooling rate differential scanning calorimetry (DSC) experiments, and modelling of the crystallization kinetics and lamellar thickness distribution. This new model was first validated applying literature and experimental data. The model‐predicted morphology (n = 3.2) closely matched the spherulitic morphology (n = 3), which was determined using polarized optical microscopy. For each experimental cooling rate, the model predicted diblock copolymer crystallinity that well matched the entire DSC crystallinity curve, notably for an Avrami–Erofeev index of n = 2; and apparent crystallization activation energy that hardly varied with the cooling rates used, relative crystallinity (α), and crystallization temperature or time. This disfavours the concept of variable activation energy. The use of the right crystallization model and parameter estimation algorithm is important for addressing the mathematical artefact. Under non‐isothermal cooling, the PE‐b‐PMMA diblock copolymer, as per the model prediction, crystallized without confinement (n ≠ 1), preserving the cylindrical structure. From the characteristic shapes of the crystallization function f(α(T)) versus 1/T and crystallization rate versus α plots, the resulting T_cmax and narrow α_max range can guide the search for an appropriate crystallization model. The overall treatment illustrated in this study is not restricted to a PE homopolymer and a PE‐b‐isotactic PMMA block copolymer. It can be generally applied to crystalline homopolymers and copolymers (alternating, random and block), as well as their blends. The block copolymers and blends can be crystalline–amorphous as well as crystalline–crystalline. © 2014 Society of Chemical Industry     

Comparison of irreversible deformation and yielding in microlayers of polycarbonate with poly(methylmethacrylate) and poly(styrene‐co‐acrylonitrile)

Microlayers of polycarbonate (PC) with poly(methylmethacrylate) (PMMA) or poly(styrene‐co‐acrylonitrile) (SAN) were processed with varying layer thicknesses. Adhesion between PC and PMMA was found to be an order of magnitude higher than between PC and SAN, as determined with the T‐peel method. To probe the effect of the adhesion difference on yielding and deformation of PC/PMMA and PC/SAN microlayers, the macroscopic stress–strain behavior was examined as a function of layer thickness and strain rate, and the results were interpreted in terms of the microdeformation behavior. During yielding, crazes in thick SAN layers opened up into cracks; however, PC layers drew easily because local delamination relieved constraint at the PC/SAN interface. Adhesion of PC/PMMA was too strong for delamination at the interface when PMMA crazes opened up into cracks at low strain rates. Instead, PMMA cracks tore into neighboring PC layers and initiated fracture. At higher strain rates, good adhesion produced yielding of thick PMMA layers, a phenomenon not observed with thick SAN layers. The change in microdeformation mechanism of PMMA with increasing strain rate produced a transition in the yield stress of PC/PMMA microlayers. Microlayers of both PC/SAN and PC/PMMA with thinner layers (individual layers 0.3–0.6 μm thick) exhibited improved ballistic performance compared to microlayers with thicker layers (individual layers 10–20 μm thick), which was due to cooperative yielding of both components. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1545–1557, 2000     

Viscoelastic properties of blends of poly(methyl methacrylate) and poly(styrene‐co‐acrylonitrile) having various acrylonitrile contents

Dynamic viscoelastic properties of blends of poly(methyl methacrylate) (PMMA) and poly(styrene‐co‐acrylonitrile) (SAN) with various AN contents were measured to evaluate the influence of SAN composition, consequently χ parameter, upon the melt rheology. PMMA/SAN blends were miscible and exhibited a terminal flow region characterized by Newtonian flow, when the acrylonitrile (AN) content of SAN ranges from 10 to 27 wt %. Whereas, PMMA/SAN blends were immiscible and exhibited a long time relaxation, when the AN content in SAN is less than several wt % or greater than 30 wt %. Correspondingly, melt rheology of the blends was characterized by the plots of storage modulus G′ against loss modulus G″. Log G′ versus log G″ plots exhibited a straight line of slope 2 for the miscible blends, but did not show a straight line for the immiscible blends because of their long time relaxation mechanism. The plateau modulus, determined as the storage modulus G′ in the plateau zone at the frequency where tan δ is at maximum, varied linearly with the AN content of SAN irrespective of blend miscibility. This result indicates that the additivity rule holds well for the entanglement molecular weights in miscible PMMA/SAN blends. However, the entanglement molecular weights in immiscible blends should have “apparent” values, because the above method to determine the plateau modulus is not applicable for the immiscible blends. Effect of χ parameter on the plateau modulus of the miscible blends could not be found. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Strain ratio and volume change during tension and compression creep of thermoplastics

