TECHNICAL BULLETINS

MFI produces fibers in a wide variety of materials, in several different shapes, in many different sizes, and in almost any color. We have prepared this section on Fiber Properties to distinguish between them. The following table compares some of the properties in a general way, followed by definitions and by information in detail.

Specific Gravity is the weight of the material compared to an equal volume of water. The specific gravity of water is 1.00. Materials with specific gravities less than water float in water; those with specific gravities more than water sink. This property is useful in identifying the material. It is also useful in comparing the volume of filaments per pound. The lower the specific gravity, the higher the yield.

Melting Point is also useful in identifying the material. These values are typical values and actual melting points may vary by 20°F from these values. It should be kept in mind that each of these materials often soften and melt over a range of temperatures, and that the useful temperature limit of a filament is quite a bit lower than the melting point.

Tensile Modulus is a measure of the stiffness of the filament. The higher the modulus the stiffer the filament. Other names for tensile modulus are elastic modulus and Young’s modulus.

Elongation refers to how much the filament will stretch before it breaks. A significant decrease in these values indicates that the filament is deteriorating usually due to UV, high temperature oxidation, or chemical attack.

Tensile Strength refers to how hard you can pull on the filament before it breaks. A significant reduction in tensile strength indicates deterioration of the material.

Bend Recovery is a filament's ability to return to its original position after being bent. Lack of bend recovery is a common mode of brush failure.

Abrasion Resistance is a filament's ability to resist being worn away. Abrasion is another mode of brush failure.

Ovality: No filament is perfectly round. Ovality is a measure of its out of roundness. It is calculated by measuring the largest and smallest diameters at a point along a filament and dividing the largest (called the d2) by the smaller (called the d1 ). Ovality generally increases with filament diameter. Certain colors and additives may affect ovality.

Set Resistance refers to a filament's ability to straighten completely after being moderately flexed for a long period. This differs from Bend Recovery which is a more severe bending for shorter periods.

Water Absorption and Retention of Stiffness in Water refer to the tendency of certain plastics to pick up and be plasticized by water. Some materials do not absorb water.

Sunlight, UV Light will result in the degradation of some polymers.

High Temperatures will cause some materials to degrade well below their melting points.

General Chemical Resistance refers to the ability of filaments to retain their important physical properties when exposed to certain chemicals. Ask about our Technical Bulletin on Chemical and Solvent Resistance.

Many polymers will become brittle from oxidation by prolonged exposure to ultraviolet light. For example, if unprotected small diameter polypropylene is left exposed to the sun it can lose half its elongation (flexibility) in less than four weeks. The resistance of polymer fibers to UV light may be increased by the addition of carbon black. Carbon black works by absorbing the UV radiation before it can cause damage to the chemical bonds in the plastic. It offers the advantages of a high level of protection and small cost. Other pigments have much less protective effect and may increase degradation of the fibers by UV light.

After this year long test, the unprotected Prostran^® would crumble to dust when rubbed with the fingers. The black Prostran^® retained most of its properties and the tensile strength of the Wytex^® was not significantly effected.

Because of their chemical nature, most synthetic fibers do not absorb water to any appreciable extent, and as a result, their physical properties are not affected by water. Wytex^® is an exception. The chemical bonds that give Wytex^® its strength and high melting point also cause it to absorb up to 10% water. Water acts as a plasticizer in Wytex^®, allowing the molecules to move more easily. This toughens the Wytex^®, but it also reduces its stiffness. Wytex^® 6.12 absorbs less water than Wytex^® 6 or 6.6 and therefore its stiffness is less affected by water. Plyer^® and Prostran^® absorb almost no water and therefore do not lose stiffness when wet.

Tensile modulus is one of the factors that affect the stiffness of a fiber. It is the ratio of force used to stretch a fiber (stress) to the amount of stretch (strain) and is a property of the material. The higher the modulus the stiffer the fiber. A fiber with a tensile modulus of 600 kpsi will be twice as stiff as a fiber of the same size and shape with a tensile modulus of 300 kpsi. Different methods of measuring tensile modulus give different numbers. Processing, additives, heat, sunlight, chemicals, humidity, and a host of other factors all affect tensile modulus. The tensile modulus of nylon fibers such as Wytex^® 6 or 6.6 can change by a factor of 4 between 0% and 100% relative humidity. The stiffness of a fiber also depends upon its size and shape.

Most materials will break down when severely bent repeatedly. Flex fatigue failure is not very common in brushes but can occur when the wrong fiber is used or the brush is abused. Embrittlement by high temperature oxidation or sunlight is sometimes confused with flex fatigue failure. Durastran^® R (polystyrene) and Durastran^® SR (SAN) have poor flex fatigue resistance, and Prostran^® has excellent resistance. (See "High Temperature Exposure" and "Sunlight Resistance".)

Abrasion resistance is the ability of a fiber to resist wearing away when it is rubbed on a surface. There are two types of abrasion: Simple abrasion where small particles of fiber are cut off by sharp particles on the surface being brushed; and Melt abrasion where friction melts the bristle tips in high speed brushing. Factors affecting abrasion include: material type, temperature, force on the brush, abrasiveness of the surface being brushed, brush speed, brush fill, etc. In the chart and table below, the higher numbers indicate the higher relative resistance. A fiber rated 200 will last twice as long as a fiber rated 100.

