ORIGINALS ORIGINALARBEITEN

Processing and flexural properties of surface reinforced flatpressed WPC panels

Henrik Schmidt • Jan T. Benthien •

Heiko Thoemen

Received: 24 August 2012 / Published online: 5 July 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract While extrusion and injection molding are the

common technologies to produce wood-plastic composites

(WPC), pressing may be an alternative, particularly when

flat products are striven for. In this study, flat pressed WPC

panels were surface-reinforced by two different types of

thermoplastic face layers to improve flexural properties. The

two face materials applied were a commingled fabric made

of glass and polypropylene filaments (TWINTEX�) and a

glass fabric reinforced polypropylene laminate (S-TEX�).

Combination of face layers and WPC panels was achieved in

a single and a two stage flat pressing process. Besides

studying the effects of reinforcing material and number of

process stages, the influence on flexural properties of the

reinforced panels was identified. Unreinforced WPC panels

were tested for comparison. The reinforced WPC panels

exhibited greatly improved flexural properties, with MOE

(MOR) values up to nearly 10,000 N/mm2 (90 N/mm2).

Herstellung und Biegeeigenschaften von flachgepressten

WPC-Platten mit verstarkten Deckschichten

Zusammenfassung Holz-Kunststoff-Verbundwerkstoffe

(wood-plastic composites) (WPC) werden uberwiegend im

Extrusions- oder Spritzgießverfahren hergestellt. Alternativ

hierzu konnen plattenformige WPCs mit Hilfe der

Flachpresstechnologie hergestellt werden. In dieser Studie

wurden flachgepresste WPC-Platten mit zwei verschiedenen

thermoplastischen Deckschichtmaterialien verstarkt, um so

deren Biegeeigenschaften zu verbessern. Als Deckschicht-

materialien wurden TWINTEX�, eine kombinierte Glasfa-

ser-Polypropylenfaser-Matte, sowie S-TEX�, eine dunne

glasfaserverstarkte Polypropylenplatte, verwendet. Die

Verbindung zwischen Deckschicht und WPC-Platte wurde

in einem ein- und einem zweistufigen Verfahren realisiert.

Erganzend zum Einfluss des Verstarkungsmaterials und der

Anzahl der Prozessschritte, wurden die Biegeeigenschaften

der verstarkten Platten bestimmt. Als Referenzmaterial dien-

ten unverstarkte WPC-Platten. Durch die Verstarkung der

Deckschichten wurde ein Anstieg der Biegeeigenschaften

auf einen Wert von fast bist zu 10.000 N/mm2 (MOE) und

90 N/mm2 (MOR) erzielt.

1 Introduction

Wood–plastic composites (WPC) are mainly processed into

profiles or 3-dimensional form parts by extrusion and

injection molding techniques. In building applications,

dimensions of WPC profiles and also extruded sheets are

restricted to the limitations of the extruders; therefore only

limited widths and thicknesses can be achieved. Aside from

extrusion and injection molding, flat pressing technology, in

reference to the wood-based panel production, may be seen

as a promising method to manufacture large dimensioned

WPC panels. Various scientific papers deal with the devel-

opment of WPC panels in laboratory scale (Benthien and

Thoemen 2012; Philipp 2005; Wolcott 2003; Boeglin et al.