Creep tests up to 10⁶ seconds in tension and compression were conducted on polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and polypropylene (PP). Measurements of longitudinal and lateral strain provided values for tension and compression strain ratio. These increased with time and stress for PMMA and PVC from about 0.38 to 0.44. The results for PP increased from 0.44 to above 0.5 in. tension and showed a decreasing ratio in compression, which suggested a time and stress dependent structural change. Volumetric strain was computed from the linear strains and plotted against stress and axial strain. Except at 10² seconds, the relationships were non-linear up to volumetric strains of about 0.3% and in the cases of PMMA and PVC there were greater changes of volume in tension than compression.     

Relationship between the composition of polycarbonate copolymers and the refractive index

With a polycarbonate (PC)–poly(methyl methacrylate) (PMMA) graft copolymer and a PC–poly(dimethyl siloxane) (PDMS) block copolymer, the relationship between the composition of PC copolymers and the refractive index (n_D) was investigated. According to the results, with a PMMA content of 38 wt %, the n_D value of the PC–PMMA graft copolymer was nearly the same as that of electrical (E) glass (n_D = 1.545), and with a PMMA content of 6 wt %, it was nearly the same as that of electrical corrosion resistance (ECR) glass (n_D = 1.579). However, with a PDMS content of 19 wt %, the n_D value of the PC–PDMS block copolymer was nearly the same as that of E glass, and with a PDMS content of 2 wt %, it was nearly the same as that of ECR glass. The combination of the PC–PDMS block copolymer and the glass fibers (GFs) of ECR glass led to haze values of 8 and 16% with GF contents of 10 and 20%, respectively. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 514–521, 2002; DOI 10.1002/app.2355     

Mechanical performance of ternary in situ polycarbonate/poly(acrylonitrile‐butadiene‐styrene)/liquid crystalline polymer composites

Ternary in situ polycarbonate (PC)/poly(acrylonitrile‐butadiene‐styrene) (ABS)/liquid crystalline polymer(LCP) composites were prepared by injection molding. The LCP used was a versatile Vectra A950, and the matrix of composite specimens was PC/ABS 60/40 by weight. Maleic anhydride (MA) copolymer and solid epoxy resin (bisphenol type‐A) were used as compatibilizers for these composites. The tensile, dynamic mechanical, impact, morphology, and thermal properties of the composites were studied. Tensile tests showed that the tensile strength of the PC/ABS/LCP composite in the longitudinal direction increased markedly with increasing LCP content. However, it decreased slowly with increasing LCP content in the transverse direction. The modulus of this composite in the longitudinal direction appeared to increase considerably with increasing LCP content, whereas the incorporation of LCP into PC/ABS blends had little effect on the modulus in the transverse direction. The impact tests revealed that the Izod impact strength of the composites in both longitudinal and transverse direction decreased with increasing LCP content up to 15 wt %; thereafter it increased slowly with increasing LCP. Dynamic mechanical analyses (DMA) and thermogravimetric measurements showed that the heat resistance and heat stability of the composites tended to increase with increasing LCP content. Scanning electron microscopy observation and DMA measurement indicated that the additions of epoxy and MA copolymer to PC/ABS matrix appeared to enhance the compatibility between the PC and ABS, and between the matrix and LCP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2274–2282, 1999     

Solvent cast blends of PMMA microspheres in bisphenol-A-polycarbonate

Abstract

Transparent films of bisphenol-A-polycarbonate (PC), poly (methyl methacrylate) (PMMA) microspheres and their blends at various compositions were prepared by solution casting using methylene chloride (MC) as a solvent. The structural, morphological and thermal properties were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry and thermogravimetric analysis. It was obvious that all the characteristic absorption bands could be found in the IR spectra of PC/PMMA blends, but different in the strength. From the SEM images, a co-continue morphology was observed in the PC/PMMA blends when the PMMA content was above 80wt%, indicating the existence of special interaction between PC and PMMA microspheres. Differential scanning calorimetry results showed a single glass transition temperature (T_g) only for 10%PC/90%PMMA blends because of the better dissolution of PC in PMMA than PMMA in PC. Thermogravimetric analysis thermograms showed that the thermal stability of PC/PMMA blends increased with increasing PC content, which was due to the better thermal stability of PC.     

