Development of Wood Fiber-

Polypropylene Laminates with Layer-

By-Layer Assembly of Kraft Pulp Hand-

Sheets and Polypropylene Films

Todd Shupe and Chung Hse

SWST International Convention

June 7-12, 2015

Grand Teton National Park, WY

Objective

This study examined the effects of

polypropylene (PP) film thickness, hand-

sheet fiber content in layer (FC), and weight

ratio of total fiber content (TFC) on tensile

properties and dimensional stability of

wood-plastic laminates.

Experiment Design

CRD design with factorial treatment

3 levels of plastic layer (1, 2, and 3 ply)

3 levels of fiber content (50, 50, and 70%)

Each treatment had 3 reps

27 total samples

Materials

SYP Kraft obtained from a local paper mill

(avg. fiber length of 3.0 mm and aspect

ration of 58.2)

Polypropylene films (0.75 mil)

Handsheet Preparation

500 g of pulp added to 1 gal. water > slurry

Excess water removed with a deckle box.

Mat had a water to OD pulp ratio of 4:1

Wood Fiber-PP Laminate

Assemblies (5in. x 5in.) were hot pressed at

400◦ F.

10 min. total press time

Pressed to 1/8 in. stops in 15 sec.

Testing

• Dimensional Stability: 2 hr. boil

• Handsheet porsity: image analysis

• Tensile strength (ASTM D 638): MORt, MOEt

ELONG - % of elongation at break,

• SEM – fracture surface of tensile samples

EFFECT OF LAYER ON MOR OF

WOOD FIBER-PP LAMINATES

4000

5000

6000

7000

8000

1 2 3

Number of PP Films Between Two Handsheets

Ten

sil

e M

OR

(p

si)

A AB B

EFFECT OF FIBER CONTENT ON MOR

5500

5700

5900

6100

6300

6500

50 60 70

Fiber Content (%)

Ten

sil

e M

OR

(p

si)

B

AA

INTERACTION OF LAYER AND FIBER

CONTENT ON MOE

100

150

200

250

300

1 2 3

50

60

70

Number of PP Films Between Two Handsheets

Ten

sil

e M

OE

(1

03

psi)

EFFECT OF FIBER CONTENT ON

DIMENSIONAL STABILITY

EFFECT OF PLASTIC LATER ON

DIMENSIONAL STABILITY

1 layer

2 layers

3 layers

More layers

allows the

plastic to

better melt

and flow into

the voids.

HANDSHEET

POROSITY

SEM Micrograph of Tensile

Fracture for Fiber-PP Laminate

Note: fiber breakage,

not pulled out

SEM Micrograph of Inner Surface

NOMFC = 50, LAYER =1

Interpenetration of

PP films to fiber

network, mechanical

anchor

SEM Micrograph of Outer Surface

NOMFC = 50, LAYER =1

Thin handsheets

allowed PP to

migrate to the

outer surface

SEM Micrograph of Inner Surface

NOMFC = 70, LAYER =3

Less interpenetration,

less plastic, thicker

handsheets

SEM Micrograph of Outer Surface

NOMFC = 70, LAYER =3

Less PP on the surface

Conclusions (1)Experimental results show that laminates of

LAYER 1 had better MORt than those of LAYER 3,

due to better interpenetration of plastic, as

evidenced in SEM observation.

With proper control of LAYER, wood fiber-

polypropylene laminates with fiber loading as high

as 70% could be fabricated with favorable

mechanical properties.

Conclusions (2)

Dimensional stability of wood fiber-polypropylene

laminates were appreciably affected by both NOMFC and

LAYER. An increase in NOMFC and LAYER led to an

increase in WA, LE and TS.

Without surface treatment, lower NOMFC and LAYER

showed best dimensional stability.

Conclusions (3)SEM micrographs showed that the major failure mode of

wood fiber-polypropylene laminates was fiber breakage.

Voids existed inside and on the surface of the laminates;

therefore, precautions should be taken to avoid the

enclosure of air bubbles and the excess shrinkage of PP

in order to improve the strength properties.

tshupe@agcenter.lsu.edu

(225) 578-6432