A membrane sheet (also called a membrane leaf) is one of the core filtration units in reverse osmosis (RO), nanofiltration (NF), or ultrafiltration (UF) systems. It is made by processing membrane material into thin sheets or rolled sheets, used in water treatment systems to retain impurities, salts, or organic substances. A membrane sheet typically consists of the following layers:
- Active Layer: Directly responsible for selective separation, determining the salt rejection rate or the ability to remove contaminants.
- Support Layer: Provides mechanical support for the membrane, ensuring it is not damaged under operating pressure.
- Backing Layer: Enhances structural stability, facilitating rolling or installation into the membrane housing.
Membrane sheets usually undergo processes such as cutting, rolling, and edge sealing to form membrane elements that can be directly installed into housings. Simply put, they are the "core filtration components" of a water treatment membrane system.
So how is a membrane sheet manufactured?
We've prepared a concise flowchart of the membrane sheet manufacturing process to help you quickly understand the production steps and key techniques.
The manufacturing of a reverse osmosis (RO) membrane sheet is a precise and systematic process, designed to ensure high performance and durability. The process can be summarized in several main steps:
First, raw and auxiliary materials, such as polysulfone granules, are purchased and used only after passing quality inspection. Polysulfone, dimethylacetamide (DMAc), and methyl cellosolve are then added to a mixing tank in a specific ratio, forming a casting solution once fully dissolved. Air bubbles are removed from the solution using a vacuum pump or natural degassing. The casting solution is then applied to a nonwoven fabric support layer using a casting machine, and the coated support layer is immersed in a water tank, allowing the solution to gel and form a polysulfone-based membrane. During this process, the water in the tank is periodically recycled through a DMAc recovery system.
The gelled membrane is washed with pure water to remove residual organic solvents and air-dried. Next, the polysulfone-based membrane is wound using the casting machine and loaded onto a coating machine, where dissolved m-phenylenediamine and trimesoyl chloride are added to form an ultra-thin polyamide desalination layer on the membrane. After coating, the membrane is placed in an oven to remove organic solvents, with waste gases treated via a catalytic combustion device. The membrane then enters a post-treatment tank for cleaning, glycerol is applied to protect the surface, and it is subsequently dried in an oven. Finally, the membrane is wound to form the finished RO membrane. This process ensures high salt rejection performance and long service life, providing a reliable core component for water treatment systems.