THE CONFORMATIONAL MECHANISM OF THERMOELASTICITY OF ORIENTED POLYETHYLENE

Temperature variations of oriented polyethylene (PE) with a draw ratio of ～ 450% were measured in longitudinal adiabatic tension and compression (along the orientation axis) and transverse compression. Stress-strain curves (for tension and compression) were recorded. Linear thermal expansion coefficients in the longitudinal and transverse direction were measured. Thermoelastic characteristics and also thermal properties of oriented PE were quantitatively analyzed. It has been concluded that conformational dynamics has a dominating influence on these characteristics.     

Lipid class composition of the protozoan Perkinsus marinus, an oyster parasite, and its metabolism of a fluorescent phosphatidylcholine analog

Perkinsus marinus is one of two important protozoan parasites of the eastern oyster, Crassostrea virginica. The other is Haplosporidium nelsoni. Lipids extracted from 7-d-old in vitro cultured P. marinus meronts, incubated with fluorescent-labeled phosphatidylcholine (FL PC) and nonincubated P. marinus meronts, were analyzed by a high-performance liquid chromatography (HPLC) system equipped with a diol phase column, in combination with thin-layer chromatography coupled with a flameionization detector (TLC/FID), and high-performance thin-layer chromatography (HPTLC). Various polar and neutral lipid classes were separated by HPLC using a two-gradient solvent system. Five polar lipid classes—phosphatidylcholine (PC), phosphatidylethanolamine (PE), cardiolipin (CL), sphingomyelin (SM), and phosphatidylserine (PS)—were identified from P. marinus extracts. Four neutral lipid classes—triacylglycerol (TAG), steryl ester (SE), cholesterol (CHO), and fatty alcohol—were distinguished. TLC/FID analysis of meront lipids showed that the weight percentages of PC, PE, CL, SM, PS/PI, TAG, SE, and CHO were 21, 10.7, 4, 2.3, 4.3, 48.7, 7.8, and 1.2%, respectively. HPLC and HPTLC analyses revealed the presence of two SM and PS isomers in P. marinus extracts. Perkinsus marinus effectively incorporated FL PC acquired from the medium and metabolized it to various components (i.e., free fatty acid, monoacylglycerol, diacylglycerol, TAG, PE, and CL). Uptake and interconversion of FL PC in P. marinus meronts increased with time. After 48 h the total uptake of fluorescence (FL) was 28.9% of the FL PC added to the medium, and 43% of the incorporated FL resided in TAG.     

Blends of polycarbonate with poly(methyl methacrylate): Miscibility,phase continuity,and interfacial adhesion

Dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) concurrently show that polycarbonate (PC)/poly(methyl methacrylate) (PMMA) blends have a two-phase structure. The differences between the T_gs of parent polymers and the T_gs of conjugate phases, determined by both DMTA and DSC, indicate a limited miscibility of components and allow the approximate composition of conjugate phases to be calculated. The Flory-Huggins interaction parameter calculated by using these data assumes values about 0.035 ± 0.010. Phase inversion occurs in an interval close to the 50/50 composition, though the molar masses and melt viscosities of the polymers were rather different. Partial miscibility of components ensures interfacial adhesion capable of sustaining the stress transfer between phases up to fracture. Yield stress of the blends is very close to values foreseen by the rule of mixtures. A specific feature of the blends studied is that the addition of 10 to 20 vol% of PMMA to PC increases the strain at break and work to fracture, which are rather low for the PC used. The enhanced capability of the blends to absorb mechanical energy is probably linked to plastic deformation of the dispersed PMMA.     

