Properties and Applications of the PET Short-Cut Fibre

Abstract: The PET short-cut fibre (the fiber length less then 12 mm) is a one of the new productions which was
developing gradually from last 80th.With the development of chemical fibre machine technology, the
PET short-cut fiber has more chance to enlarge its sales volume and application rang in uninterrupted
growth way. This paper expounds PET short-cut fibre properties which can be use in different area.
Keywords: polyester fibre, ultra short fibre,characteristics，apply， papermaking, filler, flocking

1. The Significance of PET Ultra-Short Fiber Development Since the 1980s, the production technology of PET ultra-short fibers (fiber length under 12mm) has matured and was initially used in composite materials such as reinforcement and filling materials for engineering materials. With the development of PET production technology and the reduction of raw material costs, the application fields of PET ultra-short fibers have been continuously developed and have played a significant role in the paper industry. PET ultra-short fibers replace some plant fibers in papermaking, improving paper performance, expanding its uses, and aiding in forest protection.

2. Varieties and Characteristics of PET Ultra-Short Fibers 2.1 Varieties The PET division has developed three major series of PET ultra-short fiber products: papermaking fibers, composite filling fibers, and special-purpose (anti-counterfeiting) fibers. The fiber fineness ranges from 0.83dtex to 6.66dtex, and the cutting lengths can be 2mm, 4mm, 6mm, 8mm, 10mm, 12mm, etc., with colors available in ultra-white, fluorescent, and colored.

2.2 Performance Based on different usage requirements, the physical and mechanical performance requirements for PET ultra-short fibers are higher than those for conventional textile fibers. Their performance can be mainly summarized as follows: higher tensile strength and lower elongation at break, low shrinkage rate in boiling water or hot air, cutting length shorter than conventional fibers, high degree of dispersibility in other media, fiber surface characteristics, and adaptability of fiber-contained additives to special requirements.

2.2.1 High Strength and Low Elongation, and Structural Stability For PET ultra-short fibers used in papermaking, they are required to not affect or even improve the paper’s tear strength and tensile strength. They must maintain structural and dimensional stability at high temperatures. To achieve a similar appearance diameter to other papermaking fibers to increase compatibility, the fiber diameter generally ranges from 9μm to 25μm (equivalent to PET fineness from 0.83dtex to 6.67dtex). Therefore, from a physical and mechanical performance analysis, PET ultra-short fibers have special requirements different from textile fibers.

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2.2.2 Fiber Length Similar to Natural Fibers

The natural raw materials used in the paper industry are mostly plant fibers, as well as some animal fibers and mineral fibers. The length and width of plant fibers are shown in Table 1.

Table 1 A Glimpse of Plant Fiber Length and Width

Fiber Variety	Average Fiber Length (mm)	Average Fiber Width (μm)
Softwood Fibers	1.34～4.08	36.3～66.6
Hardwood Fibers	0.73～1.21	13.2～24.1
Bamboo Fibers	1.10～2.00	12.0～16.2
Grass Fibers	0.83～1.64	8.1～27.7
Bast and Seed Fibers	2.26～18.42	12.9～28.6

For PET ultra-short fibers used in the paper industry, their appearance characteristics need to be similar to natural fibers, especially in terms of fiber length.

In the early 1980s, the models and manufacturing technology of cutting machines were relatively backward, making it very difficult to achieve a fiber cutting length less than 6mm, and it was almost impossible with gear wheel cutting machines. To adapt to the continuous production of ultra-short fiber cutting and the requirements of cutting quality, several famous foreign chemical fiber equipment manufacturers dedicated themselves to researching specialized cutting machines. Notably, the special cutting machine developed by the German company Neumag features a slant disc press cutting press disc and a special blade disc frame design, which can cut fiber lengths shorter than 3mm. The cutting machine adjusts the number of blades on the blade disc to cut ultra-short fibers of different lengths; the specially designed blade shape and steel can ensure that there is no melt adhesion at the broken ends of the fibers; and according to different fiber moisture content and fiber diameter, total fineness, the time of blade use is judged and controlled.

2.2.3 Dispersibility in Media

For PET ultra-short fibers, the most critical technology according to the application field is that the fibers must have good dispersibility in other solvents, which is almost the opposite of textile fibers. In other media, PET ultra-short fibers must have very good solubility and dispersibility. Compared to other synthetic fibers, PET has a higher specific gravity than water and is very prone to sedimentation without mechanical stirring. Therefore, a special dispersant must be applied to the surface of the fibers to make the fibers repel each other in other media, achieving uniform dispersion. Different dispersants or adjustments to the ratio and amount of dispersant spraying can be chosen according to different media.

In production, controlling the moisture content of finished ultra-short fibers to around 10% is beneficial to the dispersibility of the fibers in aqueous media.

To meet the quality requirements of printing and writing paper, the appearance quality of the fibers is particularly important. Especially for thin paper, even if only two fibers are stuck together, it may affect the quality of the paper. The appearance quality requirements for fibers are extremely harsh: 10g of ultra-short fibers dissolved in a 1m³ water pool, after dehydration, there should be no completely parallel stuck fibers or deeply dyed spots at 0mg/100g.

Therefore, in the fiber production process, it is necessary to ensure uniform cooling and molding conditions to ensure the uniform internal and appearance quality of the fibers.

2.2.4 Surface Characteristics

Conventional textile fibers use surface-active agents in the production process to treat the fiber surface, adjusting the composition and ratio of the components to achieve anti-static, regulate fiber-to-fiber friction, and other purposes to meet the requirements of textile processing. Since the surface treatment requirements for papermaking PET ultra-short fibers are different from those of textile fibers, traditional oiling methods and means cannot meet the requirements. At the same time, in the production process of ultra-short fibers, it is necessary to eliminate the static electricity generated by the friction between fibers and mechanical equipment to make the production stable and the cutting length consistent, reducing defects caused by un-stretched fibers. Therefore, ultra-short fibers use special surface-active agents and treatment methods different from conventional fibers. The product’s surface tension, contact angle, and friction coefficient between fibers are close to conventional papermaking materials.