1997; Falk et al. 1999; Chaharmahali et al. 2008). WPC

panels offer a good alternative to lumber or wood-based

panels because of their durability and low maintenance cost

H. Schmidt � J. T. Benthien (&)

Department of Wood Science, Mechanical Wood Technology,

Hamburg University, Leuschnerstrasse 91c, 21031 Hamburg,

Germany

e-mail: jan.benthien@vti.bund.de

H. Thoemen

Department of Architecture, Wood and Civil Engineering,

Bern University of Applied Sciences, Solothurnstrasse 102,

2500 Biel, Switzerland

123

Eur. J. Wood Prod. (2013) 71:591–597

DOI 10.1007/s00107-013-0719-y

(Rizvi and Semeralul 2008). While the water resistance

properties are advantageous, flexural properties should be

further improved. According to Falk et al. (1999) maximum

bending modulus of elasticity (MOE) of WPC panels is

similar to the lower MOE-ranges of particleboard and

medium-density fiberboard. Maximum bending MOR of flat

pressed WPCs is comparable to the lower modulus of rup-

ture (MOR) range of oriented strand board (OSB). There

have been different attempts to improve the mechanical

properties of flat pressed WPC panels and other WPC

products such as extruded profiles. The properties of WPC

depend on many parameters such as the amount of wood

filler, fiber aspect ratio of the wood particles and the adhe-

sion between wood and polymer (Jiang et al. 2007).

One option to increase the strength and toughness of WPC

products is the addition of glass fiber reinforcement to the

compound. Rizvi and Semeralul (2008) added 5 % glass fibers

to WPC specimen with varying amounts of wood fiber content

and found significant improvement in strength and modulus.

By using an integrated pressing and cooling device and

pretend infrared heating (fusion bonding) Jiang et al. (2007)

applied commingled glass and polypropylene filaments

(TWINTEX�) in form of an unidirectional tape to WPC

deck boards. Arrangements with and without additional

polypropylene tie-layer between the WPC and the thermo-

plastic reinforcement were carried out. Improvement of

MOE and MOR up to 60 % was achieved by applying the

reinforcement on both surfaces of the WPC deck boards.

Commingled glass and polypropylene filaments

(TWINTEX�) have also been used to design a wood–

polypropylene composite. Dai et al. (2004) applied the

thermoplastic reinforcement to a wood floor structure and

reported an improvement in bending strength of 40 %

compared to the unreinforced deck board.

The aim of this study was to determine chances and

limitations of enhancing flexural properties of flat pressed

WPC panels. Reinforced WPC panels were manufactured

with two different thermoplastic fiber-reinforced face

materials using a one-step and a two-step flat pressing

process. The flexural properties of the reinforced panels

were examined and compared to those of unreinforced flat

pressed WPC panels to detect the potential of the different

reinforcement systems to improve flexural properties. The

density of the WPC middle layer was modified to investi-

gate the influence on the properties of the reinforced panels.

2 Materials and methods

2.1 Materials

The polypropylen (PP) (HP 500 V) used for the WPC pro-

vided by Basell Polyolefine GmbH (Lyondell Basell

Industries), Wesseling, Germany, was pulverized by (kryo-)

milling to ensure fine spreading using dry blending as

mixing method. The melt flow rate (MFR) of the polymer is

120 g/10 min (230 �C/2.16 kg).

Soft wood flour JELUXYL WEHO 500S was provided

by JELU-WERK, Rosenberg, Germany. The main mass

fraction of \0.3 mm was determined by sieve analysis.

Before mixing the raw materials, the wood flour (WF) was

ovendried at 105 �C to a moisture content of about 1 %. As

Stark (2001) stated, using WF with high moisture content

adversely affects mechanical properties of the WPCs.

Two different types of thermoplastic reinforcement

materials were used as surface layers. TWINTEX� is a

reinforcement fabric of commingled thermoplastic and

glass filaments provided by Schilgen, Emsdetten, Ger-

many. The material is commonly used in 3-dimensional

and sandwich structures in building, automotive and mar-

ine application. Consolidation of the commingled fibers is

done by heating the fabric above melting temperature of

the polypropylene. The fabric is woven in a 2/2 twill pat-

tern. S-TEX� is a glass fabric reinforced polypropylene

laminate with randomly oriented glass fibers. The ortho-

tropic laminate is commonly used for large semi-structural

applications in a sandwich structure and has a thickness of

approx. 1.5 mm. The material was kindly provided by

Quadrant Plastics, Lenzburg, Switzerland. Properties of the

reinforcement materials are shown in Table 1.

