With the development of the chemical industry, people's living standards have been continuously improving. However, along with significant improvements in living conditions, serious environmental issues have arisen, even affecting human health and safety. As people's demand for health has gradually increased, the safety of ubiquitous chemical products in daily life has attracted widespread attention. Dishwashing detergent, as a chemical product widely used in both daily life and industry, has attracted particularly high attention regarding its safety.
The safety of chemical products once fell into a crisis of trust, stemming partly from the heavy reliance of detergent production on traditional raw materials, and partly from the lack of relevant professional knowledge among the public regarding chemical production.
Against this backdrop, we have designed and developed detergent formulations based on the core principle of green chemistry - "to reduce and eliminate pollution to the environment at the source." In this detergent, we have utilized environmentally friendly surfactants and related chemical agents that inhibit microorganisms in water.
Since entering civilized society, washing activities have been an indispensable part of human life. About 5000 years ago, humans began washing activities using alkaline substances such as those extracted from plant soapberries and wood ash, which are naturally conducive to washing. Three hundred years later, surfactants were manufactured. Over a hundred years ago, soap was created by humans, and since then, soap made from fats, alkalis, salts, fragrances, and colorants has become a traditional detergent. The first synthetic detergent, alkyl naphthalene sulfonate, appeared during World War I. It was developed by BASF in Germany in 1917 and officially put into production in 1925. The promotion of synthetic detergents began between 1935 and 1939 when alkyl benzene sulfonate and tetrapropylene benzene were discovered and put into production.
Today, synthetic detergents have become the dominant products in the detergent industry, surpassing traditional soap in both variety and quantity. Since the reform and opening up, China's economic structure has been continuously adjusted, with the light industry accounting for an increasing proportion of the national economy. The product structure of the daily chemical industry, closely related to human life, has been continuously improved with the increasing awareness of consumption among the Chinese people. The development potential of China's daily chemical industry in the 21st century is enormous.
In general, washing refers to the process of removing dirt from a surface. During washing, the interaction between dirt and the substrate is weakened or eliminated by the action of the detergent, causing the bonding between dirt and the substrate to transform into bonding between dirt and the detergent, ultimately leading to the detachment of dirt from the substrate through methods such as rinsing.
The basic process of washing can be represented by the following simple relationship:
Substrate·Dirt + Detergent
Substrate + Dirt·Detergent
Dirt adheres to the surface of an object through physical adhesion and chemical adhesion, with physical adhesion further divided into mechanical adhesion and electrostatic adhesion.
Chemical adhesion mainly refers to adhesion achieved through chemical bonds, such as the adhesion of proteins on fiber products and rust. Because chemical forces are generally stronger, the bonding between dirt and the substrate is more robust, making it very difficult to remove and requiring special methods for treatment.
Dirt adhering through physical adhesion has relatively weak bonding compared to chemical adhesion, making it relatively easy to remove. Mechanical adhesion of dirt is easy to remove, except when the dirt particles are very small (<0.1 um). Electrostatic adhesion occurs when charged dirt particles interact with opposite charges, making it relatively difficult to remove the dirt.
The washing process for removing dirt generally involves the following methods:
A. Adsorption, where surfactants in the detergent undergo directional adsorption at the interface between dirt and the substrate.
B. Wetting and penetration, where surfactants, due to their interface-oriented adsorption, can penetrate between dirt and the substrate, wetting the substrate and reducing the adhesion between dirt and the substrate.
C. Dispersion and stabilization of dirt, where dirt detached from the substrate surface is dispersed, emulsified, or solubilized in the detergent solution, ensuring that detached dirt does not reattach to the cleaned surface.
Dirt refers to oily substances adhering to a substrate and the adhesives of oily substances. Its composition is complex, but based on different forms, it can be roughly classified into solid dirt, liquid dirt, and special dirt.
