a1 introduction

Copyright - NWI, NC State University – 1991… to date

The Nonwovens Institute

1

Introduction to Nonwoven Structures

Lecture A1

TT507: CHARACTERIZATION METHODS IN

NONWOVENS


Outline

• Nonwoven vs Conventional

• Structures and their Unique Aspects

• Materials and Product Performance

• Testing and Evaluation

• Assessment Rules and Documentation

• Basic Properties


3

What is a Nonwoven?

• An assembly of fibers or filaments held together

by bonds.

• The bonds can be imparted by mechanical,

thermal, or chemical means.


4

Conventional Fabric – A Starting Point

• Clearly defined Geometry

• Yarn bonding

Fiber to fiber friction

Fiber interweaving

• Fabric bonding

Yarn to yarn friction

Weave crimp


5

Nonwoven Structures


6

Structural Elements of a Nonwoven

Primary

Fiber Orientation Distribution

Basis Weight Uniformity

Fiber Diameter Distribution

Secondary

Pore Size and Shape

Fiber-to-Fiber cross-overs/Contacts

Surface Texture/Roughness


7

Product Assessment

• Product capability demands identification and the mapping of

those demands

• Pre-product:

Reverse Engineering

Modelling

Prototype testing

• Post-Product

Performance Evaluation

Trial Testing

Consumer feed-back

Verification of performance constancy


8

Attributes of Nonwoven Products

• Properties:

Fiber related

Orientation, diameter, weight, intrinsic, ….

Structural

Distribution, uniformity, Pore size, volume fraction, …

Bonding related

Crossover, adhesion, …

• Performance:

Traditional: Absorption, tear & wear, thermal,…

Special: Biological, electrical, acoustic, aerosol filtration. .…


9

Testing,

Evaluation and Assessment

• Standards

• Methodology

• Approaches

• DOE

• Statistical methodology

• Regulation(s) requirement(s)

• …


10

Assessment Document Content

• General description of the product;

• The list of essential characteristics:

Relevant for the intended use of the product

As foreseen by the manufacturer. and

Agreed between the manufacturer and regulator

• Methods and criteria for assessing the performance of the

product in relation to those essential characteristics

• Principles for the applicable factory production control to be

applied.


3 11

Basic Property:

Nonwoven Basis Weight

Basis weight:

Mass per Unit Area or “Weight” of Fabric

Unit: gsm , oz/yd2, etc..

𝐵𝑎𝑠𝑖𝑠 𝑊𝑒𝑖𝑔ℎ𝑡 = 𝑊𝐵 =𝑀𝑎𝑠𝑠(𝑔)

𝐿𝑒𝑛𝑔𝑡ℎ (𝑚) × 𝑊𝑖𝑑𝑡ℎ(𝑚)

x y

z


3 12

Basic Property:

Fiber Packing Arrangement

Fiber packing density:

𝜇 =𝑀/𝑉

𝜌𝑓=

𝜌𝑆𝑡𝑟

𝜌𝑓≤ 1

M/V: Fabric Mass/Volume (g)

: Fiber density (kg/m3)

: Fabric Assembly density (kg/m3)

Fiber packing density is also related to fiber volume fraction

or solid volume fraction.

What is µ for a (200x52x37.7 cm) layer of unbonded loosefill fiberglass insulation

(Ceiling R-38) with a mass of 3.45 kg (Glass=2.58 g/cm3)?

𝜇 =𝑀/𝑉

𝜌𝑓=

3.45 (𝑘𝑔)/[2×0.52×.377 𝑚3 ]

2.58×103(𝑘𝑔

𝑚3)= =0.0034

NIST reports a Str=8.8 kg/m3 for Ceiling R-38 Insulation

http://en.wikipedia.org/wiki/Glass_fiber







Thermal/Conduction & FiberGlass Packing Exercise.xlsx

Generic Fiberglass.pdf






13

Fiber Size Characterization

• Fiber diameter or fiber cross-sectional dimensions

• Linear density: fiber (or yarn) mass per unit length

• Direct system

Denier: Mass, in grams, of a 9,000 m long fiber.

Tex: Mass, in grams, of a 1,000 m long fiber.

1 dtex=10 tex: mass in grams per 10,000m of fiber.

