How Much Do You Know About Fabric Softeners?

As a textile industry expert, you're acutely aware that the final touch of fabric plays a pivotal role in customer satisfaction and product sales ??. Among all the value-adding processes, the adept use of fabric softeners stands out as a key element in enhancing product quality ??. This article will unveil how to effectively apply softeners to boost the smoothness and durability of fibers, ensuring your products stand out in a competitive market.

We will delve into how various softeners—be they traditional long-chain fatty acids or advanced silicone-based formulas—affect fiber properties like anti-static behavior, moisture absorption, and even colorfastness ??. More importantly, we'll guide you on selecting the right softener for different textiles, striking that perfect balance between comfort and wash resistance.

We understand that every decision in the production process is crucial, so the insights provided will be straightforward, enabling you to make swift and informed choices on the production floor ??. From cost-effectiveness to practical application, our precise guidance will help elevate your product quality, keeping you ahead in the competitive arena ??. Let's dive into the world of fabric softeners together and craft textiles that yield both high sales and rave reviews. ????

The Role of Fabric Softeners

① Supplement the natural oils lost during the refining and bleaching processes of natural fibers to improve the ideal hand feel.

② Improve smoothness and strength by adhering to natural or synthetic fibers, enhancing the overall hand feel.

③ Enhance the performance of fabrics in terms of wearability by utilizing certain characteristics of fabric softeners.

To achieve these effects, fabric softeners generally contain oily substances that provide smoothness and a desired hand feel. When they adhere to the surface of fibers, they reduce friction resistance between fibers, resulting in a lubricating and softening effect on the fibers. Some fabric softeners can also react with certain functional groups on the fibers to achieve wash durability.

Requirements for Fabric Softeners

① The working solution should be stable under various fabric softening conditions.

② Should not decrease the whiteness and color fastness of fibers or fabrics.

③ Fabric or fibers treated with fabric softeners should not undergo discoloration, changes in color, hand feel, or odor during storage or exposure to heat.

④ If the fabric softener is in the form of an emulsion, it should have good emulsion stability.

⑤ Depending on different processing requirements, it should possess appropriate water absorbency, water repellency, antistatic properties, etc. (selection should be based on specific fabric requirements). It should also be resistant to water washing or dry cleaning.

⑥ Should have no adverse effects on human skin upon contact.

Due to the diversity of textile types, variations in fiber usage, different fabric specifications, and varying requirements for finishing, fabric softeners cannot be generalized. Instead, fabric softeners should be selected based on their softening mechanism and functionality to meet specific requirements. Additionally, the performance of each fabric softener is limited, so combining the use of two or more fabric softeners (or formulating into a new fabric softener product) can often achieve better results, especially when combining silicone-based fabric softeners with long-chain fatty acid fabric softeners, which yield excellent softness, fullness, and smoothness. Combining the application of fabric softeners with mechanical softening can often yield very good results.

Types of Fabric Softeners

Fabric softeners are the most numerous and widely used type of auxiliary agent in the textile dyeing and finishing industry. According to reports, out of 920 domestic and foreign auxiliary samples collected by the Shanghai Institute of Printing and Dyeing Technology from 1990 to 1999, fabric softeners accounted for 350 samples, or 38%. These fabric softeners can be mainly categorized into two major chemical structures: long-chain fatty acid type and polymer type. The molecular structure of the long-chain fatty acid type allows for the formation of randomly arranged curled chains, which provide flexibility to the molecules. These flexible molecules adsorb onto the surface of fibers and act as lubricants, reducing the dynamic and static friction coefficients between fibers.

Therefore, the long-chain fatty acid type generally possesses good softening effects and has a wide variety of fabric softeners. Based on their ionic properties, these fabric softeners can be classified as anionic, cationic, nonionic, or amphoteric fabric softeners. Additionally, natural oils and paraffin-based fabric softeners, which are natural lubricating substances, can be classified as a separate category.

However, their classification can also depend on the ionic nature of the emulsifier used. Polymer-based fabric softeners mainly comprise polyethylene and organosilicon compounds. Polyethylene-based fabric softeners have a relatively limited variety and lower usage, whereas organosilicon fabric softeners are more commonly used. The main chain of polysiloxane is a highly flexible helical structure, allowing for 360-degree free rotation with minimal energy consumption. This molecular structure of polysiloxane aligns with the softening mechanism of textiles. It not only reduces the static and dynamic friction coefficients between fibers but also exhibits weak intermolecular forces, lowering the surface tension of fibers. As a result, polysiloxane is an ideal material for fabric-softening agents. Organosilicone fabric softeners have experienced rapid development in recent years and have become one of the fastest-growing categories of fabric softeners.

