To impart a soft, smooth, or full hand feel to fabrics, most textiles undergo finishing with softening agents in addition to mechanical finishing.

 

I. The Function of Softeners

 

1. Replenish the natural oils lost during scouring, bleaching, and other processing steps to achieve a more desirable hand feel.

 

2. Adheres to natural or synthetic fibers, enhancing smoothness and strength while improving hand feel.

 

3. Enhance the wear performance of fabrics by leveraging certain properties of softening agents.

 

To achieve the aforementioned effects, softening agents are typically oil-based substances that impart smoothness and a pleasant hand feel. When applied to the fiber surface, they reduce inter-fiber friction, thereby providing lubrication and softness. Additionally, some softening agents can form crosslinks with reactive functional groups on the fibers, enhancing wash durability.

 

II. Requirements for Softeners

 

1. The working fluid must remain highly stable under all soft-processing conditions.

 

2. Does not reduce the whiteness or colorfastness of fibers or fabrics.

 

3. Fibers or fabrics that have undergone softening treatment are resistant to heat-induced discoloration and should not exhibit changes in color, hand feel, or odor during storage.

 

4. If the fabric softener is an emulsion, it must exhibit good emulsion stability.

 

5. Depending on the specific processing requirements, the fabric should exhibit appropriate water-absorbing or water-repellent properties, antistatic characteristics, and other desired performance attributes (selection should be made based on the particular requirements of the fabric). It should also possess wash resistance or dry-cleaning resistance.

 

6. No adverse effects upon skin contact.

 

Given the wide variety of textile types, the diverse fibers used, the differing fabric specifications, and the varied end-use applications, the requirements for finishing treatments also differ. Therefore, the selection of a softening agent cannot be made in a one-size-fits-all manner; rather, it should be based on the softening mechanisms and functional characteristics of each type of softener to choose the one that best meets the specific requirements. In addition, no single softener can deliver an unlimited range of performance attributes; to achieve well-balanced results across multiple properties, two or more softeners can be used in combination (or blended into a new, composite softening formulation). For example, combining silicone-based softeners with long-chain aliphatic softeners can yield excellent hand feel—soft, full-bodied, and smooth—and when such softening treatments are integrated with mechanical softening processes, even better results are often obtained.

 

III. Types of Softeners

 

Softening agents constitute the largest and most diverse category of dyeing and finishing auxiliaries. According to reports, among the 920 domestic and international auxiliary samples collected by the Shanghai Institute of Printing and Dyeing Technology between 1990 and 1999, 350 were softening agents, accounting for 38%. Given such a wide variety of softening agents, their chemical structures generally indicate that they are Two major categories: long-chain aliphatic compounds and polymeric polymers. In the molecular structure of long-chain aliphatic softening agents, the long hydrocarbon chains can adopt a randomly coiled conformation, imparting molecular flexibility. These flexible molecules adsorb onto the fiber surface, acting as a lubricant and reducing both the dynamic and static coefficients of friction between fibers.

 

Therefore, long-chain aliphatic structures generally exhibit excellent softening effects; in softening agents, they are not only available in a wide variety of types but are also used in relatively large quantities. This type Softening agents can be classified according to their ionic nature into anionic, cationic, nonionic, and amphoteric types. In addition, natural oils and paraffin-based softeners, being inherently lubricating substances, may also be classified as a separate category; however, depending on the ionic nature of the emulsifiers used, they can alternatively be assigned to different ionic classes. Softening agents based on polymeric polymers mainly fall into two major categories: polyethylene and organosilicon compounds. Polyethylene-based softeners are relatively limited in variety and used in smaller quantities, with silicone softeners being the most widely employed. This is because the polysiloxane backbone adopts a highly flexible, helical, linear structure that can rotate freely through 360 degrees with virtually no energy input. Consequently, the molecular architecture of polysiloxanes aligns perfectly with the mechanisms underlying fabric softening: they not only reduce both static and kinetic coefficients of friction between fibers but also exert very weak intermolecular forces, thereby lowering fiber surface tension—making them an ideal material for textile softening finishes. Silicone softeners have emerged as the fastest-growing category of softening agents in recent years.

