M. D. de Castellar

Abrasion Kinetics of Wool and Blended Fabrics

The abrasion resistance of different wool and blended fabrics is measured with the Martindale wear and abrasion tester, the abrasion kinetics is identified by the shape of the mass loss curve versus abrasion cycles up to yarn breakage. A concave kinetic curve shows a low initial weight loss rate, which continues to increase throughout the process up to the end. A convex kinetic curve begins with a high initial weight loss rate, which continues to decrease throughout the process. The third kinetic curve shows an almost linear relationship between mass loss and abrasion cycles up to yarn breakage. Due to the long time required for the abrasion test to yarn breakage, a simplified method is used based on the determination of mass loss up to 5000 abrasion cycles. The initial mass loss rate and the mean value of this rate throughout the 5000 abrasion cycles (i.e., the mean abrasion gradient) seem to be good estimates of the surface and structural abrasion degradation of the fabrics, and they show a strong relationship with the structural parameters of the fabrics.

Elastic Recovery and Inverse Relaxation of Polyester Staple Fiber Rotor Spun Yarns

We have studied the elastic recovery and inverse relaxation phenomena of polyester staple fiber rotor spun yarns. Better fiber orientation obtained with a drawing passage before spinning results in higher permanent deformation and lower delayed elastic recovery of the yarn. Yarn twist has little influence on elastic characteristics. The stress produced in the yarn when strained at 10% is higher when fibers are straighter and lower when twist increases. The inverse relaxation effect increases with the level of orientation of the fibers in the yarn.

Frictional properties and wear of a molybdenum coating and a bronze (Cu-10%Sn) with friction modifier fillers

Abstract A new manufacturing process and a new family of composite materials (bronze matrix + friction modifiers) for lubricated tribological systems, such as synchronizer rings in manual gear boxes, has been developed. The research has provided a better understanding of lubricating oil film formation and how to stabilize it by a suitable surface chemistry and morphology, as well as the ability to produce such a surface by means of non flat powder-metallurgical (P/M) composite coatings. Commonly used synchronizers are of two types: forged brass and sintered steel with molybdenum coating. Brass synchronizers work very well when new but degrade with use. Molybdenum coatings are produced by a high cost plasma spraying. The new bronze based friction materials have reached the performance level of molybdenum coating in tribometer measurements. The tribological behaviour of the Mo and bronze ring types was characterized in lubricated conditions (temperature: - 10°C to 120°C). XPS and SEM/EDX analysis allowed to verify tribochemical reactions taking place during the working process.

Viscoelastic modeling of natural and synthetic textile yarns

Viscoelastic models were employed to analyze the stress–strain behavior of cotton, acrylic, and polyester yarns. The potential model and the modified Maxwell model gave the best fits as regards the stress–strain behavior of these yarns. The results of the potential model resembled those of the modified Maxwell model with an infinite relaxation time. The potential model is suitable for explaining the rearrangement undergone by the yarns when no slippage between fibers under strain occurs. When slippage occurs, Maxwell models are able to explain the stress–strain behavior of the yarns.

Cracks in Sorel's cement polishing bricks as a result of magnesium oxychloride carbonatation

A magnesium oxychloride polishing brick showed, after five months, both original planes bent towards the same side and two perpendicular systems of cracks. A powdered sample of the crust treated with distilled water, revealed two sedimentary layers. Brucite, oxychloride form 3, chlorocarbonate and traces of form 5 were identified in the lower level. Periclase, F5 and brucite were identified in the upper level. The association of F3 with the basic chlorocarbonate suggests that the carbonatation takes place on this form. This carbonatation implies an increase volume producing enough stress to provoke the observed cracks. The CaO impurities yield aragonite, so this is formed simultaneously with chlorocarbonate due to the atmospheric CO2 and magnesium ions act as inhibitors of the calcite formation.

