Introduction to Fibers I

What is a fiber? Fine Fine Flexible Flexible High Aspect Ratio (length-to-width ratio) High Aspect Ratio (length-to-width ratio)

How fine is fine? To get around the ambiguity of diameter (in the case of nonround fibers) or thickness (in the case of irregular shapes) fineness is often expressed in units of linear density. To get around the ambiguity of diameter (in the case of nonround fibers) or thickness (in the case of irregular shapes) fineness is often expressed in units of linear density. In its most simple form, linear density is merely the weight of a fixed length of fiber. In its most simple form, linear density is merely the weight of a fixed length of fiber.

Systems of Measurement There are three major systems used to measure linear density, denier, tex, and decitex (or dtex). They're all equally good (or bad depending upon your point of view!), but they are not consistently used. There are three major systems used to measure linear density, denier, tex, and decitex (or dtex). They're all equally good (or bad depending upon your point of view!), but they are not consistently used. The only difference among them is the fixed length. The only difference among them is the fixed length. The oldest is denier, the accepted SI unit is decitex. The oldest is denier, the accepted SI unit is decitex.

Unit of linear Density Definition denier [1] [1] weight (grams [2] ) of a 9000 m length [2] tex [3] [3] weight (grams) of a 1000 m length decitex or dtex weight (grams) of a m length [1][1] Named after the small silver coin the denarius used as a weight standard. [2][2] With apologies to purists, weight and mass are used interchangeably—Every field has its embarrassments. [3][3] Not named for the second largest state or any of its inhabitants

A word of caution There's another thing to keep in mind when using linear density—it combines both the fineness (cross-sectional area, actually) and the mass density—more later. There's another thing to keep in mind when using linear density—it combines both the fineness (cross-sectional area, actually) and the mass density—more later.

Thought experiment Let's conduct a small 'thought experiment', suppose we take the time to unwind 1000 meters of a fiber (shape is unimportant), and we take this fiber and weigh it; suppose it weighs 1 gram. Let's conduct a small 'thought experiment', suppose we take the time to unwind 1000 meters of a fiber (shape is unimportant), and we take this fiber and weigh it; suppose it weighs 1 gram m weigh 1 gram  linear density = 1 tex 1000 m weigh 1 gram  linear density = 1 tex 9000 m would weigh 9 grams  9 denier 9000 m would weigh 9 grams  9 denier m would weigh 10 grams  10 dtex m would weigh 10 grams  10 dtex Same fiber, just different systems of measurement. Same fiber, just different systems of measurement.

= WS/L Unit System for Unit System for S tex 1000 meters/gram denier 9000 meters/gram decitex meters/gram

An example Find the linear density, in denier, of a fiber for which 500 m weigh 2 grams W = 2 g L = 500 m λ [den] = 2 g x 9000 m/g / 500 m = 36 [note, all of the units 'cancel out']

For a round fiber only Where  is the mass density of the fiber * But not all fibers are round

Flexibility Ease of bending Ease of bending What is its cause? What is its cause? Material Material Fineness Fineness Inversely proportional to the fourth power of the diameter Inversely proportional to the fourth power of the diameter So if we have a two fibers with identical composition, but Fiber A has twice the diameter of Fiber B, Fiber A is 16 times (2 4 ) less flexible than Fiber A. So if we have a two fibers with identical composition, but Fiber A has twice the diameter of Fiber B, Fiber A is 16 times (2 4 ) less flexible than Fiber A. Length Length

High Aspect Ratio How high is high? How high is high? Usually l/d > 1000 Usually l/d > 1000

Natural fibers

Manufactured fibers

What’s next? Next time we’ll look at some of the properties of the more important of these fibers Next time we’ll look at some of the properties of the more important of these fibers Chemical structure Chemical structure Affinity to moisture Affinity to moisture Strength Strength Stiffness Stiffness

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