2.2.5 Adaptability of Additive-Containing Ultra-Short Fibers to Special Requirements

To improve the adaptability of ultra-short fibers in various fields, it is also necessary to add special additives to the fibers according to different usage requirements, such as adding special brighteners to meet the requirements of anti-counterfeiting technology development; adding heat stabilizers to meet the requirements of high-temperature usage environments for the dimensional stability of composite materials. Chemical additives or ultra-fine physical powder additives are generally used now.

3. Application Fields of Ultra-Short Fibers

The application fields of ultra-short fibers can be roughly divided into three categories. First, they are used in the paper industry; second, they are used as reinforcing fillers for composite materials; third, they are used in flocking products.

The largest consumption of PET ultra-short fibers worldwide is in the wet papermaking industry, from ordinary paper to high-grade and special paper, almost all have traces of PET ultra-short fibers. The use of paper containing PET ultra-short fibers is very broad, including military supplies, interior decoration materials, filter materials, electrical materials, etc.

3.1 Papermaking

According to the amount and requirements of ultra-short fibers added in paper, their uses can be roughly divided into three categories. First, for paper recycling and regeneration; second, to improve the performance of paper; third, for special purposes (see Table 2). Adding 3% to 5% PET ultra-short fibers to the pulp can effectively enhance the paper’s tensile strength and tear strength, reduce the basic weight of the paper, effectively improve water resistance, increase paper drying speed, and improve production capacity per unit, thereby reducing production costs. In Europe, paper reuse has been legislated, and adding PET ultra-short fibers can improve the quality of recycled paper, while adding PET ultra-short fibers to the pulp can provide an effective way to save forest resources.

Continuing from where we left off, here is the translation for the remaining parts of the document:

Table 2: Main Applications of Ultra-Short Fibers in the Paper Industry

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Category	Paper Variety	Purpose and Objective	Features	Addition Amount
Recycled Paper	Newsprint	After multiple uses, the paper’s strength and tear strength decrease. Adding PET ultra-short fiber solves the problem of strength and tear.	Simple addition process, energy saving, obvious effect, reduces environmental pollution	About 5%
	Writing and Printing Paper	Improve the paper’s strength and tear strength, enhance writing ability.	Same as above, replace wood pulp, protect forest resources	5%-10%
Improve Paper Performance	Photo Base Paper	Enhance paper’s solvent resistance and dimensional stability in solvents.	PET has high acid and alkali resistance	20%
	Map Paper	Improve paper’s folding endurance and strength in different environments.	PET is hydrophobic, also has high tensile strength and modulus, water-resistant, fold-resistant	50% and above
	Food Packaging Paper	Improve tear strength and oil and temperature resistance.	Not easily contaminated, can be disinfected at high temperatures	20%
	Industrial Packaging Paper	Improve tear strength and water resistance, used for powder and granular packaging.	Water-resistant, enhance strength	20%
	Ultra-thin Paper	Photo-sensitive typing paper, infrared scanning paper, etc.	Ultra-fine PET fibers can improve printing and printing resolution	50% and above
	Large Format Advertising Paper	Large format poster paper with surface plastic coating and back glue, improve water resistance and tear strength.	Good affinity with coatings	More than 20%
	Currency Paper	For currency, securities, certificates, improve dirt resistance, waterproof and strength.	Can embed special materials in paper, increase manufacturing difficulty	10%
	Filter Paper	For automotive engine oil, fuel filtration, food processing filtration, medical filtration.	Oil-resistant, has strong toughness and strength, can withstand certain temperatures	30%
Special Purposes	Anti-counterfeiting Paper	Glows under special light sources.	Added fluorescent agents	5%
	Electrical Material Paper	Insulation paper.	Contains special additives	5%
	Anti-photocopying Paper	Can prevent photocopying for certificates, etc.	Contains special additives	5%
	Wallpaper	Washable, stain-resistant, can be embossed.	Colored, low melting temperature	30%-40%

3.2 Composite Material Fillers

The earliest ultra-short fibers were mainly glass fibers used in building materials and insulation materials. At the end of the 1980s, the application fields of composite materials have developed greatly, and higher requirements were put forward for the fillers in composite materials, especially for PET ultra-short fibers.

Some advantages and characteristics of PET make it play a certain role in the construction industry. It is mainly used to strengthen the impact strength of concrete. For example, adding ultra-short PET at a ratio of 0.95kg/m³ to concrete can increase its impact strength from the original 47.9Pa to 91.0Pa, almost doubling it.

Used as a filler in indoor sound insulation materials. Adding a small amount of ultra-short fibers to foam materials can increase a certain surface wear strength, and also form a micro-velvet on the surface of the filler to achieve a certain sound insulation effect.

Used as an additive for the film strength of coatings. In arid and cold regions, coatings are very prone to cracking when used. Adding about 1%-2% ultra-short fibers can effectively prevent the cracking of coatings.

Used as an additive for the paint below the waterline of sailing ships. During film formation, it makes the surface have fine undulations, which can prevent and reduce the adhesion of marine shellfish to the hull.

Used as a reinforcing material for rubber materials, to improve the weft strength of conveyor belts and V-belts. As a reinforcing material in plastics, to reduce cracking caused by temperature changes, etc.

References
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[3] Gu Shuying, Application of Synthetic Fibers in Concrete, Synthetic Fibers, 2000 (1)
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[5] Xiao Changfa, Fiber Composite Materials, Beijing: China Petrochemical Press, 1995