Effect of Finishing on Woven Fabric Structure and Compressional and Cyclic Multiaxial Strain Properties

Twenty-three woolen, mixed and worsted woven fabrics made of wool, polyester/ wool, polyester/cellulosic and waste fibers underwent four different finishing treatments. The effect of the finishing on gray goods was studied by comparing the structural parameters and the results obtained by compressive and cyclic multiaxial strain testing. It was observed that finishing lead to a more fully, dimensionally stable and more relaxed fabric structure. By comparing the results obtained from finished fabrics it was possible to distinguish between the different groups of finished fabrics: Pure wool fabrics, non-pure wool fabrics, woolen fabrics made of warp worsted yarns (mixed fabrics) and pure worsted fabrics. The measured structural parameters were fabric density, thickness and mass per square meter, Eurotex and image analysis cover factors, air permeability and sonic velocity. The results given by compressional testing were compressibility, the Onions compressive index and Kawabatas linearity of compression. The results of the cyclic multiaxial strain testing were initial deformation, relaxation and creep indexes and bagginess after five deformation cycles.

Shrinkproofing Untreated Wool with Hercosett/Uvitex NFW/Hydrogen Peroxide Systems—Physicochemical Properties of These Systems

We have studied the physicochemical properties of dispersion systems made with a cationic Hercosett resin, the anionic optical brightener agent Uvitex NFW, and the oxidative agent hydrogen peroxide. We have also investigated the application of these systems to untreated knitted wool samples to obtain improved whiteness and shrink proofing properties, and the damage to the physicochemical properties of the keratin fibers.

Apparent Loss of Twist in Blended Polyester-Cotton Ring and Rotor Spun Yarns

We have studied the extractive nozzle effect on apparent loss of twist in acrylic staple rotor spun yams [2] through a factorial scheme with four factors: two quantitative (yarn linear density at three levels and yam twist multiplier at five levels) and two qualitative (three exit nozzles types and four rotor types). Our results showed that both rotor type and nozzle type exert a significant influence on the apparent loss of twist, called also &dquo;residual twist&dquo; [ 1 ]. This last parameter tends to increase, when the exit nozzle produces a false twist effect in the yarn and tends to diminish when yam friction against the rotor is increased. It also depends on yarn linear density and yam twist multiplier. We experimented further with 40 and 60 tex poly-. ester/cotton blended (70%, 30% and 50%, 50%) rotor spun yams. Yarn preparation was as described in reference 3 and 24 yarns were obtained: 8 ring spun yams, 12 open-end spun yarns (sawtooth shaped wire clothing in the opening roller) and 4 open-end spun yams (pinned wire clothing in the opening roller). The apparent loss of twist was determined in the same way [4] as in reference 2. Results are summarized in Table I and twist values expressed as twist multipliers (to cm-’ tex). We can verify that eight ring spun yarns show the existence of small positive and negative differences for the apparent loss of twist. This allows us to formulate the hypothesis that a true apparent loss of twist does not appear in ring spun yarns and that differences

OPTIMIZING HERCOSETT/OPTICAL BRIGHTENER AGENT/HYDROGEN PEROXIDE SYSTEMS APPLIED TO UNTREATED WOOL FOR SHRINKPROOFING

We have studied the application on untreated wool fibers of different aqueous dispersion systems made with Hercosett, a cationic resin; three commercial anionic optical brightener agents (OBA), Uvitex CF-200, Blankophor BA Liq. B, and Uvitex NFW; and the oxidative agent hydrogen peroxide to improve both whiteness and shrink-proofing properties with less damage to the keratinic structure. Treatment times and temperatures were optimized using the central composite rotatable design of Box and Hunter and, in all cases, a weight ratio of Hercosett/OBA that produced better shrink-proofing. Results obtained for each OBA were also compared to determine optimum application.

Twist and Linear Density Coefficient of Variation-Length Curves of Polyester/Cotton Yarns Spun by Different Processes

The coefficients of variation-length curves for yarn twist and linear density have been determined for polyester/cotton yarns spun by ring, rotor, and friction processes as a function of blend proportion, yarn twist, and yarn linear density. The influence of each of these parameters on twist and linear density irregularity is described according to the spinning process. The coefficients of variation length curves can be mathematically represented with sufficient accuracy by a polynomial expression including first-and second-order terms.