How to Increase Wood Flour Content in NFC & WPC Products

Can your WPC product contain more wood flour?

This is a common question for manufacturers of Wood-Plastic Composites (WPC) and Natural Fiber Composites (NFC).

At first, the idea sounds simple:

Use less plastic and add more wood flour.

However, once the wood flour loading starts to increase, manufacturers may experience:

• Higher motor current
• Increased torque
• Poorer melt flow
• Uneven wood flour dispersion
• Rough product surfaces
• Bubbles or internal voids
• Lower extrusion output
• Unstable mechanical properties

Therefore, the real question is not:

How much more wood flour can we add?

The better question is:

How can we increase wood flour content while maintaining stable extrusion and acceptable product performance?

The answer involves the wood flour, polymer, formulation, additives and extrusion equipment.

Why Does High Wood Flour Content Become More Difficult to Process?

In WPC and wood-filled NFC materials, the molten polymer needs to surround, wet and bind a large number of wood particles.

As wood flour content increases:

More wood flour
→ Less polymer per wood particle
→ More difficult polymer wetting
→ Poorer material flow
→ Higher processing resistance
→ More difficult extrusion

The central challenge is therefore:

How can a limited amount of polymer effectively disperse and bind a larger amount of wood flour?

If you are trying to increase the wood content of your current product, the following factors should be checked first.

1. Is Your Wood Flour Dry Enough?

Wood flour is hygroscopic and easily absorbs moisture from the surrounding environment.

When wet wood flour enters the extruder, the moisture can become vapor during processing.

This may cause:

• Surface bubbles
• Internal voids
• Silver streaks
• Rough surfaces
• Density variation
• Unstable extrusion pressure

The higher the wood flour content, the more important moisture control becomes.

A more reliable approach is usually:

Pre-drying
+
Controlled storage
+
Vacuum venting

If bubbles suddenly become more serious after increasing wood flour content, moisture and venting should be among the first things to check.

2. Is Finer Wood Flour Always Better?

No.

Finer wood flour can improve surface uniformity in some products.

However, smaller particles also create a larger total surface area.

This means:

The polymer has more wood surface to wet and cover.

Particle-to-particle interaction can also increase.

Therefore, the target should not simply be:

The finest possible wood flour

but rather:

A suitable and stable particle-size distribution for the polymer and extrusion system.

3. Are the Wood Flour and Polymer Really Bonding?

This becomes increasingly important at higher wood loadings.

Wood flour is naturally hydrophilic, while polymers such as PE and PP are relatively hydrophobic.

In simple terms:

Wood and plastic do not naturally bond very well.

Poor interfacial compatibility may cause:

• Agglomeration
• Incomplete polymer wetting
• Internal gaps
• Reduced strength
• Higher water absorption

The higher the wood content, the more important this interface becomes.

4. Why Are Additives Important for High Wood Flour Formulations?

As wood flour loading continues to increase, a conventional formulation may approach its processing limit.

A common situation is:

More wood flour
→ Poorer flow
→ Higher current and torque
→ Unstable extrusion

For this reason, an additive for high wood flour processing should do more than provide simple lubrication.

An effective system should help improve:

• Wood flour dispersion
• Polymer wetting
• Processing flow
• Interfacial behavior
• Extrusion stability

This is one of the reasons we developed our PWG Additive.

5. PWG Additive: Developed for Higher Wood Flour Loading

In practical NFC/WPC production, we have found that many manufacturers can technically add more wood flour.

The real limitation is often:

The material becomes too difficult to process consistently.

Our PWG additive was developed specifically around this challenge.

Rather than simply adding another lubricant to the formulation, PWG is designed to support the overall processing behavior of high wood flour composites.

Depending on the formulation and processing conditions, PWG can help support:

Higher Wood Flour Loading

Helping the formulation remain processable as the wood flour content increases.

Improved Material Flow

Reducing some of the processing difficulties associated with highly filled compounds.

Better Wood Flour Dispersion

Helping reduce local agglomeration and uneven material distribution.

More Stable Extrusion

Supporting more consistent processing when higher wood loading affects current, pressure and output stability.

More Effective Wood/Polymer Interaction

Helping the polymer work more effectively within a highly wood-filled composite system.

Actual performance depends on factors including:

• Polymer type
• Wood flour source
• Particle size
• Moisture content
• Existing additives
• Extruder configuration
• Final product requirements

For this reason, we prefer to evaluate the actual formulation instead of recommending one fixed dosage for every customer.

Has Your Wood Flour Content Reached a Processing Limit?

Ask yourself:

Does motor current rise sharply when you increase wood flour?

Does extrusion output start to fall?

Does the product surface become rougher?

Does die pressure become unstable?

Do bubbles or internal voids appear?

Do mechanical properties decline after adding more wood flour?

If several of these problems occur together, your current formulation + extrusion system may be approaching its practical processing limit.

At this point, simply adding more wood flour is unlikely to solve the problem.

A better approach is to evaluate:

Raw Materials + Additives + Processing + Equipment

together.

6. More Lubricant Is Not Always the Answer

When a high wood flour compound becomes difficult to process, adding more lubricant may seem like the easiest solution.

It may improve flow in the short term.

However, excessive lubrication may also affect the interaction between the wood flour and polymer.

The target should therefore not be:

More lubricant

but:

A better-balanced processing system.

