Filler is a substance that is added to plywood glue to improve its properties and reduce its cost. Filler can be organic, such as flour, wood powder, or bark powder, or inorganic, such as calcium carbonate, aluminum oxide, or bentonite. Filler can affect the viscosity, curing speed, water resistance, and formaldehyde emission of the glue. Different types of plywood require different types of filler.
Some of the most common types of filler used in plywood manufacturing are:
Flour: This is a type of organic filler that is made from wheat, rice, or corn. It is cheap and easy to obtain, and it can improve the bonding strength and water resistance of the glue. However, it can also increase the formaldehyde emission and the susceptibility to fungal and borer attacks. Flour is often used for interior plywood, such as furniture or cabinets.
Wood powder: This is a type of organic filler that is made from sawdust, wood chips, or wood shavings. It is a by-product of wood processing, and it can reduce the cost and increase the wood content of the glue. However, it can also reduce the bonding strength and water resistance of the glue, and it can cause uneven color and texture of the plywood. Wood powder is often used for low-grade plywood, such as packing or construction plywood.
Bark powder: This is a type of organic filler that is made from tree bark, which is usually discarded as waste. It is a renewable and eco-friendly resource, and it can improve the viscosity and water resistance of the glue. However, it can also reduce the bonding strength and increase the formaldehyde emission of the glue, and it can cause dark spots and rough surface of the plywood. Bark powder is often used for exterior plywood, such as siding or roofing plywood.
Calcium carbonate: This is a type of inorganic filler that is made from limestone, marble, or chalk. It is widely available and inexpensive, and it can improve the viscosity and curing speed of the glue. However, it can also reduce the bonding strength and water resistance of the glue, and it can cause cracking and delamination of the plywood. Calcium carbonate is often used for interior plywood, such as furniture or flooring plywood.
Aluminum oxide: This is a type of inorganic filler that is made from bauxite, corundum, or alumina. It is a hard and abrasive material, and it can improve the bonding strength and water resistance of the glue. However, it can also increase the cost and the wear and tear of the equipment, and it can cause roughness and brittleness of the plywood. Aluminum oxide is often used for high-performance plywood, such as marine or aircraft plywood.
Bentonite: This is a type of inorganic filler that is made from clay, which is rich in montmorillonite. It is a soft and sticky material, and it can improve the viscosity and water resistance of the glue. However, it can also reduce the bonding strength and increase the formaldehyde emission of the glue, and it can cause swelling and shrinking of the plywood. Bentonite is often used for moisture-resistant plywood, such as exterior or laminated plywood.