1 denier = 9 tex = 0.9 dtex

• Indirect count system: Number of hanks per pound

Cotton, Ne: # of 840yds/lb Worsted wool, Nw: # of 560yds/lb

Woolen wool: # of 1600yds/lb Linen, lea: # of 300yds/lb

Metric: # of 1000m / 1kg Finer fibers have higher count


14

Typical Fiber Deniers

(Source: Warner, 1995)

Fiber Denier

Wool 4 to 20

Silk 1.0

Cotton 1 to 3

Synthetic 0.01 to 10,000

Typical Apparel 0.7-3

Typical industrial 3

Typical carpet 6-20


15

Denier to Fiber Diameter Relationship

Fiber Denier, per definition, is: 1𝐷𝑒𝑛𝑖𝑒𝑟 = 𝑀9000𝑚 𝐿𝑜𝑛𝑔 𝐹𝑖𝑏𝑒𝑟 𝑔

1𝐷𝑒𝑛𝑖𝑒𝑟 = 𝜌𝐹𝑖𝑏𝑒𝑟(𝑔/𝑐𝑚3) × 𝑉9000𝑚 𝐿𝑜𝑛𝑔 𝐹𝑖𝑏𝑒𝑟(𝑐𝑚3)

Assuming a fiber with circular cross section of diameter, 𝒅:

1𝐷𝑒𝑛𝑖𝑒𝑟 = 𝜌𝐹𝑖𝑏𝑒𝑟(𝑔/𝑐𝑚3) × 9 × 105 (𝑐𝑚)𝜋𝑑2

4(𝑐𝑚2)

The fiber Diameter can be derived as (Fiber Density in 𝒈/𝒄𝒎𝟑):

𝑑(𝑐𝑚) =4𝐷𝑒𝑛𝑖𝑒𝑟

9×105𝜋𝜌𝐹𝑖𝑏𝑒𝑟 or 𝑑 𝜇𝑚 =

4×103𝐷𝑒𝑛𝑖𝑒𝑟

9𝜋𝜌𝐹𝑖𝑏𝑒𝑟≈ 11.894

𝐷𝑒𝑛𝑖𝑒𝑟

𝜌𝐹𝑖𝑏𝑒𝑟

The fiber Radius is even simpler to assess based on Denier and Density:

𝑅(𝑐𝑚) =𝐷𝑒𝑛𝑖𝑒𝑟

9×105𝜋𝜌𝐹𝑖𝑏𝑒𝑟 or 𝑅(𝜇𝑚) =

103𝐷𝑒𝑛𝑖𝑒𝑟

9𝜋𝜌𝐹𝑖𝑏𝑒𝑟

d

9,000 m

Mass (g) or Denier


16

Specific Surface Area (SSA)

• The primary factor in many applications

• For solid fibers (non-porous) with circular cross-section

• Fibers with high SSA (very small diameter & very

porous) react much faster than monolithic materials:

more surface is available to react.

• Examples Grain Dust: While grain isn't typically

flammable, grain dust is explosive.

• Finely ground salt dissolves much more quickly than

coarse salt.

𝑑

𝑙

Density

Zinc Oxide

Nanowires

Zinc Oxide Nanowires

in Solar Cells


17

Fiber Linear Density Measurement

• Fiber Bundle Measurement:

Based on the mass of a sample, with a known length, L, cut in the middle of a

fiber bundle:

𝐿𝑖𝑛𝑒𝑎𝑟 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑑𝑡𝑒𝑥 =10,000 × 𝑀𝑎𝑠𝑠(𝑔)

𝐿 𝑚 × 𝑁

𝐿𝑖𝑛𝑒𝑎𝑟 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑑𝑒𝑛𝑖𝑒𝑟 =9,000 × 𝑀𝑎𝑠𝑠(𝑔)

𝐿 𝑚 × 𝑁

Where N is the number of fibers in the cut sample bundle

Useless for a single fiber with only few mm in length

L


18

Fiber Linear Density Measurement

• Single fiber weighing

Fiber at least 30mm long or longer

Cut the single fiber, measure length and weigh sample

𝐿𝑖𝑛𝑒𝑎𝑟 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑑𝑡𝑒𝑥 =10,000 × 𝑀𝑎𝑠𝑠(𝑔)

𝐿 𝑚

𝐿𝑖𝑛𝑒𝑎𝑟 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑑𝑒𝑛𝑖𝑒𝑟 =9,000 × 𝑀𝑎𝑠𝑠(𝑔)

𝐿 𝑚

• Microscopic method

With Optical Microscopy or SEM, calibrated:

• Fiber diameter distribution can be directly measured


19

Linear Density Calculations

(Denier & Tex)

• Fiber diameter and density given (known):

Calculate the cross sectional area of the fiber

Converting measured diameter from µm to cm will make it easier later on

Find the fiber density in g/cm3 (or specific gravity).

Multiply these two terms. The result’s units are g/cm! Or mass per unit

length!

Since this is a linear density, for a single cm, it must be converted to 9,000m

(Denier) or 1,000m (Tex).


20

Linear Density Calculations

(Denier & Tex)

• Fiber mass and length given (known):

Divide the fiber mass by its length.

Minimum length requirement for an accurate result.

The result’s units are g/m! Or mass per unit length!

Since this is a linear density is for a single m, it must be converted to Denier

(9,000m) or Tex (1,000m).

a1 introduction

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