Tensile Fracture and Failure Behavior of Thermoplastic Starch with Unidirectional and Cross‐Ply Flax Fiber Reinforcements

Thermoplastic starch (MaterBi®) based composites containing flax fibers in unidirectional and crossed‐ply arrangements were produced by hot pressing using the film stacking method. The flax content was varied in three steps, viz. 20, 40 and 60 wt.‐%. Static tensile mechanical properties (stiffness and strength) of the composites were determined on dumbbell specimens. During their loading the acoustic emission (AE) was recorded. Burst type AE signal characteristics (amplitude, width) were traced to the failure mechanisms and supported by fractographic inspection. The mechanical response and failure mode of the composites strongly depended on the flax content and the flax fiber lay‐up. It was established that the tensile strength increases until 40 wt.‐% flax fiber content but stays almost constant above this value. In the case of 40 wt.‐% unidirectional fiber reinforcement, the tensile strength of the composite was 3 times greater than that of the pure starch matrix. The flax fiber reinforcement increased the tensile modulus of the pure starch by several orders of amplitude.

SEM picture of the fracture surface of a composite with UD flax reinforcement.     

Effects of thermal and mechanical fatigue on flexural strength of G40-600/PMR-15 cross-ply laminates

The effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates with ply orientations of (0₂, 90₂)_2s and (90₂, 0₂)_2s are examined. The relative improtance of shear and tensile stresses is examined by varying the span-to-depth ratios of flexural test specimens from 8 to 45 Acoustic emission singals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine speciments for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, for regardless of ply orientation, span-to-depth ratio, or previous exposure of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0° ply of specimens with high span-to-depth ratios. Because of the complex failure modes, the flexural test results represent the “apparent” strengths rather than the true flexural or shear strenghts for these cross-ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strins during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32–260°C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (?85 to 85°C, 500 cycles). Mechanical cycling (0–50% of the flexural strength, 100 cycles) has a similar effect, except that acoustic events are reduced only at strains less than the maximum strain applied during flexural fatigue. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Jet-cooked starch-oil composite in polyurethane foams

A new jet-cooked starch—oil composite has been blended with a polyester polyol and then reacted with isocyanate to give a polyurethane foam. Infrared spectroscopy and microscopy have been used to examine the resultant products. Infrared spectra have shown the products contain the urethane structures and light and electron microscopy have shown the differences in the cell wall structures and networks of the foams when compared to the control foams. Inclusion of the starch—oil composite in the formulation resulted in increased viscosity of the reaction mixture as well as a more irregular cellular structure and a rougher texture of the cured foam. Larger cells were more abundant and there was more evidence of tearing during expansion. The scanning electron photomicrographs show the open-cell structure of both the control and blended foams and their reticular network, which is more uniform in the control. This examination provides insight into the foaming process and provides information to make the necessary adjustments for acquiring the desired polymeric product. Incorporation of the starch—oil composite in polyurethane foams provides a new dimension of possibilities for enhancing their physical, functional, and environmental properties. © 1997 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

J Appl Polym Sci 64: 1355–1361, 1997     

Permeability and material characteristics of vulcanized latex film during and following cyclic fatigue in a saline environment

The importance of stress or fatigue as a source of latex glove failure has been mentioned in several recent studies, but little work has been done to examine the underlying mechanism of these failures. The present work was undertaken to develop techniques for very early detection of structural changes in glove barriers. This was accomplished by monitoring the ion permeability and electrical properties of vulcanized latex glove material during cyclic fatigue in saline. Alteration in the conductance and capacitance of the membrane during the fatigue cycle showed that catastrophic failure of the material was preceded by deviation in the conductance of the membrane 8–10 min before rupture of the material. Disruption of the material coincided with capacitive “discharge” of and ion transport across the membrane. Follow-up examination by optical (100×) and scanning electron microscopy (SEM) revealed failure of the original fibril network structure surrounding the latex particles. Failure corresponded to processes consistent with repeated stress and rupture of the fibrils responsible for maintaining membrane integrity. Cyclic creep-strain measurements were carried out on the latex glove material. The estimated strain during cyclic fatigue was consistent with use during normal flexing of the glove finger. The fatigue life-time of the glove material was found to be about 2 h. Based on these studies, we conclude that failure of the glove material due to hole formation is preceded by gradual thinning (and weakening) of the membrane in localized regions. This suggests that latex inhomogeneities (defects) are the ultimate cause of failure. These findings confirm the importance of stress in explaining the source of some glove material failures, especially those failures not obviously accompanied by sharp instrument or needle penetrations. The results of the fatigue study emphasize the importance of changing gloves during prolonged use. © 1997 John Wiley & Sons, Inc.

