The recycling and reuse of woven bags refers to PP plastic waste suitable for manufacturing such bags. This is a form of waste valorization that demands stringent standards: the material must not be mixed with other plastics and must be free of sediments, impurities, and mechanical contaminants. Its melt index should fall within the range of 2–5 (and it cannot consist entirely of polypropylene). Such material primarily originates from two sources: scrap generated during the production of woven bags, and recycled products made from used PP bags, including woven sacks, fertilizer bags, and cement bags.

Recycling method for PP woven bags using a plastic pelletizing machine:

There are two main methods: the melt granulation method and the extrusion granulation method, with the latter being the more widely used. The two methods are as follows:

Waste from the molten granulation process → Material selection and washing → Drying → Cutting → High-speed agglomeration (feeding → thermal shrinkage → spraying → agglomeration) → Discharge packaging;

Waste from the extrusion granulation process → water washing → air drying → strip cutting → heated extrusion (using a plastic extrusion granulator) → cooled pellet cutting → packaging.

The equipment used in the extrusion process is a self‑made plastic extrusion granulator. To remove gases generated during waste‑gas extrusion, an exhaust‑type extruder may also be employed. To eliminate impurities in the waste stream, an 80–120 mesh screen is installed at the extruder’s discharge end.

The utilization of recycled materials and their impact on the performance of polypropylene (PP) bags. Due to thermal aging during plastic processing, the properties of recycled woven bags are significantly degraded—particularly after two or more cycles of thermal processing—compounded by prior UV‑induced aging.

Adjusting the wire-drawing process using recycled materials

The melt index of recycled PP increases with prolonged processing time, owing to thermal aging caused by repeated thermal cycling and UV‑induced degradation during long-term service. Consequently, when incorporating substantial amounts of recycled material into a new formulation, it is advisable to appropriately adjust the extrusion temperature, die temperature, and draw‑down setting temperature, and to measure the melt index of the blend to determine the extent of necessary adjustments.

On the other hand, because recycled materials undergo multiple processing steps, their molecular weight decreases, resulting in a high proportion of short-chain molecules, and they are subjected to repeated stretching and orientation. Consequently, during production, the draw ratio is lower than that of the corresponding virgin material. Typically, the draw ratio for virgin resins is 4–5, whereas for recycled materials it is generally 3–4. At constant screw speed and temperature, as the melt index of the recycled material increases, its viscosity decreases, the extrusion rate rises, and the draw speed also increases slightly. When blending new and recycled resins, care should be taken to ensure uniform mixing, and it is advisable to select materials with similar melt indices for compounding. A large difference in melt index or a significant disparity in melting points can prevent both resins from being plasticized simultaneously during extrusion, severely hindering the extrusion‑drawing process, increasing the scrap rate, and even making production impossible.

Our factory’s PP/PE recycled‑plastic pelletizing machines are primarily used to process waste plastic films, woven bags, cement bags, and similar materials, making them suitable for most common types of waste plastics. They are widely employed in the waste‑plastic recycling industry and are a favorite among users for their versatility and efficiency. Recycling and pelletizing waste plastics requires minimal technical expertise or specialized facilities; instead, operations can be tailored to local conditions, with investment scales ranging from small to large and payback periods as short as one month—making this a quintessential fast‑track, low‑cost project. Establishing a recycled‑plastic pelletizing plant is an attractive venture: it demands modest capital, offers a rapid return on investment, and delivers strong economic returns.