Adhikary 7416

Durability of Wood Flour-Recycled Durability of Wood Flour-Recycled Thermoplastics Composites Under Thermoplastics Composites Under

Accelerated Environmental ConditionsAccelerated Environmental Conditions

Kamal Adhikary, Shusheng Pang and Mark Staiger

Department of Chemical and Process Engineering University of Canterbury

Christchurch, New Zealand

Ecocity World Summit 2008, San Francisco, USA22-26 April 2008

Background Objectives Experimental Programs Results and Discussions Conclusions

Presentation outlinePresentation outline

1. Total MSW generation in 2006 in USA was 251 million tons (USEPA 2006). Recycled 82 million tons of MSW (32.5 %).

2. 1.3 billion tonnes of MSW generated in Europe3. Worldwide plastics production: 245 million tonnes (PlasticEurope 2008).

BackgroundBackground

BackgroundBackground

Total MSW generation in 2006 in USA was 251 million tons.

– Plastics comprise 11.7 percent

– Wood follows at 5.5 percent – 9.4% of wood generated was recovered

– 6.9% of plastics waste generated was recovered/ or recycled

Recovery rate of post-consumer end-of-life plastics in Europe was 50% in 2006.

About 35,000 tonnes (13.48% of total imported virgin plastics) was recycled in 2004 in New Zealand

Increased use of recycled plastics and wood waste offers the prospect of lessening waste disposals and reducing the product costs

BackgroundBackground

Recycled plastics and wood waste are,

Lower cost than competitive materials (especially those based on synthetic polymer), For example, HDPE recycled pellet and flake is 31- 34% less expensive than virgin

Renewable resources Additional market for recycled plastics and

wood waste Reduce waste disposal burden Properties are comparable to virgin plastics

Development of new value added wood-plastic composite material utilizing recovered plastics and

wood waste will have a greater importance from both engineering and economic points of view

What is Wood-Plastic Composite?What is Wood-Plastic Composite?

Wood-plastic composite is manufactured by dispersing wood particles into molten plastic with coupling agent/ or additives to form composite material that can be processed

like a conventional plastic and has the best features of wood and plastics

Advantages over its constituent’s materials

Compare to wood it has lower water uptake, thickness swell, and highly durable against bio-deterioration, also reduce the machine wear and tear of processing equipment, and lowers the product cost against inorganic fillers

Compare to polymer it has higher mechanical properties, thermal stability, and more resistant to ultraviolet light and degradation

ObjectivesObjectives

Investigate the performance of wood-plastic composites (WPCs) made of recycled plastics and sawdust

Evaluate dimensional stability, mechanical properties, morphology and thermal properties of WPCs

Examine durability performance for outdoor applications

Experimental: Experimental: MaterialsMaterials

1: Wood filler Pinus radiata sawdustFresh sawdust was dried and

grounded to fine flour (0.18 and 0.5 mm) 0.00

20.00

40.00

60.00

80.00

7 10 18 35 45 80 120 140

Sieve num ber

Per

cen

tag

e re

tain

ed, %

Size distribution of radiata pine flour

Polymer typeMelt flow index, g/10min/(190°C / 2.16

kg)

Virgin HDPE 0.1

Recycled HDPE 0.07

Virgin PP 25

Recycled PP 21

2: Thermoplastic polymer Recycled thermoplastics (HDPE and

PP) collected from Local Plastics Recycling Company.

Virgin HDPE (grade GM4755) and virgin PP (Hyundai Séetec M1600, polypropylene co-polymer)

Coupling agent: Maleated polypropylene (Epolene G-3015)

Experimental: Composite preparationExperimental: Composite preparation

Mixing/compounding of wood flour and plastic: using a

co-rotating twin screw extruder. Composite formulation used:

Wood flour: 0, 30, 40, 50 and 60 wt. % MAPP content: 3-5 wt. %

Pressing mold temperature: 170 C for HDPE series and 190 C for PP series; hot pressed for 5 min under 5 MPa, and then cold pressed under same pressure.