2.2 Methods

The size of all manufactured WPC test panels was 420 mm

in length and 380 mm in width. The WF was manually

mixed with the polymer powder at room temperature (dry

blending method) and placed into a frame made of poly-

urethane (PU) foam to inhibit a lateral yielding of the

dryblend while pressing. When producing a reinforced

panel, the facing material was cut to size and placed within

the PU frame underneath and above the WPC. The target

thickness of all panels was 10 mm. The amount of WPC

material in a reinforced panel was calculated by estimating

Table 1 Properties of S-TEX� and TWINTEX�

Tab. 1 Eigenschaften von S-TEX� und TWINTEX�

S-TEX TWINTEX

Nominal weight (g/m2) 2,178 985

Glass content by weight (%) 40 60

Glass weight (g/m2) 871 591

Tensile strength (N/mm2) 125a 50b

Tensile modulus (N/mm2) 10,200a 4,700b

a Longitudinal directionb Transverse direction

592 Eur. J. Wood Prod. (2013) 71:591–597

123

the thickness of the facing material and the WPC middle

layer in the finished panel.

The pressing of the panels was conducted on a com-

puter-controlled laboratory hot press, whereas cooling took

place in a separate press while keeping the panel thickness

constant by using distance bars. The hot press was operated

in plate position control mode, with the pressure limited to

a maximum of 700 N/cm2. WPC reference panels without

reinforcement and WPC middle layers to be reinforced in a

second process step were hot-pressed for 500 s at 210 �C.

Surface reinforced panels manufactured in a one-step

process were pressed with a pressure of 45 N/cm2 for

400 s, before a specific pressure of 700 N/cm2 was

implemented for another 100 s. The same pressing pro-

gram was used when applying a surface layer to a previ-

ously made WPC middle layer. By applying low pressure

for 400 s, the polymer in the thermoplastic surface lami-

nates and in the WPC-layer plasticized before compression

to the target thickness.

2.3 Experiment design

The WPC consisted of 70 % WF and 30 % PP powder. In

order to identify the influence on the flexural properties of

surface reinforced flat pressed WPC panels, three series (A,

B, C) with altering modifications (type of reinforcement,

density of WPC-layer, number of process stages) were

designed (Table 2). Three test panels for each modification

were pressed and four bending specimens were cut from

each panel.

2.4 Characterization of flexural properties

Three-point bending tests according to DIN EN 310:1993

were carried out to investigate MOE and MOR. For

homogeneous materials such as unreinforced WPC panels,

three-point bending leads to constant results independent of

panel thickness. In multilayered panels of different thick-

nesses, changing amounts of shear strain lead to inconsis-

tent values of MOE and MOR (Gupta 2007). Therefore, the

experimental values only apply to the specific panel setup

and thickness. To be able to compare the panels and

evaluate the influence of the different types of reinforce-

ment, density of WPC layer and number of process stages,

a consistent panel thickness for all manufactured panels

was of great importance.

3 Results and discussion

3.1 Influence of surface reinforcement type

Table 3 summarizes the average values of MOE and MOR

of the reinforced panels and unreinforced reference panels

(series A). The reinforced WPC panels show greatly

improved flexural properties in comparison to the unrein-

forced reference panels. The reinforcement with TWIN-

TEX� in a single step process leads to a 2.4 (4.0) times

higher MOE (MOR) compared to the unreinforced refer-

ence panel. Surface reinforced panels using S-TEX� show

3.4 (5.6) times higher MOE (MOR). For comparision,

Boehme (1976) found for glass fiber/polyester resin rein-

forced particleboards with a thickness of 10.7 mm (8 mm

core layer thickness) flexural properties of 6,011 N/mm2

(61.3 Mp/cm2) (MOE) and 81.2 N/mm2 (MOE/

MOR = 74) (MOR), and Cai (2006) found for glass fiber/

phenol resin reinforced medium-density fiberboards,

respectively flakeboards (12.7 mm core layer thickness)

flexural properties of 3,310 N/mm2 (3.31 GPa) (MOE) and

33.4 N/mm2 (33.4 MPa) (MOR), respectively 7,140 N/

mm2 (7.14 GPa) (MOE) and 51.3 N/mm2 (51.3 MPa)

(MOR).