 

IV. Anionic Softeners

 

Anionic softeners, in addition to soaps and sulfonated oils, primarily consist of sodium octadecyl succinate sulfonate, octadecyl sulfate ester, and other cationic, anionic, or nonionic compounds containing long-chain alkanes. It generally exhibits excellent wettability and thermal stability, can be used in the same bath as fluorescent whitening agents, and serves as a softening agent for extra-white fabrics. It is also well suited for cellulose fibers. Can impart good water absorbency to fabrics. However, its adsorption onto fibers is similar to that of direct dyes—relatively weak—resulting in poor softening effects and easy wash-out. In addition, because it has Soft in the bath It functions to refine silk, thereby preventing abrasion (graying).

 

V. Nonionic Softeners

 

Nonionic softeners are generally polyoxyethylene esters (or ethers) of decanoic acid (or alcohols), or fatty esters of pentaerythritol or sorbitol. Due to Nonionic softeners exhibit weaker adsorption onto fibers than ionic softeners. , it can only provide a smoothing effect. However, it can be used in combination with ionic softeners and other Good compatibility , to Good electrolyte stability , and It does not have the drawback of yellowing the fabric. It can serve as a non-durable softening finish or as an important component of spinning oils for synthetic fibers. Certain products can also be used as silk-like finishes to impart a “silk-sound” effect to fabrics.

 

VI. Cationic Softening Agents

 

There are many varieties of this type of softener, and it is currently the most widely used.

 

This is mainly because most fibers carry a negative charge in water, allowing cationic softeners to adsorb readily onto the fiber surface with strong binding affinity, enabling It exhibits excellent high-temperature resistance and wash durability, and the finished fabric is full-bodied and smooth, with improved abrasion resistance and tear strength; moreover, it imparts a certain antistatic effect to synthetic fibers. Therefore, it is widely used for fabrics such as cotton, nylon, and acrylic; there are also varieties suitable for silk. However, some cationic softeners in High temperatures can easily cause yellowing, accompanied by a decrease in lightfastness.

 

Cationic softeners are generally derivatives of octadecylamine or dimethyl octadecylamine, or condensation products of stearic acid and polyethylenepolyamine. Based on their structure, they can be further classified into tertiary amine softeners, quaternary ammonium salt softeners, imidazoline quaternary ammonium salt softeners, and dialkyl dimethyl quaternary ammonium salt softeners, among others.

 

VII. Amphoteric Softeners

 

Amphoteric softeners are a class of softening agents developed to improve cationic softeners. Their It exhibits strong affinity for synthetic fibers and does not suffer from drawbacks such as yellowing or dye discoloration. It can also be used in the re-finishing process for silk to enhance its hand feel. Amphoteric softeners can further be combined with cationic softeners to achieve a synergistic effect. Such softeners typically have an alkyl amine lactone structure.

 

VIII. Organosilicon Softener

 

