What oils should be removed for polyester pre-treatment?

Introduction: The pre-treatment of polyester yarn or fabric is generally based on degreasing, because polyester will be added with spinning oil 

when spinning. So, what oils are generally used for polyester spinning oil?

I hope this article can be used as a reference for auxiliary research and development workers and dyeing and finishing pre-treatment process 

developers.

There are many types of polyester filament oils, including POY, DTY oils, conventional spinning oils, drawn silk oils, textured silk oils, and 

industrial silk oils. They can all play the role of bundling, lubrication, reducing friction coefficient, and antistatic, but they have their own special 

functions and adaptability. Even for the same type of filament, the characteristics of the required oil should be different due to different 

processing equipment and post-processing processes.

Polyester filament oils can be divided into two categories: spinning oils and finished oils. The basic properties of the oils are the same, but the 

performance requirements for spinning oils are higher than those for finished oils.

I. Basic properties of oils

1. Smoothness Smoothness, or lubricity, is essentially the friction property of the oil. It is usually expressed by the static friction coefficient (μs) 

and dynamic friction coefficient (μd) between wire and wire (F/F), wire and metal (F/M), and wire and rubber (F/R) after oiling. Generally 

speaking, after a better oil is applied to the wire, the static friction coefficient of F/F should be appropriately larger, so that the wire has good 

bundling, good winding and excellent unwinding properties. There is no special requirement for the dynamic friction coefficient of F/F, but 

during false twisting, if the wire slides, it is easy to deform. It is better for the static friction coefficient of F/M to be smaller, and the dynamic 

friction coefficient is as small as possible, which can reduce the friction between the wire and the metal, reduce hair and broken ends, reduce 

the wear of the wire on the metal, and improve the processing and weaving performance of the wire. The static and dynamic friction 

coefficients of F/R can be appropriate, because in the processing process, rubber parts are used to increase the grip of the wire. If the friction 

coefficient is too small, it is easy to slip. Smoothness is determined by the performance of each component of the oil and has a certain 

relationship with the lubrication condition. Lubrication with a high oil content (0.5% to 1.0%) is fluid lubrication. In fluid lubrication, the friction 

coefficient increases with the increase of oil viscosity and oil content. The lubrication with the lowest oil content and the smallest friction 

coefficient is critical lubrication. At high speed and high contact pressure, it is very important to maintain critical lubrication. Under critical 

lubrication conditions, in addition to the viscosity of the oil affecting the friction coefficient, the oil film strength (interface adsorption force, 

intermolecular cohesion) also has a great influence on the friction coefficient. The higher the oil film strength, the smaller the fluctuation of the 

friction coefficient.

2. Antistatic Polyester is a good insulator. When it is rubbed during processing and use, negative static electricity will be generated due to the 

accumulation of charges. Static electricity makes the silk loose and the processability deteriorates. Therefore, the fiber after oiling should have 

antistatic properties. There are usually three antistatic mechanisms: enhancing the hygroscopicity of the fiber; reducing friction; neutralizing the 

generated charge. The three mechanisms can act at the same time. The simplest method to determine the antistatic property of oil is to 

determine the resistivity of the silk strip after oiling, and the friction charge of the silk strip can also be determined.

3. Heat resistance For silk strips that need to undergo thermal processing (stretching, false twisting, etc.), the heat resistance of the oil is very 

important. Oils with poor heat resistance will decompose at high temperatures, and the physical properties of the oil will change. The 

volatilization of the oil at high temperatures reduces the amount of oil applied and pollutes the environment. The tar or oil droplets produced 

will also affect the operation. The heat resistance of the oil can be determined by the volatility reduction method, that is, the oil is placed in an 

oven at 220°C for 8 hours, and its volatility and decomposition reduction are measured.

4. Interface characteristics The oil must have certain emulsification properties. The oil emulsification is required to be stable, the surface tension 

of the emulsion is low, and the viscosity is small. It can be evenly attached to the fiber surface. If the interface characteristics are not good, even 

if other properties are very good, it cannot meet the use requirements.

Ⅱ. Use of oils

1. According to the purpose of the silk strips

Selecting oils for weaving requires good sizing properties. After sizing, the sizing film does not peel off or falls off very little during weaving. 

This requires good compatibility between the oil and the sizing material. The sizing property of the lubricant is better when the lubricant is 

mineral oil, because the viscosity of mineral oil is low, and its emulsion oil film is not only compatible with the sizing material, but also easy to 

redisperse. The oil and sizing material are replaced on the surface of the fiber, and the oil film can protect the sizing film.

The knitting silk will be directly put on the machine for warping and weaving, and will produce high-speed friction with the knitting needles. 