The most common solid dirt includes rust, dust, carbon black particles, etc. These substances typically carry a negative charge on their surfaces, making them easily adsorb onto substrates. Generally, solid particle dirt is insoluble in water, but they are easily dispersed in aqueous solutions containing detergent. The larger the particle size of solid dirt, the easier it is to remove. Common liquid dirt is mostly oil-soluble and can undergo saponification with alkalis, which is why detergents are often alkaline. Special dirt includes substances that are difficult to remove, such as blood stains, plant juices, and bodily secretions. This type of dirt is mainly removed using bleach because the strong oxidative properties of bleach can destroy their chromophoric groups.
The primary active ingredient in detergents is surfactants, also known as surface-active agents. They dissolve rapidly in water and exhibit good cleaning, foaming, emulsifying, wetting, dispersing, etc.
Experiments have shown that adding certain substances to water can change its surface tension, and different substances have different effects on the surface tension of water.
In terms of reducing surface tension, we refer to the property that can reduce the surface tension of the solvent as surface activity, and substances with surface activity are called surfactants. We call substances that, when added in small amounts, cause a significant change in the interfacial state of the solution system, surfactants.
Surfactants are substances that, when added to a solvent, significantly reduce its surface tension, change the interfacial state of the system, and thus exhibit wetting or dewetting, emulsification or demulsification, dispersion or coagulation, foaming or defoaming, solubilization, moisturizing, sterilizing, softening, hydrophobic, antistatic, and anticorrosive properties to meet practical needs.
The earliest surfactants, soap-based surfactants, were discovered around 2500 BC in ancient Egypt, where a mixture of tallow and wood ash was used to make cleaning products. The first bar of soap was made around AD 70 by the Roman Empire's Pliny. It wasn't until 1971, when the French chemist Louis Boullay discovered the method of electrolyzing sodium chloride to produce caustic soda, that soap became popular.
The product of the second period of surfactant development is Turkey Red Oil, also known as sulfated castor oil, which is produced by reacting castor oil and concentrated sulfuric acid at relatively low temperatures, followed by neutralization with sodium hydroxide. Turkey Red Oil has excellent emulsifying, penetrating, wetting, and diffusing properties, and it performs better than soap in terms of resistance to hard water, acids, metal salts, etc.
The unique properties of surfactants stem from their special molecular structure. Surfactants generally have linear molecules containing both hydrophilic polar groups and hydrophobic nonpolar groups.
Hydrophobic groups can have various structures, such as straight chains, branched chains, and cyclic structures, with the most common being hydrocarbon chains, which can be alkanes, alkenes, cycloalkanes, aromatic hydrocarbons, with the number of carbon atoms mostly ranging from 8 to 20. Other hydrophobic groups include fatty alcohols, alkylphenols, groups containing fluorine or silicon, and other elements.
Hydrophilic groups can be categorized as anionic, cationic, zwitterionic, or nonionic. Anionic groups can electrolyze in water and carry a charge, while nonionic groups cannot electrolyze in water but have polarity and water solubility.
Surfactants are widely used in human life but are still chemical products. Many surfactants' raw materials have certain toxicity and pollution. Inevitably, they can harm the environment and cause irritation to the skin upon contact, with some even having strong toxicity and corrosiveness, causing significant damage to the human body. Below are introductions to several common harmful surfactants:
A. APEO: APEO is a common type of nonionic surfactant, composed of alkyl and ethoxy groups. Depending on the length of the former carbon chain and the number of added ethoxy groups, APEO can exist in various forms, each with significant differences in properties. While the main product of APEO synthesis is not carcinogenic, its by-products can corrode the skin and eyes, with severe cases leading to carcinogenesis. Although it does not directly harm organisms, APEO is associated with endocrine disruption. Chemicals enter the body in various ways and act like estrogen in the body, disrupting normal hormone secretion, resulting in reduced sperm production in males. Apart from human harm, its synthesis raw material, NPEO, is reported to be highly harmful to fish.