Target panel density: 800-950 kg/m3 Composite panel size: size:

165 mm 152 mm 6.4 mm

Sawdust (wood-flour)

Mixing/Compounding

Recycled Plastics

WPC’s panel (Final product)

Hot/Cold pressing of pelletsWood-plastics Pellets

Wood-plastic composite manufacturing process flow

Composite formulations (% by weight)Composite formulations (% by weight)

Composite sample code

Polymer type

Polymer form

Polymer content (%)

Wood flour (%)

Coupling agent (%)

vPE50W50 HDPE Virgin 50 50 0

rPE50W50 HDPE Recycled 50 50 0

vPP50W50 PP Virgin 50 50 0

rPP50W50 PP Recycled 50 50 0

rPP45W50CA5 PP Recycled 45 50 5

Accelerated weathering testsAccelerated weathering tests1. Accelerated freeze-thaw cycles

Samples exposed to Accelerated Freeze–Thaw Cycles (ASTM D6662–01) for 12 full cycles.

One complete weathering cycle consisted of:(i) Water soaks until no further weigh gain (ii) Freezing for 24 h (Chest freezer at –27°±3°C)(iii) Thawing for 24 h (21°C±3°C and 50±5% RH)

2. Accelerated UV-exposure

Samples exposed to Fluorescent UV light-exposure apparatus (ASTM D4329-99).

Exposure for 2000 h Lamp type: UVA-340Irradiance: 0.77 W/m2 (~ wavelength of 340 nm)

Testing and analysisTesting and analysis

Water absorption & thickness swelling tests (ASTM D570-98). Mechanical properties: Flexural properties (ASTM D790) using

Universal Testing Machine. Morphology of the fracture surface of bending test specimens are

investigated by using high resolution field emission scanning electron microscopy.

Surface color of control and weathered samples are measured using Minolta Spectrophotometer (ASTM D2244).

Thermal properties are measured by using Differential Scanning Calorimetry- Scanned from 50 to 200oC at a heating and cooling rate of 2oC/min.

2 h Water Absorption

0

2

4

6

Wat

er a

bsor

ptio

n (%

)

Control

FT cycled

UV weathered

0

3

6

9

12

Wat

er a

bsor

ptio

n (%

)

Control

FT cycled

UV weathered

Water absorption by WPCs in Water Submersion

ResultsResults

24 h Water Absorption

24 h Thickness Swelling (%)

0

2

3

5

vPP5

0W50

rPP5

0W50

rPP4

5W50

CA5

vHDPE50

W50

rHDPE50

W50

Thi

ckne

ss S

wel

ling

(%)

Control

FT cycled

UV weathered

Results Contd……Results Contd……

Thickness Swelling by WPCs in Water Submersion

Flexural MOR of the WPCs Flexural MOE of the WPCs

0.0

1.0

2.0

3.0

MO

E (

GPa

)

Control

FT cycled

UV weathered

0

15

30

45

MO

R (M

Pa)

Control

FT cycled

UV weathered

Results Contd……Results Contd……

Flexural properties of WPCs

-90

-60

-30

0

30

60

90

vPP50

W50

rPP50

W50

rPP45

W50

CA5

vHDPE50

W50

rHDPE50

W50

% c

hang

e in

val

ues

MOR MOEYield stress Elongation at break

Results Contd……Results Contd……

Changes in flexural properties of WPCs after 12 FT cycles

Results Contd……Results Contd……

Surface colour measurement

ΔE – Discoloration; ΔL*- lightening; Δa*and Δb*-chromaticity coordinates

Δa* Δb* ΔL* ΔE Δa* Δb* ΔL* ΔE

vPP50W50 -2.3 -6.9 6.6 9.8 -3.3 -9.5 7.2 12.3

rPP50W50 0.2 1.2 10.4 10.5 -0.2 0.9 14.0 14.0

rPP45W50CA5 -0.3 -0.2 7.4 7.5 0.0 0.4 5.3 5.3

vHDPE50W50 -0.8 -4.7 -1.4 5.0 -1.1 -3.1 6.1 6.9

rHDPE50W50 0.3 1.8 4.8 5.2 0.1 0.6 2.6 2.7

Composite specimen code

After 12 FT cycles After 2000 h UV weatheing

0

4

8

12

16de

ltaE

Val

ue

500 h 1000 h

1500 h 2000 h

Discoloration values (ΔE) for UV-Weathered PP-wood flour Composites

Results Contd……Results Contd……

Results (contd.)Results (contd.)