Rheological behavior of blends of poly(methyl methacrylate) (PMMA) and poly(acrylonitrile-stat-styrene)-graft-polybutadiene (ABS)

The rheological behavior of blends of poly(methyl methacrylate) (PMMA) and poly(acrylonitrile-stat-styrene)-graft-polybutadiene (ABS) was investigated using a cone-and-plate rheometer. The rheological properties measured were shear stress (σ₁₂), viscosity (η), and first normal stress difference (N₁) as functions of shear rate (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma$ \end{document}) in steady shearing flow, and storage modulus (G′) and loss modulus (G″) as functions of frequency (ω) in oscillatory shearing flow. It has been found that the rheological behavior of blends of ABS and PMMA was very similar to that of blends of poly(styrene-stat-acrylonitrile) (SAN) and PMMA, in that N₁ in logarithmic plots of N₁ versus σ₁₂, and G′ in logarithmic plots of G′ versus G″, vary regularly with blend composition. This has led us to conclude that the rubber particles that are grafted on an SAN resinous matrix in ABS resin plays only a minor role in influencing the compatibility of ABS/PMMA blends, and that the SAN chains attached to the surface of rubber particles, and the SAN matrix phase, play a major role in compatibilizing ABS resin with PMMA.     

The antioxidant effects of phospholipids on perilla oil

Antioxidant effect of phospholipids on the oxidation of refined perilla oil (PO;α-18:3, 54.5%; 16:0, 7.2%; 18:0, 2.6%; 18:1, 18.6%; 18:2, 15.5%), tocopherol-free (POF) and tocopherol-enriched (POR) perilla oil were investigated by measuring weight-gains and by the oven test at 37°C. The oxidative stability of PO was especially increased by additions of phosphatidylethanolamine (PE) and phosphatidylserine (PS), but phosphatidylcholine (PC) scarcely showed an antioxidant effect. The oxidative stability of POF was markedly low, and none of the phospholipids (PC, PE, PS) showed an antioxidant effect on the oxidation of POF. The stability of POR was lower than that of PO regardless of its higher tocopherol contents. However, the oxidation of POR was significantly suppressed by additions of PE and PS, as was observed with PO. PC showed a small antioxidant effect on the oxidation of POR. Therefore, it seems that the antioxidant effects of phospholipids, especially of PE and PS, was due to the presence of tocopherols in the perilla oil.     

Rapid separation of the major phospholipid classes on a single aminopropyl cartridge

A rapid method for the separation of the individual phospholipid classes phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI) by a single solid-phase extraction was developed. PC, PE, PS and PI were sequentially eluted from aminopropyl bonded silica with acetonitrile/n-propanol (2∶1, vol/vol), methanol, isopropanol/methanolic HCl (4∶1, vol/vol) and methanol/methanolic HCl (9∶1, vol/vol). Standard recoveries were over 95% for PC and PE and over 85% for PS and PI with undistorted fatty acid composition. The separation of complex lipid mixtures on aminopropyl minicolumns can be refined to the level of individual phospholipid classes.     

Blends containing core–shell impact modifiers. Part 3 – Effects of temperature on tensile impact behaviour

Abstract

The performances of two contrasting core–shell impact modifiers, in blends with polycarbonate (PC), poly (methyl methacrylate) (PMMA), and poly (styrene-co-acrylonitrile) (PSAN), have been evaluated using tensile impact tests at temperatures between -80 and +50°C. In both modifiers, each individual particle has a 10 nm thick outer shell of PMMA, which is grafted to the rubber phase. In the case of modifier PB, the core of the particle is a 200 nm diameter homogeneous sphere of polybutadiene, with a T _g of -86°C. Modifier PBA has a 260 nm core of PMMA, surrounded by a 20 nm inner shell of poly (butyl acrylate-co-styrene), which has a T _g of -17°C. Tensile impact tests show that the T _g of the rubber does not necessarily control the brittle–ductile transition temperature T _BD. Both the PC–PB and PC–PBA blends exhibit some ductility at -80°C, although neither blend is as tough as plain PC at any temperature. The blend of PB with PMMA shows a modest increase in toughness above -40°C and there is a similar but rather larger increase in the toughness of the PMMA–PBA above -20°C. In PSAN blends, the PBA modifier is the more effective toughening agent ahove 0°C. It is concluded that these differences originate from differences in the balance between shear yielding and crazing in the matrix polymer, and in the ability of cavitated rubber particles to prevent crazes from turning into cracks. In PMMA and PSAN blends, the PBA modifier is the more effective toughening agent at 23°C because of its rigid core, which enables stable rubber fibrils both to form and to contribute to local strain hardening, thereby stabilising the yield zone.     