1. Anionic Fabric Softeners

In addition to soaps, sulfonated oils, etc., anionic fabric softeners mainly consist of long-chain alkyl ester sulfonate sodium salt, alkyl ester sulfate, and other long-chain alkyl compounds that are either cationic or nonionic. They generally possess good wettability and thermal stability, can be used in conjunction with fluorescent brighteners, and serve as fabric softeners for special white fabrics. They are also suitable for cellulose fibers and can provide good water absorbency to fabrics. However, their adsorption to fibers is similar to that of direct dyes, resulting in weaker softening effects and easy removal during washing. They can also be used for silk refining to prevent chafing (graying).

2. Nonionic Fabric Softeners

Nonionic fabric softeners are typically polyoxyethylene esters (or others) of decanoic acid (or alcohol), pentaerythritol, or sorbitol fatty acid esters. Since nonionic fabric softeners have weaker adsorption to fibers compared to ionic fabric softeners, they mainly provide a smoothing effect. However, they can be used in combination with ionic fabric softeners, exhibit good compatibility with other agents, have excellent electrolyte stability, and do not cause fabric yellowing. They can be used as non-durable fabric softeners or as important components in synthetic fiber spinning oil agents. Some products can also be used as artificial silk finishing agents to mimic the "creaking sound" of silk fabrics.

3. Cationic Fabric Softeners

Cationic fabric softeners are one of the most widely used fabric softener categories due to the majority of fibers having a negative charge in water. Cationic fabric softeners easily adsorb onto the surface of fibers due to their strong binding ability. They are resistant to high temperatures and washing, and fabrics treated with cationic fabric softeners feel full and smooth, improving the fabric's abrasion resistance and tear strength. They also exhibit certain antistatic effects, particularly on synthetic fibers. Therefore, they are widely used in cotton, nylon, acrylic, and other fabrics, as well as certain types of silk. However, some cationic fabric softeners tend to cause yellowing and a decrease in light fastness at high temperatures. Cationic fabric softeners generally consist of derivatives of octadecyl amine or dimethyl octadecyl amine or condensation products of stearic acid and polyethylene polyamine. Based on their structures, they can be further classified into tertiary amine fabric softeners, quaternary ammonium salt fabric softeners, imidazoline quaternary ammonium salt fabric softeners, and dialkyl dimethyl quaternary ammonium salt fabric softeners.

4. Amphoteric Fabric Softeners

Amphoteric fabric softeners are a type of fabric softener developed to improve cationic fabric softeners. They exhibit a strong affinity with synthetic fibers, do not cause yellowing or color changes in dyes, and can be used for silk finishing processes to improve the feel of silk fabrics. Amphoteric fabric softeners can also be used in conjunction with cationic fabric softeners to achieve a synergistic effect. These fabric softeners generally have alkylamine lactone-type structures.

5. Organosilicone Fabric Softeners

Organosilicone fabric softeners are emulsions or microemulsions of polysiloxane and its derivatives. They provide fabrics with excellent softness and a smooth hand feel. These products are produced through emulsion polymerization, emulsification of high molecular weight silicone oil, or modification and formulation processes. The range of products is quite extensive. However, the application effects and performance may vary.

① Dimethyl Silicone Emulsion:

These were the earliest silicone-based products used as fabric softeners. The relative molecular weight of the silicone oil used as a fabric softener is generally between 60,000 and 70,000. After finishing, it imparts a smooth, firm, and pleasant hand feel to fabrics, reduces the friction coefficient between fibers, and improves the fabric's abrasion resistance and sewability. However, since the molecular chains lack reactive groups, they cannot react with fibers or self-crosslink. Instead, they rely on molecular adsorption onto the fiber surface, resulting in poor wash durability and limited improvement in elasticity.