SEM images of rPP50W50 (a) control and (b) UV-weathered samples

Microstructural characterization

Results (contd.)Results (contd.)

SEM images of rPP45W50CA5 (a) control (b) FT-weathered samples

Microstructural characterization

Results contd…..Results contd…..

DSC thermograms (2nd heating) for PP based control and FT weathered composites

Thermal properties of WPCs

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

50 80 110 140 170 200

Temperature (oC)

Hea

t flo

w (W

/g)

rPP100

vPP50W50

rPP50W50

FT-vPP50W50

FT-rPP50W50

Crystallization temperature (Tc) and enthalpy (ΔHc) were measured from 1st cooling run Peak melting temperature (Tm) and enthalpy (ΔHm) were measured from 2nd heating cycle Crystallinity (Xc):

ΔHf :Expt. heat of fusion, ΔHf100 is the theoretical heat of fusion for a 100% crystalline thermoplastic (ΔHf100=205 J/g for PP and ΔHf100=293 J/g for HDPE), and w is the mass fraction of thermoplastic in the composite samples

wH

HX

f

fc *

100

Results (contd.)Results (contd.)

Thermal properties

Melting enthalpy and crystallinity of UV-weathered composites was decreased compared to corresponding control samples.

Peak melting temperature and peak crystallization temperature changed slightly.

Wood fibers in composite act as nucleating agent and retards the crystallization rate.

Loss of crystallinity due to weathering degradation resulted the decrease in composite properties.

ConclusionsConclusions

The results of this work so far provided the evidence that the recycled thermoplastics (HDPE and PP) and wood sawdust can be successfully used to produce stable and strong wood plastic composites.

Improved stability can be achieved by increasing the polymer content or by addition of coupling agent.

Properties degradation is observed after Freeze-Thaw and UV weathering.

Property ComparisonProperty Comparison

Property HDPE based WPC

PP based WPC

PP lumber

Pine lumber

Regular MDF

(3mm)

Flexural MOR (MPa)

14.4-25.5 17.4-39.6 28.7 80.0 40.0

Flexural MOE (GPa)

1.06-1.97 1.7-2.5 1.39 7.9 3.0

24 h water absorption (%)

0.98-4.1 1.2-3.7 <0.01 17.2 2-3 (1h)

24 h thickness Swelling (%)

0.42-2.5 0.8-1.5 - 2.6 1.7-3.8 (1h)

Potential ApplicationsPotential Applications

Low Stress Applications:

Residential/Commercial decking products

Boardwalks and DocksWindows and door partsSiding and accessoriesFencingOthers: Roofing, Outdoor furniture,

Landscape timbers, Playground equipment

Exterior building trim Industrial flooring

AcknowledgementsAcknowledgements

Mr Jeremy Warnes and Mr Ross Anderson of Scion on extrusion experiments

Mr Murray Taylor and Mr Henry Baker of AgResearch (Lincoln) on hot press experiments

New Zealand Plastics Recycling Ltd. to supply the recycled plastics

Technicians from Departments of Mechanical Engineering, and Chemical and Process Engineering

New Zealand Development Scholarships (NZDS) scheme of NZAID

Funding from New Zealand Foundation for Research, Science and Technology

Thank you.Thank you.

Any questions, comments, suggestions??

Additives (Contd…)Additives (Contd…)

Modification scheme for esterification reaction between wood particles and maleated polyolefins: (a) monoester and (b) diester formation.