1 This article is a US government work and, as such, is in the public domain in the United States of America.

J Appl Polym Sci 64 553–566, 1997     

Predictive modeling of microcracking in carbon‐fiber/epoxy composites at cryogenic temperatures

The temperature at which microcracking occurred in symmetrical cross‐ply carbon‐fiber/epoxy composite materials was predicted with a yield‐stress‐based failure model. A fracture mechanics analysis of the in situ strength of the ply groups in a composite material was combined with a compound beam determination of thermal stress development to create the predictive model. This approach, unlike many other models, incorporated the change in the material properties with temperature with the room‐temperature properties of the laminate to predict the low‐temperature behavior of the ply groups. Dynamic mechanical analysis was used to assess microcracking at cryogenic temperatures through the observation of discontinuities in the material properties during failure. Four different material systems were studied, and the model accurately predicted the onset temperature for microcracking in three of the four cases. It was shown that the room‐temperature properties of a fiber‐reinforced polymeric composite laminate, appropriately modified to account for property variations at low temperatures, could be used to predict transverse microcracking as a response to thermal stresses at cryogenic temperatures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1104–1110, 2004     

Fracture behavior of coated/uncoated graphite-epoxy composites

The static delamination behavior of graphite/epoxy composite specimens subjected to mode I tensile opening (using UDCB

1 Uniform double cantilever beam.

specimens), and pure mode II shear loading (using ENF

2 End-notched flexural.

specimens) were studied. The graphite epoxy composites for the study were made from commercially treated fibers, with and without an electropolymerized interlayer. The mode I fracture energy (G_IC) was found to be significantly higher (more than 50 percent) for the coated fibers. However, this improvement was accompanied by a high reduction (more than 3 times) in the mode II fracture energy (G_IIC). This effect is apparently related to poor adhesion between the interlayer and the epoxy resin, which may be corrected by use of a “top layer” of appropriate composition to form chemical bonds between the phases. The fracture toughness (K_IC) of composites made with commercially treated fibers was also evaluated, using double side-notched specimens.     

Finite element analysis of plain weave composites for flexural failure

This article presents finite element analysis for flexural behavior of woven composites considering the fiber and the matrix and their interactions. Finite element model using Abaqus program is developed to predict the homogenized properties of plain‐weave T300/LTM45 composite. Initially, curved beam elements are used to model each resin‐infiltrated fiber bundle. Geometrically, nonlinear analyses of the model with periodic boundary conditions are carried out to obtain effective in‐plane and bending properties of the composite. Statistical analysis is presented to study the stiffness variability. The flexural failure of a single‐ply composite is estimated based on the homogenized material properties, and is compared with previously published data. The model is able to correct the significant errors in the stiffnesses of the composite and captures the failure behavior accurately. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Synthesis of phosphorus-containing wofatit cation exchangers and their affinity toward selected cations

A number of solid Cationits have been prepared derived from Wofatit

1 Trademark, VEB Chemiekombinat Bitterfield.

gel and canal structures: styrene/DVB, chloromethylated ST/DVB, and acrylic acid/DVB copolymers. To functionalize the copolymers, PCl₃/AlCl₃ and dialkyl phosphites or trialkyl phosphites were used. The influence of the polymer matrix structure and the chemical structure of the functional groups of obtained Ionits on their affinity toward 23 metallic cations in acidic media has been investigated using the conductivity method. To obtain comparison data, commercial “Wofatit”–sulfonic and–carboxylic Cationits, have been tested under identical conditions.     

