Color difference of recycled plastic

        GB/T 40006 "Recycled Plastics" series of standards clearly define the technical requirements for various recycled plastic materials. The general requirements for the corresponding types of recycled plastics all mention "the particle size should be uniform and there should be no obvious color difference."

        Causes of color difference

        ◆The sources of raw materials are complex and diverse, and different batches or even different parts of the same batch may have obvious color differences.

        ◆The color difference caused by the thickness or diameter of the recycled plastic particles.

        ◆Caused by the technical process in the recycling process. For example, there is color difference caused by temperature adjustment differences due to water content, and there is color difference caused by the screen changing process and the time and frequency of screen changing.

        Color difference standards are missing

        Color difference is not only an aesthetic issue, but also a reflection of the quality and stability of recycled plastic particles. In terms of recycled plastic imports, color difference is also one of the important indicators for judging solid waste.

        However, there are no color difference standards in my country's recycled plastics field. There is no standard to rely on in the industry. The judgment of color difference is highly subjective and unstable, which may cause some problems. For example, the color difference judgment of different companies is inconsistent, resulting in uneven quality of terminal products, affecting the overall image and competitiveness of the recycled plastics industry. In view of this, it is particularly important to formulate relevant national standards.

        《Plastics - Determination of Color Difference of Recycled Plastics》

        In order to unify the measurement methods and improve market competitiveness, the national standard "Plastics - Determination of Color Difference of Recycled Plastics" (Plan No.: 20232459-T-606) came into being. This standard aims to use a spectrophotometer to measure the color difference of recycled plastics of various colors to characterize color uniformity and preliminarily evaluate the quality of recycled plastics.

        This standard specifies the method for determining the color difference of transparent or opaque recycled plastic particles. This standard is applicable to recycled plastic particles made from waste thermoplastics through screening, classification, cleaning, melt extrusion granulation (including granulation processes such as drawing, hot cutting and/or water cutting), etc. This part is also applicable to polyethylene terephthalate (PET) bottle flakes. The shape of the sample includes various shapes of waste plastics after granulation, such as flat, spherical, strip, irregular granular, etc. It is not applicable to plastics containing fluorescent agents. The color difference value and yellow index change value are used to evaluate the color uniformity of recycled plastics.

        If the plastic recycling industry wants to achieve high-quality development, produce high-quality recycled plastics, and expand the application scope of recycled plastics, especially the application of recycled plastics in food grade, it needs a series of national standards for recycled plastics as the underlying foundation to support the future development of the entire plastic recycling industry.