S-TEX� reinforced WPC panels show higher values

than panels reinforced with TWINTEX� due to the higher

glass fiber content and the higher nominal weight of the

Table 2 Test set-up with different modifications of materials, den-

sities and process parameters

Tab. 2 Versuchsaufbau mit Blick auf Material, Dichte und

Prozessparameter

Series Type of

reinforcement

WPC density

(g/cm3)

Number of

process steps

A Unreinforced 0.8 1

TWINTEX� 0.8 1

S-TEX� 0.8 1

B Unreinforced 0.65 1

Unreinforced 0.8 1

TWINTEX� 0.65 1

TWINTEX� 0.8 1

S-TEX� 0.65 1

S-TEX� 0.8 1

C TWINTEX� 0.8 1

TWINTEX� 0.8 2

S-TEX� 0.8 1

S-TEX� 0.8 2

Table 3 Mean values of flexural properties of the different rein-

forced panels and unreinforced panels (n = 12)

Tab. 3 Mittelwerte der Biegeeigenschaften der unterschiedlich

verstarkten bzw. unverstarkten Platten (n = 12)

Unreinforced TWINTEX� S-TEX�

MOE (N/mm2) 2,828 ± 215.3 6,677 ± 148.5 9,694 ± 736.6

MOR (N/mm2) 15.6 ± 3.0 62.2 ± 4.1 89.7 ± 9.4

Eur. J. Wood Prod. (2013) 71:591–597 593

123

material. S-TEX� shows 40 % glass content by weight

which calculates to 871 g glass fibers, while the TWIN-

TEX� fabric contains 591 g of glass fibers per square

meter. Because S-TEX� surface layer is estimated to have

a thickness of 1.7 mm after pressing, the WPC panel is

correspondingly thin to form a panel with the overall

thickness of 10 mm. This leads to a predominant influence

of the reinforcing material on the properties of the whole

reinforced panel. TWINTEX� is estimated to have a

thickness of 0.7 mm in the manufactured composite panel.

For further characterization of the surface materials as

reinforcement for flat pressed WPC panels, fracture char-

acteristics of the composites in addition to absolute

strength values are analyzed.

In Fig. 1 exemplary load-displacement curves for two

different reinforced panels and an unreinforced panel

obtained from three-point bending are presented. It can be

seen that the unreinforced panel failed with a brittle frac-

ture while both surface reinforced WPC panels showed

ductile fracture behavior after reaching the maximum load.

Hereby the TWINTEX� reinforced WPC panel showed a

more extensive ductility and flexibility than the S-TEX�

reinforced panel, as can be seen in the bigger displacement.

Since the testing machine was set up to stop bending when

the load-level of the decreasing load curve reached a value

of 90 % of the maximum load, the testing procedure for the

TWINTEX� panels was often stopped manually, because

the 10 % drop of the load took several minutes and total

failure of the specimen did not occur.

In Fig. 2 the fracture patterns of exemplary bending

specimens are presented. In Fig. 2a, wrinkling on the top-

side of a TWINTEX� reinforced panel can be observed.

All specimens of this type showed wrinkling on the top-

side. Total failure never occurred and the bottom of the

specimen which was exposed to tensile strain stayed

visually intact. Figure 2b shows the tensile fracture of an

S-TEX� reinforced WPC panel. These types of reinforced

panel failed mostly by tensile fracture or to a lesser extent

by shear fracture in the middle of the WPC-layer (Fig. 2c).