PWG was developed with this broader processing objective in mind rather than focusing only on friction reduction.

7. Extrusion Equipment Also Determines the Practical Wood Flour Limit

Even with a well-designed formulation, the extruder remains critical.

High wood flour compounds typically combine:

High filler loading + High processing resistance + Limited flowability + Thermal sensitivity

Important equipment factors include:

Stable Feeding

Higher wood content changes bulk density and material flow behavior.

Unstable feeding can result in:

Output variation → Pressure variation → Product dimension variation

Sufficient Torque

When processing highly filled composites, manufacturers should look beyond only:

kg/h

and also consider:

• Torque
• Motor load
• Screw speed
• Plasticizing capacity
• Operating stability

Proper Screw Design

Maximum shear is not the objective.

The correct balance is:

Feeding → Plasticizing → Mixing → Venting → Metering

8. Do Not Ignore Vacuum Venting

More wood flour means more natural material capable of carrying moisture and volatile components into the process.

Poor venting can cause:

• Bubbles
• Internal voids
• Surface defects
• Density variation

For high wood flour extrusion:

Drying + Vacuum Venting

is usually more reliable than depending on only one of them.

9. Do Not Solve Every Flow Problem by Increasing Temperature

Higher temperature can reduce the viscosity of many thermoplastics.

However, wood flour is thermally sensitive.

Excessive temperature or residence time may lead to:

• Discoloration
• Charring
• Odor
• Increased volatiles
• Product color variation

If the material becomes difficult to process after increasing wood flour, continuously raising the temperature is therefore not an ideal solution.

The formulation, additives and extrusion parameters should be evaluated together.

10. How Should Higher Wood Flour Content Be Tested?

We recommend increasing wood flour gradually.

A practical test procedure is:

Current Stable Formulation

↓

Introduce PWG and optimize the base formulation

↓

Increase wood flour gradually

↓

Monitor motor current and torque

↓

Check die pressure

↓

Inspect surface and internal structure

↓

Test mechanical properties

↓

Continue optimization

Important parameters include:

The objective is to find the balance between:

Higher wood flour content and stable product performance.

Is More Wood Flour Always Better?

No.

The most useful target is not simply:

Maximum Wood Flour Content

It is:

Maximum Stable Wood Flour Content

In other words:

The highest practical wood flour loading that still allows stable production and meets the required product performance.

Different factories use different:

• Wood flour
• PE, PP or PVC
• Equipment
• Product designs
• Dies
• Performance requirements

There is no single percentage that applies to every product.

Want to Know Whether Your Product Can Use More Wood Flour?

If you currently manufacture:

• WPC boards
• WPC profiles
• Wood/PE composites
• Wood/PP composites
• Wood/PVC composites
• Other NFC products

and want to increase the wood flour content, send us:

1. Current wood flour percentage
2. Polymer type — PE, PP, PVC, etc.
3. Wood flour particle size
4. Main additives currently used
5. Product dimensions and application
6. Extruder model and output
7. Problems encountered after increasing wood flour

Our engineering team can use this information to assess:

Is the main limitation coming from the formulation or from the extrusion system?

We can then evaluate whether PWG Additive is suitable for your material system.

Conclusion

Increasing wood flour content in an NFC or WPC product is not simply a matter of adding more filler.

A stable high wood flour process requires the correct combination of:

Wood Flour

+

Polymer

+

Additives

+

Extrusion Process

+

Equipment

Our PWG Additive was developed for high wood flour composite processing, with the objective of helping manufacturers achieve higher wood loading while maintaining practical extrusion stability.

If your current challenges include:

limited wood loading, excessive motor current, poor flow, rough surface quality or reduced output

send us your current formulation and product requirements.

We can evaluate your formulation and explore how much further your wood flour content can go.

FAQ

Which natural fiber materials can be used in NFC/WPC products?

Potential raw materials include wood flour or wood fibers, crop straw such as wheat straw, rice husks and rice straw, reed fibers, and bamboo flour or bamboo fibers. NFC is the broader term for natural fiber composites; WPC typically refers to wood-based composites.

These materials cannot always be substituted directly for one another. Moisture content, particle size, fiber shape and composition can affect processing and product performance. Each material should be properly cleaned, dried and sized, then evaluated with the selected polymer, additive system and extrusion process.

Tell us which local raw material you would like to use and what product you plan to manufacture. Contact our team to discuss formulation trials and whether PWG Additive is suitable for your material system.

What types of WPC formulations can PWG be used with?

Suitability depends on the polymer, wood flour, existing additives and processing conditions. PE-, PP- and PVC-based systems should be evaluated according to their actual formulation.

How much can PWG increase the wood flour content?

There is no single percentage that applies to every product.

The practical limit depends on the polymer, wood flour particle size, extrusion equipment, product structure and required mechanical properties.

The objective is to increase the wood flour content while maintaining stable production and acceptable product performance.

Can PWG alone solve a high wood flour processing problem?

PWG can help optimize high wood flour processing, but moisture control, particle size, extrusion equipment, screw configuration, venting and processing parameters remain important.

We therefore treat PWG as part of a complete processing solution.

Can you evaluate our existing formulation?

Yes. Provide your current material system, wood flour percentage, product type, extrusion parameters and the main problems you are experiencing.

This helps determine whether the next optimization should focus on the formulation, PWG additive or extrusion process.