What are the differences and characteristics of vegetable fillers in wood-plastic products

I recycled thermoplastic polymers have a long history of combinations with fillers and fibers, which improve the physical-mechanical performance of the products made using these compounds.

The modifications that we can most notice from the union of a recycled thermoplastic polymer with fillers, may concern the resistance to bending, compression, impact, cutting, abrasion, temperature, ageing, the action of UV rays. and, of course, the recyclability of the element.

What is a thermoplastic polymer?

By recycled thermoplastic polymer, very briefly, we mean an element, of petroleum origin, which softens in the presence of a heat source (extrusion, molding, blow molding or other processing methods) and solidifies on cooling, having a linear or branched polymer chain arrangement.

The behavior of the molecules and their strength determine their characteristics which, in turn, are influenced by the processing or environmental temperatures to which the polymer is subjected.

What is a fiber or vegetable filling?

The fibers are filaments with a precise ratio between length and diameter, which allow the improvement of the characteristics of a compound in which they are incorporated, by replacing the volume of the primary material, so as to increase its toughness and flexibility.

The fibers, in general, can be of three categories: inorganic, organic or natural. The first, among the most commonly used in polymer compounds, they are based on glass, carbon, graphite, aluminum. Among the organic fibers we can mention polyamides and polyolefins. As for the natural fibers we can divide them into three categories: vegetable, animal and mineral.

The purpose of using fibers is to improve the following characteristics:

- the mechanical resistance

- the elastic modulus

- the elastic behavior at failure

- the reduction of the specific weight

The fibers are then classified according to physical elements, such as length, thickness, shape, finish and volumetric distribution.

To achieve an improvement in the technical performance of the compound, the surfaces of the fibers will have to adhere completely with the polymeric matrix, so as to create a continuity of material.

Such is the importance of this fiber-polymer union, that additives have been studied that can increase and facilitate the surface contact of each individual fiber with the matrix polymeric.

Even the arrangement of the fibers is critical for the characteristics of the composite. The mechanical properties of a composite with continuous and aligned fibers are strongly anisotropic.

The reinforcement and the consequent resistance reach the maximum value in the alignment direction and the minimum in the transversal direction.

In fact, along this direction the strengthening effect of the fibers is practically nil and, normally, exhibit fractures for relatively low tensile load values. For other load orientations, the overall strength of the composite assumes intermediate values.

In the production of WPC (wood plastic composit), therefore, two elements are used which are represented by a recycled plastic polymer, such as HDPE or LDPE or PVC and vegetable fiber made from wood processing waste or natural vegetable fibers.

Based on the quality, resistance, color and size of the artifacts to be made, it is possible to use a simple filling made up of sawdust, rather than wood flour, wood or cellulose.

The choice of recycled polymer, on the other hand, is also influenced by the operating temperatures of the extruders, which must not thermally ruin the vegetable fillers and, at the same time, degrade the polymer that will remain the glue and the supporting structure of the product.

The production of the WPC takes place by extrusion or moulding, through the use of a plastic granule, which contains the charge established for the production of a specific product and in the planned quantities.

In addition to the wood fiber made up of sawdust or wood flour, it is possible to make more performing compounds using hemp vegetable fiber, normally arranged along the direction line of greater efforts.

Photo Gla floors

Automatic translation. We apologize for any inaccuracies. Original article in Italian.