The requirements for smoothness, bundling and antistatic properties are all high. The oil used should have low viscosity, low friction coefficient 

and high oiling amount.

High temperature resistance should be the main feature of the oil for false twist texturing, and its smoothness can be moderate, because too 

large or too small will cause tension changes and uneven twist. In addition, the oil is required to produce less white powder and uniform 

adhesion. Uneven adhesion affects the dyeing performance of the silk.

There are many brands of oils. When using a new oil, it is best to use it in production after a small test. Improper use will affect production and 

product quality.

2. Oil dosage

The amount of oil is calculated based on the oil content (OPU) of the yarn. The OPU of conventional spinning machine weaving yarn is 

0.6%~0.7%, the OPU of knitting yarn is 0.7%~0.9%, and the OPU of stretching yarn is 0.5%~0.6%. The amount of oil applied in conventional 

spinning also depends on whether hairy yarns and broken ends are produced during stretching, because when the content of some oils is high, 

the tension of the yarn will increase, causing hairy yarns and broken ends.

The OPU of high-speed spinning varies with the processing speed of the DTY machine. The higher the processing speed, the lower the OPU 

should be (see Table 1). If POY spun by high-speed spinning is used for stretching to make stretched yarn, the amount of oil applied should be 

appropriately increased.

Relationship between the processing speed and oiling amount of DTY machine

Table

The finished oil agent applied to the deformed yarn after deformation is 2%~3% for knitting and 0.5%~1.5% for weaving. For the deformed 

yarn of water jet loom, about 0.5% of oil agent is applied to facilitate unwinding. If the warp yarn is not sized, about 1.5% of oil agent can be 

applied after adding the network.

Some special yarns, such as special-shaped yarns and colored yarns, should be 0.1%~0.2% higher in oiling amount than ordinary yarns.

3. Oil concentration

The oil concentration is restricted by several factors and should be determined by comprehensive balance. Considering the uniformity of oil 

adhesion on the yarn, the lower the oil concentration, the better, but it is easy to splash the oil, especially the oiling equipment of the tanker, 

and the splashing is more serious. Generally, the concentration of conventional spinning oil agent is 10%~15%, and the concentration of 

high-speed spinning oil agent is 8%~15%.

4. Preparation of oil

In some types of filament oil, some components are not easy to emulsify (disperse) in water. Even if they are emulsified, they exist in the form 

of condensed complex particles. The size of the condensed complex particles is mainly determined by the initial emulsification conditions, that 

is, the conditions when the oil and water come into contact.

(1) Temperature: When barreled oil is stored at low temperature, the components will be stratified. In this case, the barrel should be placed in a

 40℃ water bath or a warm room, and after the solid part is dissolved, stir it evenly before use. The water temperature during oil preparation 

varies with the performance of the oil, but is usually 20-30℃. (2) Water quality: Generally, ion exchange water can meet the requirements, but 

ion exchange water may contain silicon. After long-term use, the combination of silicon and oil is easy to clog the oiling nozzle. (3) Stirring: The 

oil needs to be stirred to be uniform when injected into the water. The shorter the contact time between oil and water, the smaller the 

condensed complex particles formed. The particles formed are small when the oil is injected into the water with the fastest stirring speed in a 

trickle. When the stirring speed is between 100 and 400 r/min, the liquid flow rate near the kettle wall is the fastest. After the oil is injected, 

continue stirring for about 30 minutes. (4) Anticorrosion of oil solution: The prepared oil will produce sediments and block the pipeline due to 

its corruption during storage and use. Bacteria (microorganisms), oxygen, nutrient sources and temperature are the conditions for corruption. 

There are two commonly used anticorrosion methods. One is to control the temperature, and the other is to add preservatives. Below 20°C, 

bacteria reproduce slowly, and above 25°C, bacteria reproduce quickly. However, because the oil emulsion may precipitate sediments below 

18°C, the oil temperature should be controlled at around 20°C. Preservatives are bactericides. The rear connection of the oil nozzle of 

high-speed spinning is prone to blockage, so bactericides must be included in the oil. Conventional spinning does not require it, but it must 

be cleaned frequently to keep the pipeline unobstructed. The amount of bactericide used is generally 110 to 500 ppm. After a period of use, 

bacteria will develop drug resistance, so its dosage should be increased. It is best to use two fungicides alternately to improve drug resistance.

Ⅲ.POY and DTY oils

1. POY oils The spinning speed of high-speed spinning is above 3000m/min, and the amount of oil applied is lower than that of conventional 

spinning. Therefore, the oil is required to have good interface properties, easy dispersion and penetration, and can be evenly attached to the 

fiber surface. The oil is one of the key factors in winding and forming. It should make the obtained winding bobbin well formed and the 

unwinding tension small.

