Polyurethane (PU) can transform into a strong adhesive, firmly bonding tiles to walls; it can also become plastic parts like phone cases and keyboard keycaps; and even become shoe soles and sealing strips, exhibiting elasticity comparable to rubber. Why can the same material freely switch between the seemingly unrelated fields of "adhesive, plastic, and rubber"? Today, we'll uncover the secret of this "versatile" material by delving into the underlying logic of its molecular structure. What are the essential differences between adhesive, plastic, and rubber? Don't rush to say "you can tell from the application." From a materials science perspective, their core differences lie in their molecular chains: Material  type Core Features Essence Key features at the molecular level Glue Materials that can actively wet interfaces, bond with interfaces through chemical/physical interactions, and ultimately solidify to form stable bonds. Materials containing polar groups (such as -NH-, -COO-), easily forming hydrogen bonds or chemical bonds; capable of forming network structures through cross-linking reactions. Plastic Materials with a certain degree of rigidity, capable of maintaining their shape and not easily deformed under stress. Molecular chains arranged regularly (crystalline) or forming cross-linked networks, with restricted chain segment movement and small free volume. Rubber Materials with high elasticity, capable of large deformations and rapid rebound, and not easily permanently damaged after deformation. Molecular chains soft (low Tg), with free chain segment movement; possessing moderate cross-linking or physical anchoring points to restrict excessive chain segment movement. And polyurethane happens to have the "code" for all three properties written into its molecular structure. The Molecular Structure of Polyurethane The molecular chain of polyurethane consists of two key structural parts: Soft segments: usually derived from long-chain polyols (such as polyethers and polyesters), like soft ropes, can swing freely, giving the material flexibility and elasticity. Hard segments: Formed by the reaction of isocyanates and chain extenders, these segments have short, rigid molecular chains and can cluster together via hydrogen bonds to form crystalline regions, resembling small pebbles that provide strength and stability. These two types of segments are covalently linked, yet they behave like oil and water, "not interfering" with each other—soft segments aggregate together, while hard segments clump together, forming a "microphase separation" structure. It is this structure that allows polyurethane to achieve "free adjustment" of its properties: add more hard segments for a harder texture, and increase the proportion of soft segments for a softer texture. Why can it be used as an adhesive? Many types of tile adhesive used in home renovations and structural adhesives used in carpentry are made of polyurethane. Its strong adhesion relies on two ...

Film-Forming Aids Polymers that make up emulsions or dispersions typically have glass transition temperatures above room temperature. To ensure good integration of emulsion particles into a uniform paint film, film-forming aids must be used to lower the minimum film-forming temperature (MFFT). Film-forming aids are a class of small-molecule organic compounds that eventually escape and volatilize from the paint film. Most film-forming aids are a significant component of volatile organic compounds (VOCs) in coatings; therefore, the less film-forming aid used, the better. When selecting film-forming aids, prioritize compounds that are not subject to VOC restrictions but have moderate volatility and high film-forming efficiency. The amount of film-forming aid depends on the amount of emulsion or aqueous dispersion in the formulation and the glass transition temperature. For emulsions or aqueous dispersions with high Tg values, a larger amount of film-forming aid is required, and vice versa. When designing a formulation, the film-forming aid should ideally comprise approximately 3%-5% of the emulsion or aqueous dispersion, or 5%-15% of the solids content. However, for polymer emulsions with Tg values exceeding 35°C, the amount of film-forming aid may need to be increased to ensure reliable low-temperature film formation. In this case, the amount of film-forming aid should be gradually increased until a uniform, non-cracking, non-powdering paint film can be formed at low temperatures (around 10°C or lower), thus determining the minimum required amount. Using film-forming aid at 15% or higher of the emulsion or dispersion is not advisable; alternative film-forming aids should be considered. Besides lowering the minimum film-forming temperature and increasing film density, film-forming aids can also improve workability, increase leveling properties, extend open time, and improve storage stability, especially low-temperature antifreeze properties. Film-forming aids in water-based coatings are generally alcohol ether solvents, most commonly diethanol ethers, propylene glycol ethers, and N-methylpyrrolidone, which vary in boiling point. During summer application, water-based coatings dry relatively quickly, meaning some moisture may remain trapped within the coating film before it is fully dry, leading to whitening or poor leveling. Therefore, adding a small amount of appropriate high-boiling-point solvent can slow down the drying process, extend the open time of the film, and improve its application properties and appearance. In winter, due to lower temperatures, water-based coatings dry more slowly, meaning water evaporates more slowly. However, film-forming aids evaporate relatively faster than water, and some may not evaporate with the water. This can prevent the water-based coating from forming a dense layer, resulting in whitening and cracking of the film. Therefore, when adding film-forming aids, it is essential to consider overcoming the application...