Shear failure or tensile fracture occurs in the S-TEX�

reinforced WPC panels, because the STEX� laminates

show high compressive strength. Therefore, no stress is

compensated by local wrinkling on the topside of the

composite. Consequently tensile and shear stress increases

and leads to failure. In the TWINTEX� reinforced panel no

shear fracture is observed. The TWINTEX� layers are thin

and wrinkle when exposed to pressure. Thus TWINTEX�

reinforced panels show smaller flexural strengths but no

total failure by tensile fracture, whereas S-TEX� rein-

forced panels reach higher values but fail with tensile or

shear fracture. Both reinforced panel types show no

delamination of the surface layer while exposed to bending.

Strong interfacial adhesion and a good compatibility

between the matrix polymers of the face materials and the

thermoplastic in the WPC are indicated.

3.2 Influence of the WPC layer density

The density of the WPC layer was regulated by the weight

of the raw materials. Pressing parameters were kept con-

stant for both target densities. The panels included in the

investigation on the influence of the density of the WPC-

layer were all manufactured in a single stage process. As

can be seen in Fig. 3, the increase in density of 0.15 g/cm3

leads to about two times higher MOE and MOR values for

the unreinforced panels. Benthien et al. (2009) state that the

density of the WPC panels is the strongest influencing

factor on physical and mechanical properties. For the

reinforced panels improvements of flexural values with

increasing density of the WPC-layer are less extensive.

MOE of the TWINTEX� reinforced panel increases by

13 %, MOR by 30 % when WPC density rises from 0.65 to

Fig. 1 Load-displacement curves of the different types of reinforced

panels

Abb. 1 Kraft-Wegdiagrammkurven der unterschiedlichen verstark-

ten Platten

Fig. 2 Fracture-characteristics of the WPC panels reinforced with

a TWINTEX� and b, c S-TEX�

Abb. 2 Bruchcharakteristiken der mit a TWINTEX� und b, c S-

TEX� verstarkten WPC-Platten

594 Eur. J. Wood Prod. (2013) 71:591–597

123

0.80 g/cm3. 0.15 g/cm3 raise in density leads to an increase

of MOE by 10 % and MOR by 27 % for S-TEX� rein-

forced panels. Fracture pattern of the reinforced panels

with low density core layers is mainly wrinkling on the top

side of TWINTEX� reinforced panels, while S-TEX�

reinforced panels all fail by shearing in the middle of the

WPC layer. Unlike the S-TEX� reinforced panels with

higher WPC density, no tensile fracture of the bottom

S-TEX� surface layer occurred. Increase of MOR with

rising WPC density is stronger than the increase of MOE

for both reinforced panel types. This can also be observed

by looking at the correlation between overall density of the

reinforced panels with MOE and MOR in Fig. 4. Properties

of TWINTEX� and S-TEX� reinforced panels increase in

a similar linear manner with rising WPC density. The

effect of the MOE of the WPC is less influential on the

MOE of the reinforced panels than the MOR of the WPC

on the MOR of the reinforced panels.

The reason for this behavior can be found in the rela-

tionship between MOE and MOR (MOE/MOR) of the

different materials. While the ratio in unreinforced WPC

panels is very high (170…200), the ratio between MOE

and MOR for the S-TEX� material itself is rather low (30).

The reinforced panels show a ratio between 85 and 120.

Therefore, the reinforcement generally shows a stronger

influence on MOR than on MOE. Albers and Plath (1970)

and also Boehme (1976) found the same phenomena for

surface reinforced wood-based panels.

3.3 Influence of number of process stages

Besides the obvious economic differences of a single stage

and a two-step process to manufacture surface reinforced

WPC panels, properties also change with the number of

process steps. As can be seen in Fig. 5, MOE is higher for

the reinforced panels, which are manufactured in a single

process step, while MOR is higher for the panels which are

manufactured in a two step process.