Most brushes wear out from abrasion or bend recovery failure. Bend recovery failure results in the bristles becoming so bent or matted so they do not function effectively. In a properly designed brush, this typically takes a long time. Factors that influence bend recovery are severity of the bending, fiber material, how the fiber is made, length of time the fiber is bent, length of time the fiber is allowed to recover, temperature, diameter, and shape. We use three different tests to investigate some of these factors: a pinch bend recovery test that results in a very sharp bend for a few seconds, a mandrel* bend recovery test that results in a less sharp bend for a few minutes, and a set resistance test that results in a slight bend for up to several days. "Set" is the permanent bend that results from a slight bend over a long period of time.

The chart on the left shows the results of sharp bending. Wytex^®, Plyer^® and Prostran^® all show good recovery, but this amount of bending will deform any bristle and should be avoided in brush use.

The chart on the right shows the Mandrel Bend Recovery for Monahan Filaments fibers. Wytex^® and Plyer^® have bend recoveries greater than 92% and are suitable for severe applications They should be used where their higher performance justifies their higher cost. Prostran^® has adequate bend recovery for many applications and is widely used in household, janitorial and industrial brushes.

The following chart shows the resistance to taking a set. In tough scrubbing applications, however, the fiber will quickly bend permanently because of the much higher amounts of bending stress that occurs. Set problems in other products can be minimized with proper brush design and reasonable care in storage and packaging.

Many polymers will oxidize rapidly and become brittle at temperatures well below their melting or softening points. For example, nylon 6.6 melts at 495°F but will lose half its flexibility in less than two hours at 325°F, and even temperatures as low as 185°F will shorten its life. Plyer^® is highly resistant to high temperature oxidation. Plyer^® will last 100 times longer than nylon 6.6 at 325°F. The life of a fiber may be substantially increased by the addition of an anti-oxidant.

The chart at left shows the natural resistance of Plyer^® to high temperature oxidation and the ability of an antioxidant to lengthen the life of Wytex^® 6.6H. Wytex^® 6.6H is preferred in certain applications where the heat exposure is intermittent or in very aggressive applications. This test was conducted under very severe conditions. Fiber life at lower temperatures will be much longer.

The chart on the right shows the effect of anti-oxidant in polypropylene. WP-40, a polypropylene fiber containing anti-oxidant, was developed for hot wet scrubbing applications, like steel mills, where a combination of high temperatures, water and strong detergents will degrade other materials. The chart shows that WP-40 stood up more than five times longer than regular Prostran^® in this very severe test. Actual brush life will be much longer under normal usage.

INTRODUCTION

Solvent and chemical resistance refers to the ability of a fiber to retain its important physical properties. Attack may range from slight swelling and loss of stiffness to complete dissolution of the fiber. The resistance of fibers to chemicals depends not only on the type of fiber and the chemical, but concentration, temperature, time, fiber diameter, stress, etc. We have written general comments on solvent and chemical resistance, followed by a more specific table.

GENERAL COMMENTS

Wytex^®

Wytex^® nylon has excellent resistance to most substances. It is however attacked by oxidizing agents, organic acids, mineral acids, and aromatic alcohols. It has excellent resistance to hydrocarbons (such as gasoline, kerosene, and diesel fuel), oils, cleaning solutions, and alkalis. It will absorb small amounts of water, low molecular weight alcohols (e.g., methyl, ethyl, or isopropyl alcohols) and chlorinated solvents, and be plasticized by them. This will result in a temporary loss of stiffness and tensile strength and an increase in elongation. Wytex^® 6.12 shows greater resistance to dilute acids and other water soluble substances than Wytex^® 6 or Wytex^® 6.6.

Plyer^®

Plyer^® has excellent resistance to most substances. It is resistant to acids, oxidizers such as hydrogen peroxide, and most solvents. Plyer^® has excellent resistance to hydrocarbon fuels, oils, and lubricants. It is, however, attacked by strong alkalis such as concentrated solutions of sodium hydroxide (lye or caustic soda), calcium hydroxide (lime, mortar), ammonia, trisodium phosphate, or sodium carbonate (washing soda, soda ash).

Prostran^®

Prostran^® offers excellent resistance to most water soluble chemicals, including fairly strong acids, or alkalis and simple hydrocarbons. It may be attacked by oxidizing agents such as hydrogen peroxide, chlorinated solvents such as 1, 1,1-trichloroethane, and aromatic solvents such as xylene, especially at higher temperatures.

Durastran^® R

Durastran^® R resists fairly strong acids, alkalis, and most water soluble chemicals including oxidizers like hydrogen peroxide. It is readily attacked by solvents such as gasoline, lighter fluid, acetone, paint thinner, etc.

Durastran^® SR

Durastran^® SR (SR stands for solvent resistant) will resist many of the chemicals that attack Durastran^® R. Durastran^® SR is not affected by gasoline, kerosene, paint thinner, or other hydrocarbons. It is, however, attacked by aromatic hydrocarbons, ketones, esters, and chlorinated hydrocarbons.

RATINGS

S—Satisfactory—The product should give good service life when used with this chemical.

M—Marginal—Depending on temperature, concentration, exposure, expected life, etc., the product may or may not give adequate performance. Specific testing for this application is recommended, or contact us for further details.

U—Unsatisfactory—The product will deteriorate in hours to weeks when used with this chemical.

NOTES