Crystallization kinetics of PE‐b‐isotactic PMMA diblock copolymer synthesized using SiMe2(Ind)2ZrMe2 and MAO cocatalyst

Polyethylene‐b‐poly(methyl methacrylate) (PE‐b‐PMMA) diblock copolymer has important interfacial applications. Hence, a PE‐b‐isotactic PMMA diblock copolymer was synthesized using SiMe₂(Ind)₂ZrMe₂ and MAO cocatalyst. The polymerization mechanism and the origin of PMMA isotacticity were duly explained. An appropriate nonisothermal Avrami‐Erofeev crystallization model was developed to compare the crystallization kinetics of the above copolymer with that of a PE homopolymer. For both polymers, the model well matched the entire differential scanning calorimeter crystallinity profile, notably for a single Avrami‐Erofeev index, and predicted cylindrical crystal growth. This model particularly overcomes the limitations of the published nonisothermal crystallization models, and provides interesting insight into PE crystallization. The PMMA block significantly decreased the heats of crystallization and fusion, % crystallinity, and the relative crystallization function; increased the nonisothermal crystallization rate constant; and introduced minimal dilution effect whereas the PE block formed a continuous or percolated phase. This study correlates catalyst structure, copolymer block tacticity, and PE nonisothermal crystallization and melting behavior. © 2012 American Institute of Chemical Engineers AIChE J, 59: 200–214, 2013     

Lipids rich in phosphatidylethanolamine from natural gas-utilizing bacteria reduce plasma cholesterol and classes of phospholipids: A comparison with soybean oil

We compared the effects of three different high-lipid diets on plasma lipoproteins and phospholipids in mink (Mustela vison). The 18 mink studied were fed one of the three diets during a 25-d period in a parallel group design. The compared diets had 0,17, and 67% extracted lipids from natural gas-utilizing bacteria (LNGB), which were rich in PE. The group with 0% LNGB was fed a diet for which the lipid content was 100% soybean oil. The total cholesterol, LDL cholesterol, and HDL cholesterol of animals consuming a diet with 67% LNGB (67LNGB-diet), were significantly lowered by 35, 49, and 29%, respectively, and unesterified cholesterol increased by 17% compared with the animals fed a diet of 100% lipids from soybean oil (SB-diet). In addition, the ratio of LDL cholesterol to HDL cholesterol was 27% lower in mink fed the 67LNGB-diet than those fed the SB-diet. When the mink were fed the 67LNGB-diet, plasma PC, total phospholipids, lysoPC, and PI were lowered significantly compared with the mink fed a SB-diet. Plasma total cholesterol was correlated with total phospholipids as well as with PC (R=0.8, P<0.001). A significantly higher fecal excretion of unesterified cholesterol, cholesteryl ester, PC, lysoPC, and PE was observed in the 67LNGB-fed mink compared with the SB-fed mink. We conclude that phospholipids from the 67LNGB-diet decreased plasma lipoprotein levels, the LDL/HDL cholesterol ratio, and plasma phospholipid levels, especially lysoPC and PC, compared with the highly unsaturated soybean oil. Our findings indicate that the decrease of plasma cholesterol is mainly caused by a specific mixture of phospholipids containing a high level of PE, and not by the dietary FA composition. The lack of significant differences in the level of plasma PE due to the diets indicates that most of the PE from LNGB has been converted to PC in the liver. Thus, plasma cholesterol may at least be partly regulated by phospholipid methylation from PE to PC in the liver.     

Phospholipids ofRhizobium meliloti andAgrobacterium tumefaciens: Lack of effect of Ti plasmid

We have studied the phospholipid composition ofRhizobium meliloti strains which do or do not contain the large, tumor-inducing (Ti) plasmid ofAgrobacterium tumefaciens. The major phospholipids of stationary phase cells were phosphatidylethanolamine (PE) (22%), phosphatidyl-N-methylethanolamine (22%), phosphatidylcholine (PC) (27%), phosphatidylglycerol (11.4%), and cardiolipin (11%); as average percent of lipid phosphorus. Phosphatidyl-N,N-dimethylethanolamine (3.7%) was also present. The proportions of PE were higher, and PC lower, in logarithmic phase cells. No significant differences were seen in the proportions of phospholipids in strains with or without the Ti plasmid. Qualitative examination of the phospholipids ofA. tumefaciens with or without the Ti plasmid similarly revealed no differences.