This behavior can be explained by the different density

profiles over the cross section of the panels, which develop

in the progression of the pressing process. It can be

examined that the single stage process leads to a region of

very high density of the WPC directly beneath the rein-

forcing S-TEX� material. This may be caused by a prec-

edent densification of this region due to a higher specific

pressure. The additional reinforcement supplies more

material which needs to be compressed. The pressure is at

first transmitted to the WPC layer until the polymer of the

laminate plasticizes. The density profiles shown in Fig. 6

further indicate that the single stage process leads to a

redistribution of the polymer of the reinforcement layers.

Especially the S-TEX� reinforced panels show a dis-

similar density distribution on the surface of the reinforced

panels. In the single stage process the reinforcement is

plasticized by the heat of the press plates before the plas-

ticization of the polymer in the WPC layer starts. A part of

the polymer of the reinforcement flows into the not yet

Fig. 3 Influence of core density

on MOE and MOR of the

reinforced panels

Abb. 3 Einfluss der

Kernschichtdichte auf MOE und

MOR der verstarkten Platten

Fig. 4 Correlation between

panel density and flexural

properties

Abb. 4 Korrelation zwischen

Plattendichte und

Biegeeigenschaften

Eur. J. Wood Prod. (2013) 71:591–597 595

123

plasticized WPC layer parallel to the direction of the heat

transfer. Consequently, because a part of the polymer of the

face material flows to the middle, the reinforcing glass

fabric in the surface material moves further to the surface

of the panels. The higher density values on the surface of

the S-TEX� may be caused by the accumulation of the

glass fibers due to the flow-off of the polymer. This mod-

ification as well as the oriented structure (woven) and the

Fig. 5 Flexural properties

depending on the number of

process steps

Abb. 5 Biegeeigenschaften in

Abhangigkeit der Anzahl der

Prozessschritte

Fig. 6 Density profiles of the

reinforced panels manufactured

in a single and two stage

process, left TWINTEX, right

S-TEX�

Abb. 6 Rohdichteprofile der

verstarkten Platten, die im

einstufigen und zweistufigen

Prozess hergestellt wurden.

Links: TWINTEX�, rechts:

S-TEX�

Fig. 7 Cross-sections of the

differently manufactured panels,

a S-TEX�: single stage process,

b S-TEX�: two stage process,

c TWINTEX�: single stage

process, d TWINTEX�: two

stage process

Abb. 7 Querschnitte der

unterschiedlich hergestellten

Platten. a S-TEX�: einstufiger

Prozess, b S-TEX�:

zweistufiger Prozess,

c TWINTEX� einstufiger

Prozess, d TWINTEX�:

zweistufiger Prozess

596 Eur. J. Wood Prod. (2013) 71:591–597

123

higher amount of glass fibers (see Table 1) lead to higher

MOE. The reinforced panel on the other hand, which is

manufactured in a two stage process, shows a broader

range of high density over the width of the reinforcement

layer. No flow-off into the WPC-layer takes place, since

the reinforcing material is pressed on an intact WPC sur-

face that does not draw in plasticized polymer as much as

the unconsolidated dryblend. These panels show higher

MOR. In Fig. 7 images of the cross sections of the dif-

ferently manufactured reinforced panels are displayed. It is

well recognizable that the S-TEX� and TWINTEX�

reinforcement layers are thinner when combined with the

WPC layer in a single stage process (Fig. 7a, c), while the

reinforcement layers in panels manufactured in a two stage

process stay intact with no flow-off of the matrix-polymer

(Fig. 7b, d).

4 Conclusion

Two different types of thermoplastic reinforcement-sys-

tems were used to enhance the flexural properties of flat

pressed WPC panels. The utilized materials were a com-

mingled fabric made of glass and polypropylene filaments

(TWINTEX�) and a glass fabric reinforced polypropylene

laminate (S-TEX�). The compatibility of the polymer-

systems of both reinforcement materials with the WPC was

found to be very satisfying. Delamination between the

layers did not occur for both types of reinforced panels. Up

to 5.6 times higher MOR and 3.4 times higher MOE were

achieved in comparison to unreinforced WPC panels.

