Importance of Moisture Content in Plywood Manufacturing Process

Wood is a hygroscopic substance, meaning it can exchange moisture with air. Changes in moisture content have an impact on several mechanical characteristics. It is a crucial quality criterion that is sometimes disregarded by many Greenply plywoods makers.

Moisture exchange is affected by the relative humidity and temperature of the air, as well as the amount of water in the wood. This relationship has a significant impact on the qualities and quality of produced plywood.

The Bureau of Indian Standards (BIS) recommends that plywood have a moisture level of 5% - 15% by weight. Moisture content that is above or below this range can have a negative impact on produced items and the environment.

Some of the factors that are impacted by variations in moisture content are as follows:

Glue consumption

In the plywood business of green MDF, drying is a procedure used to minimize the moisture level of core veneers. It is a critical procedure that must be constantly monitored since it directly affects the quality of plywood. Companies in general do not place a high value on this procedure and often dry the veneers for a longer period of time, resulting in a condition known as surface inactivation or case hardening. It is a condition in which all of the moisture at the molecular level of the wood evaporates, rendering the cell walls inactive. This inactivation has a significant impact on veneer glue use.

Glue is composed of approximately 50% solid material and 50% moisture. When inactivated veneer comes into touch with this adhesive, it absorbs a significant amount of moisture from the glue, resulting in a shorter flow time. As a result, the veneers absorb a greater volume of adhesive. As a result, the price of plywood rises overall.

If the moisture content is optimum, the cell walls of veneers are not inactivated and still contain some moisture. As a result, the adhesive has a longer flow time and hence consumes less.

Mechanical Properties

Mechanical qualities like bending strength, shear strength, and modulus of elasticity are significant characteristics for determining the quality of plywood. These requirements guarantee that plywood may be used for an extended period of time without failing.

According to studies, the value of these qualities is inversely related to the moisture level of veneers. The higher the moisture level, the lower the strength.

Thickness Variation

The maximum thickness difference seen at different spots on the plywood is referred to as thickness variation. Plywood with less thickness fluctuation is thought to be of higher quality.

The drying of core veneers is critical in limiting the variances in plywood thickness. As a veneer dries, it loses moisture and shrinks as a result. Wavy veneers result from prolonged drying. When these wavy veneers and crossbands are pressed in the hot press, they begin to straighten, resulting in gaps and overlaps in plywood. The thickness varies as a result of these gaps and overlaps.

Visual Defects

Failing to control the moisture content can also lead to visual defects in Greemply plywoods. Some of the visual defects can be as follows –

a. Air pockets

Air pockets are lumps and fissures on the face veneer created by vapours released from the core veneers. This happens when the moisture level of the veneers is high. When heat pressed, the moisture in veneers begins to evaporate in the form of vapours. These vapours become trapped between the core and face veneers, resulting in air pockets and fissures.

b. Face cracking

Face cracking is commonly caused by the high moisture content of the face veneer. When a damp face veneer is a heat pressed, it begins to lose moisture and flex fast. As a result, it cracks in areas.

All of these variables underline the significance of moisture content in the manufacture of plywood.

Plywood products by green MDF are manufactured with the highest regard for moisture content. The items are created using high-quality raw materials, and quality requirements are upheld at every stage of the manufacturing process.