The STOBBE Condensation with Pyrrolyl Aldehydes – a synthesis of indole derivatives

The condensation of pyrrolyl-2-aldehyde or 1-methyl-pyrrolyl-2-aldehyde with dimethyl succinate, using sodium hydride as condensing agent, gave predominantly the halfesters 1a and 1c respectively. Their structure and (E)-configuration

1 i. e., pyrrol ring and COOCH₃ group are in trans position. This nomenclature follows the IUPAC 1968 Tentative Rules, Section E, Fundamental Stereochemistry, J. org. Chemistry 35 , 2849 (1970).

were confirmed by their cyclisation to the corresponding indole derivatives 2a–h .     

Photochemical and thermal stability of amaranth (FD&C red no. 2) in aqueous media

The decomposition of the formerly

1 This dye was delisted by the U. S. Food and Drug Administration in 1976, and has not been legally used in the U. S. in foods, drugs, or cosmetics since that date.

used food and pharmaceutical dye amaranth (FD&C Red No. 2) in water was studied under a variety of conditions. A matter of some concern is that one of the decomposition products is α-naphthylamine, a known carcinogen.     

Synthesis of phosphorus-containing polymers with potential bioactivity

Phosphorylation of poly(N-vinyl pyrrolidone-co-vinyl amine) and poly(N-vinyl pyrrolidone-co-glycidylcrotonate

1 Systematic name: (2,3-Epoxypropyl)crotonate.

) is realized by Atherton-Todd and Fields-Kabachnik reactions and by the means of direct interaction with phosphorus trichloride and phosphorus trichloride oxide. The composition and structure of the isolated final products was proved by NMR (¹H and ³¹P), IR spectroscopy and elemental analysis.     

Low dielectric,fluorinated polyimide copolymers

Copolymers of fluorinated polyimides and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) have been prepared as films and composite laminates. The addition of BPDA was used as a means to achieve insolubility, making the polymers suitable as aircraft matrix resins. Glass transition temperatures, thermooxidative stabilities, and tensile strengths were increased with increasing BPDA content in the copolymers. Although the addition of BPDA did increase the UV cutoff and decrease the percent transmission slightly, the optical transparency of the polymers was still excellent. Dielectric constants of the copolyimide films ranged from 2.6 to 2.9. Astroquartz II laminates made with these resins had dielectric constant of 3.3–3.4. Flexural strength on unidirectional specimens were in the 1.24–1.41 GPa range and flexural moduli were 41 GPa. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Gel permeation chromatography: Physical characterization and chromatographic properties of porasil

Porasil

1 Porasil is the Water Associates registered trademark for a powdered porous silica chromatographic substrate.

porous silica has been characterized by the methods of gas adsorption–desorption isotherms, mercury porosimetry, and electron microscopy. The pore structure has been shown to be quite heterogeneous, particularly at the surface of the particles. From the same sample of Porasil, columns were packed and calibrated in a gel permeation chromatograph. The availability of high molecular weight fractions of polystyrene allowed the exclusion limit of these materials to be determined for the first time. The heterogeneous pore structure did not seem to affect the effectiveness of these materials for macromolecular separation.     

Properties of standard materials for reflection

This article gives a short survey of some literature on the calibration, suitability, properties, and use of various materials which are used as standards of reflectance. The classical ultimate reference standard, smoked magnesium oxide, is discussed briefly, and information is given on the properties of materials presently used: BaSO₄, Russian opal glasses, ceramic tiles, and Halon.

1 Halon is a registered trade name of the Allied Chemical Corporation.

The suitability of these materials for use as transfer standards or working standards is discussed.     