In water based paint formulations, the base material is the key component that forms the paint film and determines its performance. When designing the formulation, the amount of waterborne resin should be maximized, accounting for 60-70% by volume, to ensure the highest possible content of effective film-forming agents in the paint. This guarantees a thicker, fuller paint film in a single coat. Waterborne Acrylic Resins Acrylic emulsions, due to their versatility, weather resistance, and diversity, have been widely used in various fields of the coatings industry. Waterborne acrylic emulsions are produced by emulsion polymerization of vinyl monomers, primarily acrylate monomers. Various additives, such as emulsifiers, stabilizers, and pH adjusters, are added during the polymerization process, making the system quite complex. Paint films made from waterborne acrylic emulsions have good weather resistance, are less prone to yellowing, have high hardness, and good gloss. In recent years, with the continuous development of waterborne acrylic emulsion polymerization technology, multiphase polymerization, core-shell technology, self-crosslinking technology, and the application of polymeric surfactants, the properties of waterborne acrylic emulsions have been further improved and enhanced. This has expanded the application range of waterborne acrylic emulsions to meet the needs of different construction and usage conditions. Currently, the application of waterborne acrylic emulsions has expanded to industrial applications with higher performance requirements. Polyurethane Dispersions Polyurethane materials are a general term for a class of macromolecular compounds with urethane structures in their molecular structure, usually produced by polyaddition reactions of diisocyanates and polyols. Polyurethane polymers possess both polar functional groups that enable physical crosslinking and non-polar and flexible segments. When used properly, their polar functional groups can undergo further chemical crosslinking. These molecular characteristics give polyurethane materials high strength, toughness, and solvent resistance. As a high-strength, weather-resistant, and strong-adhesion material, polyurethane has been widely used in the coatings industry. Based on the type of isocyanate used in the preparation of polyurethane, polyurethane emulsions and corresponding paints can be divided into two main categories: aliphatic and aromatic. Aliphatic paint films exhibit excellent weather resistance and anti-yellowing properties; aromatic waterborne polyurethanes are mostly used for interior decorative paints. According to the particle size obtained from polymerization, polyurethane emulsions and polyurethane dispersions are also classified. Waterborne polyurethane dispersions utilize a unique process to disperse polyurethane particles in water, thereby achieving film formation with water as the carrier. Similar to the film-forming mechanism of other emulsions, the film-...

Waterborne coatings, including waterborne wood coatings, are coatings that use water as the dispersion medium and diluent. Unlike less commonly used solvent-based coatings, their formulation systems are much more complex. Formulation design requires attention not only to the type of polymer, the properties of the emulsion and dispersion, but also to the rational selection of various additives and the consideration of the interactions between components for proper matching. Sometimes, special additives are needed for specific requirements, ultimately forming a suitable formulation. Basic Components of the Formulation: 1) Waterborne Resin: This is the base material for film formation, determining the main function of the paint film. 2) Film-forming aids: After water evaporation, these help the emulsion or dispersion particles form a uniform and dense film, and improve film-forming properties under low-temperature conditions. 3) Defoamers and antifoams: These suppress bubbles generated in the paint solution during production and allow existing bubbles to escape to the surface and break down. 4) Leveling agents: These improve the paint's application properties, forming a smooth and glossy coating. 5) Wetting agents: Improve the wetting properties of the paint on the substrate, enhance leveling, and increase the adhesion of the paint film to the substrate. 6) Dispersants: Promote the dispersion of pigments and fillers in the paint. 7) Rheology modifiers: Provide good flowability and leveling properties to the paint, reducing defects during the coating process. 8) Thickeners: Increase the viscosity of the paint, improve the wet film thickness of a single coat, and prevent sedimentation and delamination in putty and solid color paints. 9) Preservatives: Prevent the paint from mold growth during storage. 10) Fragrances: Give the paint a pleasant odor. 11) Colorants: Primarily for colored paints, enabling water-based paints to achieve the desired color. Colorants include two main categories: pigments and dyes. Pigments are used for solid color paints (coatings that do not show wood grain), while dyes are used for transparent paints (coatings that show wood grain). 12) Fillers: Primarily used in putties and solid color paints to increase solids content and reduce costs. 13) pH Adjusters: Adjust the pH value of the paint solution to stabilize it. 14) Wax Emulsions or Powders: Improve the scratch resistance and feel of the paint film. 15) Special Additives: Additives added to meet the specific requirements of water-based paints, such as rust inhibitors (to prevent premature rusting in tin cans), hardeners (to increase the hardness of the paint film), matting agents (to reduce the gloss of the paint film), scratch inhibitors, slip agents (to improve the feel of the paint film), anti-blocking agents (to prevent coatings from overlapping and sticking), crosslinking agents (to create two-component paints and improve overall performance), water repellents (to giv...