B. PFOS: PFOS, perfluorooctane sulfonate, is a type of perfluorinated surfactant known for its environmental persistence. Due to its unique physicochemical properties, PFOS is highly resistant to degradation, making it one of the most persistent substances. It accumulates significantly in organisms through the food chain, posing significant health risks.
C. LAS: LAS can cause significant harm to the environment. It is an important organic pollutant that alters the physicochemical properties of soil, such as pH and water content, making it difficult for plants to grow. Additionally, when LAS enters water bodies, it combines with other pollutants to form dispersed colloid particles, exhibiting toxicity to both higher and lower organisms.
D. Fluorocarbon Surfactants: PFOA and PFOS are the two main types of traditional fluorocarbon surfactants. However, research has shown that these compounds have high toxicity, causing persistent pollution to the environment and accumulating significantly in organisms. Therefore, they were listed as persistent organic pollutants (POPs) by the United Nations in 2009.
Amino acid surfactants are mainly derived from biomass, making them widely available. They have minimal toxic side effects, mild properties, low irritation to organisms, and good biodegradability. Amino acid surfactants can also be categorized into four types based on the charge properties of their hydrophilic groups after ionization in water: cationic, anionic, nonionic, and amphoteric. Common amino acid surfactants include N-alkyl amino acid types, amino acid ester types, and N-acyl amino acid types.
Pineapple enzyme surfactants are produced by fermenting tea seed cake, oil cake, pineapple peel, yeast powder, pectinase, and other fungal fermentation residues left after pressing oil from tea seeds. Although the molecular structure of its active ingredients is not yet clear, experimental data indicate that it exhibits good cleaning performance.
SAA is derived from palm oil, receiving widespread attention as a renewable plant-based material. Not only is its production process environmentally friendly, but it also precipitates calcium salts much slower in hard water with higher concentrations of calcium and magnesium ions compared to commonly used surfactants like LAS (Linear Alkylbenzene Sulfonate) and AS (Alkyl Sulfate). In practical applications, this slower precipitation implies superior cleaning efficiency.
Looking at the global market for detergent products, while different countries have different development focuses and trends, the general research direction for detergent products is similar. Concentration and liquidation have become mainstream trends, with water conservation, safety, energy efficiency, professionalism, environmental friendliness, and multifunctionality becoming hot directions for detergent product development. Moreover, the raw material for detergents—surfactants—is evolving towards mild, compound, and environmentally friendly types, with enzyme preparations possessing high efficiency, specificity, and environmental friendliness being a hotspot in detergent development. Overall, the development trends of the detergent industry mainly include:
Diversification and Specialization: Detergent products are becoming more diverse and specialized, with products divided into solid, powdered, liquid, and gel states. They are also categorized based on the concentration of active ingredients, with concentrated and regular types available. Additionally, they come in various packaging, colors, and scents.
Potential of Liquid Detergent Products: Liquid detergent products are poised to become the most promising type. Compared to solid detergent products, liquids offer better performance at low temperatures, more flexible formulations, simpler manufacturing processes, and require less equipment investment, thus saving energy.
Concentration: Detergent products are gradually becoming concentrated. Since 2009, three main categories of concentrated detergent products have emerged: concentrated laundry powder, concentrated laundry beads, and concentrated laundry liquid. Concentrated products offer significant advantages over traditional ones, including higher active ingredient content, stronger cleaning power, and energy savings.
Human Safety: As living standards rise, people's evaluation criteria for detergent products no longer focus solely on cleaning effectiveness but also on whether they are safe, non-toxic, gentle, and non-irritating to the human body.
Environmental Protection: Concerns over eutrophication caused by phosphate-containing detergents and negative environmental effects caused by bleaching agents have led to an increasing preference for environmentally friendly and mild detergent raw materials.
Multifunctionality: Multifunctionality is a trend in the development of various products in society. The phenomenon of "one product, multiple uses" is widespread in people's daily lives. Therefore, in the future, detergents will not only clean but also have functions such as sterilization, disinfection, and bleaching.
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