1. History of Silicone Softeners

• In 1863, French chemists C. Friedel and J. M. Crafts synthesized the first organosilicon compound containing a Si–C bond, SiEt4.
• In the late 1930s, Silicone resin It is made into.
• In 1940, Dimethyl silicone oil Was manufactured.
• In 1943, Dow Chemical and Corning Incorporated formed a joint venture to establish Dow. Corning (Dow Corning, DC) is a company specializing in the production and research of silicones. In 2016, Dow Chemical acquired Corning’s stake, bringing Dow Corning’s 73-year history to an end.
• In 1947, General Electric (GE) established its silicones division. In 2006, Apollo Global Management acquired GE’s silicones business for US$3.8 billion, officially establishing Momentive Performance Materials Inc. (MPM). In 2010, Apollo merged Momentive with Hexion Inc., thereby establishing Momentive Performance Materials Holdings Co., Ltd. In May 2019, a consortium comprising South Korea’s KCC, Wonik QnC, and SJL Partners L.L.C. officially completed the acquisition of Momentive Performance Materials!
• In 1947, a lecture titled “Silicon-Containing Plastics” delivered by Dr. Siegfried Nitzsche won over WACKER, prompting the company to immediately hire the young chemist. Dr. Nitzsche later came to be known as the “father of WACKER’s organosilicon business.” In 1949, Dr. Nitzsche and his colleagues successfully developed the first silane compound; shortly thereafter, the first silane production furnace was built and put into operation. By 1955, WACKER had produced its first silicon rods. In 2005, WACKER of Germany and its Chinese partner, Demei Fine Chemical Co., Ltd., established a joint venture to manufacture organosilicon products.
• In 1952, Bayer began producing silicones and later formed a joint venture with GE.
• In 1953, Shin-Etsu of Japan began producing silicones, and in 2002 it established Zhejiang Shin-Etsu Fine Chemical Co., Ltd.
• In 1954, Rhône-Poulenc of France established a new plant in Saint-Fons, founding a facility for the production of siloxanes and silicon derivatives. (This facility was later merged into Bluestar Silicones in China.)
• In 1966, Toray of Japan began producing silicones, which were later merged into Dow Corning.
• In 1968, Xinghuo Chemical Plant was officially established. In 1979, the State Petrochemical Ministry and the Jiangxi Provincial Planning Commission approved the construction of an organic silicon production facility at Xinghuo Plant with an annual capacity of 600 tons. In 1996, Xinghuo Organic Silicon joined China Bluestar Company 。
• In 1984, the founder of Bluestar Company led a team of seven individuals in securing a loan of RMB 10,000 to establish China’s first specialized cleaning firm. Since 2006, Bluestar has successively acquired Adisseo of France, Rhodia’s silicone and vulcanization businesses, and Chemours of Australia, thereby entering international markets and embarking on a global expansion strategy. In 2011, Bluestar acquired Elkem of Norway; in 2018, Elkem integrated Bluestar’s silicon value chain and was listed on the Oslo Stock Exchange, becoming the first Chinese-owned enterprise to be listed in Norway.
• China has become the largest consumer and producer of silicone materials.

 

2. Development of silicone softeners:

 

First generation: Dimethyl silicone oil, hydroxyl-modified silicone oil

Dimethyl silicone oil

Hydroxyl-Modified Silicone Oil

Characteristics: low cost, poor wash resistance, and easy emulsion breakdown; formerly used primarily as a spinning oil.

 

Second generation: epoxy-modified silicone softeners and amino-modified silicone softeners

 

Epoxy-Modified Organosilicon

Amino-Modified Organosilicon

Characteristics: hydrophobic and prone to emulsion breaking; epoxy-modified formulations emphasize dryness, while amino-modified formulations emphasize smoothness; amino-modified silicone oils, however, are susceptible to yellowing.

 

Third Generation: Polyether-Modified Organosilicone Softener

Polyether-modified organosilicon

 

Characteristics: good hydrophilicity and resistance to emulsion breaking, but slightly inferior hand feel.

 

Fourth Generation: Linear Block Copolymer-Modified Organosilicone Softener

Linear block copolymer-modified organosilicone oil

Features: excellent hydrophilicity, soft hand feel, low yellowing, and resistance to emulsion breakdown.

 

IX. Low-Molecular-Weight Polyethylene Emulsion

 

This type of softener is produced by oxidizing low-molecular-weight polyethylene followed by emulsification. It exhibits a certain affinity for fibers, imparting a smooth hand to fabrics. It can be applied in the same bath as resins and helps restore tear strength and abrasion resistance that are often reduced by resin finishing. Prior to the widespread adoption of silicone softeners, it served as an inexpensive auxiliary agent for achieving fabric softness and smoothness. Currently, this class of softeners is generally not used alone; rather, it is incorporated as a compounding ingredient in various softening formulations or employed as a stabilizer in hydroxyl-functional silicone emulsions.

 

(Source: Encyclopedia of Dyeing and Finishing)