Effect of chain microstructure on modulus of ethylene–α-olefin copolymers

A family of copolymers of ethylene and α-olefin resins with homogeneous branching distribution, which behaves as elastomers at high short-chain branching levels and acts as typical thermoplastics at low short-chain branching levels, is now available. Control of this broad range of properties stems from the ability to control the molecular architecture more effectively using Dow's INSITE

1 Trademark of The Dow Chemical Co.

technology than in the past. Due to the unique combination of narrow short-chain branching distribution (SCBD) and narrow molecular weight distribution (MWD), these resins provide a unique opportunity to model structure/property relationships in branched ethylene-α-olefin copolymers. The modulus in branched ethylene-α-olefin copolymers with aliphatic branches is shown to be primarily dictated by crystallinity. It is shown that the branch distribution and the branch type have an insignificant effect on the modulus of ethylene copolymers containing aliphatic branches at a given crystallinity. Modulus data have been successfully modeled in such systems using a lamellar fiber-reinforced amorphous matrix composite model. Switching from aliphatic branches to cyclic branches significantly affected the modulus at similar crystallinities. © 1994 John Wiley & Sons, Inc.     

Temperature gradients in the channels of a single‐screw extruder

We used a temperature‐sensitive fluorescent dye, perylene, to monitor the true resin temperature during extrusion of polycarbonate. The measurement involved doping polycarbonate with perylene and detecting fluorescence with an optical sensor that accesses a standard instrumentation port on a barrel of a single‐screw extruder. The sensor's confocal optics design permits fluorescence intensity measurements as a function of position. Using a previously established calibration function, temperature and temperature gradients were obtained from the measured fluorescence. Because the origin of the measurement is the fluorescent dye molecule that is soluble in the resin, this method allows temperature measurement of the polymer without interference from the surrounding metal parts. With the sensor looking over the screw, temperature profiles from the barrel wall to the core of the screw were obtained as a function of screw speed, screw design and resin melt flow rate. Polym. Eng. Sci. 44:2148–2157, 2004. © 2004 Society of Plastics Engineers.

1 This paper is a contribution from the National Institute of Standards and Technology, and, thus, is not subject to copyright in the United States.

     

Glass fiber-reinforced epoxy composites

Glass fiber-reinforced epoxy composites were prepared from the matrix resins tetraglycidyl diaminodiphenylmethane

1 Systematic name: N,N,N′,N′-Tetrakis(2,3-epoxypropyl)-4,4′-diaminodiphenylmethane.

(TGDDM) and tetraglycidyl bis(o-toluidino)-methane

2 Systematic name: N,N,N′,N′-Tetrakis(2,3-epoxypropyl)-4,4′-bis(o-toluidino)methane.

(TGMBT) using various amines like 4,4′-diaminodiphenylmethane (DDM), 4,4′-diaminodiphenylsulfone (DDS) and diethylene triamine (DETA) as curing agents. The fabricated laminates were evaluated for their mechanical and dielectrical properties and chemical resistance. The composites prepared using an epoxy fortifier (20 phr) showed significant improvement in the mechanical properties.     

Effect of fiber-matrix adhesion on the properties of short fiber reinforced ABS

The tensile strength, fracture energy, and impact strength of ABS reinforced with discontinuous crystalline fibers such as Fybex

1 Du Pont trademark.

can be controlled by manipulating fiber-matrix interfacial adhesion. In “good bonding” situations composite tensile strength, thermal expansion coefficient, and elastic moduli are significantly improved over the unfilled resin. The excellent impact strength of unreinforced ABS can be retained by lowering the fiber-matrix interfacial adhesion. This results in a corresponding reduction in the improvements in tensile and flexural strength. However, the elastic moduli and thermal expansion coefficients are relatively insensitive to changes in adhesion. Consequently, a material with high modulus (>500,000 psi), high Izod impact resistance (7.0 ft-lb/in.), and low expansion coefficient (3.0 × 10^?5 in./in./°F) can be obtained. A material with this unique combination of properties should find use in large parts such as camper tops, truck grilles, and snowmobile bodies. Fiber-matrix adhesion was measured directly by an x-ray analysis technique which could be employed because of the fiber's crystallinity and unique growth habit. This independent measurement allowed a correlation between bonding and composite properties. The interfacial bond strength was manipulated by a variety of fiber coatings and resin additions.