Raw Material Factors

• Purity of Raw Materials: Higher purity polyethylene raw materials generally lead to higher transparency of plastic bags. Impurities or other substances mixed in will reduce transparency. For example, adding recycled materials may darken the plastic bag, and adding fillers may whiten the bag, both of which affect transparency.
• Grade of Raw Materials: Even for the same polyethylene material, different grades of raw materials from different manufacturers can result in different properties and thus different transparencies of the produced plastic bags.
• Type of Opening Agent:
  • Chemical Purity: The chemical purity of the opening agent affects transparency. Chemically synthesized opening agents usually have higher purity than natural mineral opening agents, so the transparency of opening agents manufactured by chemical synthesis processes is significantly higher.
  • Addition Amount: The amount of opening agent added also matters. Different sources of crystal-type opening agents, such as natural mineral opening agents (heavy crystals) and chemically synthesized opening agents (light crystals), have different effects on transparency under the same volume due to their weight differences124.
  • Refractive Index: When direct light passes through the contact interface of two different materials, if the refractive indices of the two materials are the same, the direct light passing through has the least loss in the linear range of the original incident angle. However, if the refractive index difference between the two substances is large, the direct light passing through will lose more in the linear range of the original incident angle. Natural talcum powder and silica, for example, have a significant impact on the transparency of plastic bags due to their large attenuation of direct light.

Processing Technology Factors

• Film-forming Process: Different film-forming processes can influence the crystallinity and molecular arrangement of polyethylene films, thereby affecting transparency. For instance, the cast film process allows for rapid cooling, resulting in lower crystallinity and higher transparency, but with relatively lower barrier properties. In contrast, blown film has better tensile strength and opening properties, yet its transparency is slightly lower than that of cast film.
• Processing Temperature: If the processing temperature is too high or too low, it can have an adverse effect on transparency. Excessively high temperatures can cause defects such as bubbles and deformations on the film surface, hindering light transmission. On the other hand, if the temperature is too low, the plasticization effect will be poor, and the molecular arrangement will be uneven, also reducing transparency.
• Degree of Stretch: Appropriate stretching can orient the polyethylene molecules and improve transparency. However, excessive stretching may lead to uneven thinning of the film or even rupture, which instead decreases transparency.

Additive Factors

• Antioxidants: Antioxidants are often added to prevent polyethylene from being oxidized during processing and use. Some antioxidants may have a certain impact on transparency. Therefore, it is crucial to select the appropriate type and amount of antioxidants to minimize their effect on the transparency of plastic bags.
• Colorants: The addition of colorants to change the color of plastic bags will inevitably reduce their transparency. Even light-colored colorants will affect the light transmittance to some extent, decreasing transparency.

Film Thickness Factor