S-TEX� reinforced panels showed higher flexural proper-

ties than TWINTEX� reinforced panels because of higher

nominal weight and glass content. Fracture behavior of the

reinforced panels was dissimilar. S-TEX� panels failed

either by tensile break or by shear fracture, caused by the

high compressive strength of the reinforcing layer.

TWINTEX� panels showed wrinkling on the compressed

top side of the panel, which was promoted by the minor

thickness of the layer and therefore did not fail by tensile

fracture or shear fracture. The different fracture patterns

and the related ductile fracture behavior visualized by the

slowly decreasing load displacement curves (Fig. 1)

obtained by three-point bending indicate another advantage

of the reinforced panels. Besides the extensively increased

flexural properties the fracture behavior changed from a

brittle manner to a distinct ductility, which further pro-

motes the suitability of the reinforced WPC panels in

structural applications.

References

Albers K, Plath E (1970) Festigkeitseigenschaften beplankter Holz-

werkstoffe. Holz-Zent bl 96:41–42

Benthien J T, Thoemen H, Weissmann V, Korte H (2009) WPC-

Herstellung nach dem Flachpressverfahren: Einfluss der Roh-

stoffkomponenten und Herstellungsparameter auf die physika-

lischen und mechanischen Eigenschaften. 3rd german WPC

conference, Cologn, 2–3 Dezember 2009

Benthien JT, Thoemen H (2012) Effects of raw materials and process

parameters on the physical and mechanical properties of flat

pressed WPC panels. Compos Part A 43(4):570–576

Boeglin N, Triboulot P, Masson D (1997) A feasibility study on boards

from wood and plastic waste: bending properties, dimensional

stability and recycling of the board. Holz Roh-Werkst 55(1):

13–16

Boehme C (1976) Constructive behavior of Gfk-wood sandwiches—

comparison of experimental results with various computation,

methods. Holz Roh Werkst 34(5):155–161

Cai Z (2006) Selected properties of MDF and flakeboard overlaid

with fiberglass mats. Forest Prod J 56(11/12):142–146

Chaharmahali M, Tajvidi M, Kazemi Najafi S (2008) Mechanical

properties of wood plastic composite panels made from waste

fiberboard and particleboard. Pol Compos 29(6):606–610

Dai HM, Smith MJ, Ramani K (2004) Design and processing of a

thermoplastic composite reinforced wood structure. Polym

Compos 25(2):119–133

DIN EN 310 (1993) Holzwerkstoffe; Bestimmung des Biege-Elasti-

zitatsmoduls und der Biegefestigkeit

Falk RH, Vos DJ, Cramer SM (1999) The comparative performance

of woodfiber-plastic and wood based panels. In: Rowell R (ed)

5th International Conference on Woodfiber-Plastic-Composites,

Madison, pp 269–274

Gupta N (2007) Response of syntactic foam core sandwich structured

composites to three-point bending. J Sandwich Struct Mate

4(3):249–272

Jiang L, Wolcott MP, Zhang JW et al (2007) Flexural properties of

surface reinforced wood/plastic deck board. Polym Eng Sci

47(3):281–288

Philipp K (2005) Flachgepresste Holz-Kunststoff-Verbundwerkstoffe.

Diploma Thesis. University of Hamburg, Germany

Rizvi GM, Semeralul H (2008) Glass-fiber-reinforced wood/plastic

composites. J Vinyl Add Tech 14(1):39–42

Stark N (2001) Influence of Moisture Absorption on Mechanical

Properties of Wood Flour–Polypropylene Composites. J Ther-

moplast Compos Mater 14(5):421–432

Wolcott MP (2003) Formulation and process development of flat-

pressed wood-polyethylene composites. For Prod J 53(9):25–32

Eur. J. Wood Prod. (2013) 71:591–597 597

123