② Hydrophilic Soluble Silicone (Hydroxyl Silicone Emulsion):

This type of silicone fabric softener was widely used in the 1980s. The relative molecular weight is generally between 60,000 and 80,000, with higher molecular weights providing better softness and smoothness. Due to the presence of hydroxyl groups at the end and side chains of the silicone macromolecule, when combined with crosslinking agents and catalysts, it can react with reactive groups on the fiber surface or self-crosslink to form a polymer film with certain elasticity. Therefore, it has good wash durability and can improve the fabric's elasticity. Hydrophilic soluble silicone emulsions can be further classified into cationic hydrophilic silicone emulsions and anionic hydrophilic silicone emulsions based on the ionic nature of the emulsifier. Although hydroxyl silicone emulsions improve the hydrophilicity and emulsion stability of the silicone, controlling the particle size of the emulsion is challenging. This can result in poor emulsion stability, leading to oil floatation issues during application and difficult-to-remove oil stains on fabrics. Therefore, the emulsion stability of hydrophilic silicone emulsions is an important indicator of their quality.

③ Amino-Modified Organosilicone:

By introducing amino groups onto polysiloxane, the performance of organosilicon can be significantly improved. The amino groups not only form strong orientational and adsorption interactions with fibers, reducing the friction coefficient between fibers but also react with epoxy groups, carboxyl groups, and hydroxyl groups. This makes it suitable for various fibers, including cotton, wool, silk, viscose fibers, polyester, nylon, acrylic, and their blends. Fabrics treated with amino-modified organosilicon exhibit excellent softness and resilience, with a soft and full hand feel. Generally, the higher the amino content, the better the softness. However, higher amino content also means more prone to yellowing due to the synergistic effect of oxidation. This is mainly because the side chain of the polysiloxane contains two amine groups (primary and secondary amines), which have three active hydrogen atoms and are prone to oxidation, leading to color formation. Therefore, there needs to be a balance between amino content and yellowing. An amino-modified organosilicon can be formulated into a microemulsion, which has rapidly developed in the past decade. Due to the introduction of amino groups, the hydrophilicity of the organosilicon is improved. Thus, with the appropriate emulsifier and preparation process, a microemulsion with a particle size below 0.15 μm can be achieved. Since the particle size is smaller than the wavelength of visible light, the microemulsion appears transparent. The smaller particle size in microemulsions results in an increase in the effective number of particles by 103 times (at the same concentration). The microemulsion has a greater contact opportunity with the fabric, exhibits good spreading properties on the fabric's surface, and easily penetrates the fiber's interior. Therefore, this type of product imparts excellent internal softness to fabrics, which is more durable. Microemulsions also offer better water solubility, storage stability, heat stability, and shear stability.

Amino-modified organosilicon is known to exhibit excellent softening effects. However, their whiteness, water absorbency, and ease of cleaning are relatively poor and tend to worsen with an increase in amino groups in the polymer.

To improve these drawbacks, modifications can be made by changing the type and quantity of amino groups. Modifying the type of amino group involves converting primary amines into secondary or tertiary amines. For example, silicone-based fabric softeners modified with N-propylmorpholine (secondary amine) and N-propylpiperazine (tertiary amine) have been developed and used for fabric softening. These fabric softeners reduce yellowing during baking and exhibit less hydrophobicity compared to silicone fabric softeners with primary amine groups. However, they may impart a slightly dull hand feel to fabrics. They are primarily used for softening bleached and light-colored fabrics. In addition, to achieve a super-smooth hand feel, the ends of the macromolecular chains of dimethylsiloxane can be modified with amino groups, resulting in a very orderly and aligned arrangement on the fabric's surface, thus providing an excellent smooth hand feel. If some side chain groups and end groups of polysiloxane are replaced by amino groups and used as fabric softeners, they can provide better fabric softness. Organosilicone fabric softeners have developed rapidly, with an increasing number of varieties and lower prices. The use of organosilicon fabric softeners has significantly increased. In addition to the aforementioned types of organosilicon fabric softeners, there are also epoxy-modified, amide-modified, and carboxyl-modified organosilicon fabric softeners.

6. Low Molecular Weight Polyethylene Emulsion

This category of fabric softeners is produced by oxidizing low molecular-weight polyethylene and then emulsifying it. They exhibit a certain affinity with fibers, providing fabrics with a smooth hand feel. They can be used in conjunction with resins and improve tear strength and wear resistance, which may decrease due to resin finishing. They are cost-effective fabric softening and smoothing agents before the widespread use of silicone fabric softeners. Currently, they are generally not used independently but as components in various fabric softener formulations or as stabilizers in hydroxyl silicone emulsions.