POY is mainly used for stretching deformation. The yarns must be processed under high temperature, high tension and high contact pressure. 

Therefore, the POY oil must have heat resistance, high oil film strength and less white powder.

1.1 Components and properties of POY oils

Like other oils, the main component of POY oils is smoothing agent (accounting for 60% to 95%). There are four major categories of substances 

that can be used as lubricants, including mineral oil, fatty acid esters, polyol esters, and polyethers. Their properties determine the properties of 

the oil (see the table below)

Performance comparison of four lubricant components

Table

The main component of lubricants in high-speed spinning oils is polyether

Polyether can reduce the static friction coefficient between fibers, which is beneficial to elasticization, but it increases the dynamic friction 

coefficient between fibers and metals, which is not conducive to stretching. Polyether has good heat resistance and is difficult to volatilize. The 

oil that the silk thread is thrown onto the surface of the heat pipe or hot plate during high-speed rotation during stretching deformation can be

 decomposed into carbon dioxide and water, leaving less tar residue. In addition, the polyethers of different molecular weight ranges are mixed 

in a certain proportion, and sometimes a small amount of other ingredients are added to make up for the deficiencies of the polyethers listed in

 Table 12-3.

Since the antistatic agent is an anionic compound of alkyl phosphate ester salts and alkyl sulfate ester salts, which has poor heat resistance, the 

content in the oil should be reduced to about 1% to 2%. Anionic compounds have wettability, wear resistance, and adhesion, which can improve

 the interface characteristics of the oil.

Emulsifiers are non-ionic surfactants, and commonly used organic compounds include alkylphenol ethers and fatty acid esters. In addition to 

emulsifying oils, they can also increase the compatibility of lubricant polyethers and anionic antistatic agents, enhance the strength of oil films 

and the bundling of filaments.

Fatty acids, fatty alcohols, alcohol ethers and other regulators should also be added to high-speed spinning oils to enhance the thermal stability,

 antioxidant properties and emulsion stability of the oils.

1.2 Use of POY oils

POY oils make the dynamic friction coefficient between fibers and metals larger, so POY is generally not suitable as the raw yarn for drawing 

multifilaments. When the friction coefficient is too large, hair and broken ends will appear during drawing, affecting product quality.

POY oils are mostly applied to fibers by oiling the nozzle. In order to prevent the nozzle from clogging, the oil should be filtered and bactericide 

added. Because the delivery pressure of the oil pump fluctuates, this fluctuation has little effect when the oiling amount is high; when the oiling 

amount is 0.2% to 0.3%, it is difficult to apply evenly. When the oiling amount is 0.3%, it is easy to produce hairy silk.

2. DTY oil

DTY oil is a finished oil, of which 90% to 92% is composed of white oil, and the rest is emulsifier, antistatic agent and regulator. Compared with 

conventional spinning stretch yarn oil, DTY oil is mainly uniform in oiling at high speed, with high oil film strength and good splash resistance, 

which can meet the needs of weaving and knitting.

The smoothness of DTY oil comes from the low viscosity mineral oil in the component. Mineral oil can not only meet the requirements of oil 

performance, but also reduce the friction coefficient between fiber and metal, increase the friction coefficient between fiber and fiber, make the 

fiber have good bundling, and the price is cheap.

The emulsifier uses non-ionic surfactant. The ester type has good emulsification, smoothness and good bundling of the fiber, and can improve 

the oil film strength. The ether type has good emulsification, compatibility, smoothness and antistatic properties

The regulator contains silicone oil, thickener and other substances. Silicone oil can reduce the surface tension of the oil and improve the 

softness of the yarn. The thickener is a cationic surfactant, which can not only keep the oil in proper viscosity when applying oil, but also 

increase the viscosity of the oil and prevent the oil from splashing. The regulator also has anti-corrosion properties.

IV. Varieties of polyester filaments

1., virgin yarn:

Undrawn yarn (conventional spinning) (UDY), semi-pre-oriented yarn (medium-speed spinning) (MOY), pre-oriented yarn (high-speed spinning)

 (POY), high-oriented yarn (ultra-high-speed spinning) (HOY)

2. Drawn yarn:

Drawn yarn (slow-speed drawn yarn) (DY), fully drawn yarn (spinning and drawing one-step method) (FDY), fully drawn yarn (spinning one-step 

method) (FOY)

FDY refers to filament, also called fully drawn yarn. POY is called pre-oriented yarn, which refers to the orientation degree obtained by 

high-speed spinning between unoriented yarn and drawn yarn

3. Deformed yarn:

Conventional deformed yarn (DY), drawn deformed yarn (DTY), air-deformed yarn (ATY).

DTY refers to polyester low-elastic yarn, also called stretched textured yarn.