1. Who Collects Bottles After You Throw Them Away?
Bottles follow two main paths after you discard them. One path is municipal collection, where local governments gather bottles separated at home. The other is business collection, where companies collect bottles from vending machines, factories, offices, supermarkets, and stations [3]. In fiscal year 2024, municipalities collected about 310,000 tons, while businesses collected about 290,000 tons [4]. Bottles from vending machine boxes often enter the business path, which is nearly as large as the household path.
For home collections, consumers are responsible for separating containers under the Containers and Packaging Recycling Act. Municipalities roughly sort these into bundles called bales. Then, recycling companies turn them into flakes or pellets, and manufacturers make final products [5]. Homes are asked to remove caps and labels and rinse bottles quickly. However, some municipalities allow rings on caps to stay if they are hard to remove, so checking local rules is best [6].
When these bundles reach factories, they still contain caps, labels, and dirt. So, how are materials separated?
2. Why Does Water Separate Bottle Caps From Bottle Bodies?
Bottle bodies sink in water, but caps float. Factories use this difference to separate them. However, the exact process varies by company and equipment. According to a table in educational materials from Tottori Prefecture, PET plastic has a specific gravity of about 1.38, while polypropylene (common in caps) is 0.90. Water is 1.00, so there are processes that use this difference in density for sorting [7].
A business plan from Tochigi Prefecture shows one example of the steps: coarse crushing, wind sorting, fine crushing, gravity separation, washing, dewatering, and drying [8]. Wind blows away light items like labels, while water separates floating caps from sinking bottles. Note that this is just one company’s method; steps and machines differ elsewhere.
Also, cap materials vary, including polypropylene and polyethylene, so specific gravity differs depending on the material. After washing and drying, what do these bottle pieces become?
3. What Is the Difference Between Flakes and Pellets in Bottle Recycling?
Recycling companies crush bottles into small pieces about 8mm square, then wash and dry them. These pieces are called flakes. The word "flake" means thin slice in English, but here it refers to crushed bottle bits [9]. If flakes are melted and formed into tiny granules, they become pellets. Pellets are easier to transport and store, often used for making fibers.
Flakes and pellets become different products. Fibers become uniforms, car interiors, or carpets. Sheets become food trays or egg cartons. Molded items become cable ties or construction materials [3]. Recycled flakes are also exported; in fiscal year 2024, about 120,000 tons went to Southeast Asia, Taiwan, and the US as flakes.
In the past, clothes and trays were the main destinations for recycled plastic. What is happening now?
4. Why Do About 60% of Recycled PET Resins Become New Bottles?
In fiscal year 2024, total domestic recycled PET resin was about 426,000 tons. Of this, "bottle-to-bottle" recycling accounted for about 246,000 tons, or 57.7% [2]. Sheets were 25.5%, and fibers were 7.8%. Note that 57.7% is the share within recycled resin. If compared to total sales of 652,300 tons, it is about 37.7% (author’s calculation). Do not mix these two percentages as they have different denominators.
Bottle-to-bottle means turning food bottles back into food bottles. There are two methods: chemical recycling breaks resin down to the molecular level and rebuilds it. Mechanical recycling washes flakes thoroughly, treats them at high heat to remove dirt from the resin, and makes pellets [10]. Both start by making flakes.
Standard material recycling cannot fully remove dirt. To use recycled plastic for food containers, safety checks were needed. The Food Safety Commission allowed the use of chemical recycling for direct food contact in 2004. Mechanical recycling got its first domestic system in 2011, and the Ministry of Health, Labour and Welfare issued guidelines for food container plastics in April 2012 [11]. Note that different government bodies approved these methods.
The Association explains that by thoroughly removing foreign objects, quality equal to original bottles can be restored, enabling repeated recycling. However, no number is given for how many times this can be done.
5. What Is the Difference Between the 91.9% Collection Rate and the 85.1% Recycling Rate?
Two similar numbers appear in bottle statistics. For fiscal year 2024, the collection rate was 91.9% (collected weight divided by sales weight), and the recycling rate was 85.1% (recycled weight divided by sales weight) [1][4]. The 6.8-point difference is mainly due to how items are counted. Collection rates include caps, labels, and foreign objects in the weight. Recycling rates count only the bottle body, excluding those parts [4]. However, we cannot say all of the difference is just caps.
In international comparisons, Japan’s recycling rate was 85.1% (fiscal year 2024), Europe was 42.7%, and the US was 19.6%. Europe and the US figures are from 2021, so years do not match [12]. Calculation methods may differ by region, so these numbers should not be used to judge superiority.
6. How Can You Test Where Bottle Caps Go With Water at Home?
You can test separation at home. Put water in a cup and gently place a bottle cap on the surface. See if it floats or sinks. Since caps are made of different materials, results may vary. Try comparing other small plastic items from your house.
Look at labels on bottles for identification marks or signs showing recycled PET use. You can also check your local municipality’s sorting rules to see how they handle caps and labels.
If you want to read more, the PET Bottle Recycling Promotion Association page is in Japanese and shows the flow from collection to products, along with yearly figures [3].