Thongwichean T. a, Phalakornkule C. b and Chaikittiratana A. b

Finite Element Analysis for Thermoforming Process of Starch/

Biodegradable Polyester Blend

aRajamangala University of Technology Srivijaya Rattaphum

College bKing Mongkut’s University of Technology North Bangkok

INTRODUCTIONBioplastics is derived from

renewable resources and could be degraded more easily than petroleum-based plastics.

Starch-based bioplastics is one class of bioplastics. which can be further divided into three categories.

1. thermoplastic starch materials; modified starch with

plasticizing additives. 2. blends of starch and

biodegradable plastics.3. plastics whose monomers are

biochemically derived from starch

3. Elastic-plastic material models were used to capture the compressive

behaviour of the material.

The objective of study 1. Develop a simple computational

modelling using finite element techniques in order to predict the mechanical behaviour of a starch/

biodegradable plastic blend. 2. The mechanical behaviour testing

of thin sheet means of compression tests at temperatures ranging from 363 to 393 K and at strain rates of 0.1 and

0.5 s-1.

Experimental WorkMaterialsThe polymer in this study was

tapioca starch-EnpolTM blend, provided by DES Co.Ltd.

(Thailand). EnpolTM is a fully biodegradable aliphatic polyester resin developed by IRe Chemical Ltd. (Seoul, Korea). The ratio of tapioca starch to EnpolTM was

50:50 by weight

Samples preparation

Twin screw extruder.HAAKE Polylab, Rheomex CTW 100P

Thin strips of extruded tapioca starch- EnpolTM blend.

12 mm.

2 mm.

12 mm.

Specimen dimension of 12x12x2 mm

Plot of endothermic melting vs. temperature

Differential Scanning Calorimeter test

Mechanical Testing In order to determine the

mechanical deformation behaviour of the biodegradable material, the uniaxial compression tests were

performed at various temperatures ranging from 363 K to 393 K with strain rates of 0.1

and 0.5 s-1. The compression tests were carried out according to ASTM D695 using an universal

testing machine equipped with a temperature control chamber

Instron model 5567

4 mm.

Compressing plattens

Stack of small thin samples

Compressing load

Compression test arrangement

Plot of compressive engineering stress vs.

engineering strain at different temperatures and strain rates.

0

10

20

30

40

50

60

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

Compression Engineering Strain

Co

mp

res

sio

n E

ng

ine

eri

ng

Str

es

s (

MP

a)

90 องศาเซลเซ�ยส 90 องศาเซลเซ�ยส100 องศาเซลเซ�ยส100 องศาเซลเซ�ยส110 องศาเซลเซ�ยส110 องศาเซลเซ�ยส120 องศาเซลเซ�ยส120 องศาเซลเซ�ยส

έ = 0.1 s-1έ = 0.5 s-1

έ = 0.5 s-1

έ = 0.1 s-1έ = 0.5 s-1έ = 0.1 s-1έ = 0.5 s-1

έ = 0.1 s-1

363 K 0.5 s-1

363 K 0.1 s-1

373 K 0.5 s-1

373 K 0.1 s-1

383 K 0.5 s-1

383 K 0.1 s-1

393 K 0.5 s-1

393 K 0.1 s-1

0

5

10

15

20

25

30

35

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Compression True Strain

Co

mp

ress

ion

Tru

e S

tres

s (M

Pa)

90 องศาเซลเซ�ยส100 องศาเซลเซ�ยส110 องศาเซลเซ�ยส120 องศาเซลเซ�ยส

363 K 0.5 s-1

373 K 0.5 s-1

383 K 0.5 s-1

393 K 0.5 s-1

Plot of compressive true stress vs. true strain at different

temperatures.

Sheet thermofor

ming

Sheet thermoforming test arrangement

Specimen after the sheet thermoforming process

Finite Element SimulationMaterial Model

Since the deformation behavior was found to be temperature

dependence, strain rate insensitive with no strain hardening after yield,

thus it was modeled with a standard isotropic elastic-perfectly plastic material model inbuilt in a

commercial finite element package ABAQUS 6.5 .

Material's Properties for elastic-perfectly plastic material model.

Temperature (K)

Young's

Modulus (MPa)

True Yield stress (MPa)

363 484.387 28.307373 380.168 23.757383 341.897 20.313393 314.767 17.293

0

5

10

15

20

25

30

35

40

45

50

55

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Compression Engineering Strain

Co

mp

ress

ion

En

gin

eeri

ng

Str

es

s (M

Pa)

ทดสอบท�� 90 องศาเซลเซ�ยส ทดสอบท��100 องศาเซลเซ�ยส ทดสอบท��110 องศาเซลเซ�ยส ทดสอบท��120 องศาเซลเซ�ยส

แบบจำ�าลองท�� 90 องศาเซลเซ�ยส แบบจำ�าลองท�� 100 องศาเซลเซ�ยส แบบจำ�าลองท�� 110 องศาเซลเซ�ยส แบบจำ�าลองท�� 120 องศาเซลเซ�ยส

363 K Data

373 K Data

383 K Data

393 K Data

363 K Simulation

373 K Simulation

383 K Simulation

393 K Simulation

Comparison between experimental data and finite

element simulation with elastic-perfectly plastic material model.

A finite element model was developed to simulate the matched

mould thermoforming process at 393 K described in section 2.5 using a finite element package ABAQUS 6.5. The process was

symmetrical and thus one-half of the system was modeled. 2-D shell

elements (S8) were employed incorporating with the isotropic elastic-perfectly plastic material

model.

Finite element simulation of thermoforming process.

Distribution of the specimen's final thickness predicted by

the finite element simulation.

Distribution of Von Mises' stress in the moulded specimen

predicted by the finite element simulation.

0

200

400

600

800

1000

1200

1400

0 2 4 6 8 10 12

Displacement (mm)

Lo

ad

(N

)

การทดลอง แบบจำ�าลองอ�ลาสติ�ก- เพอร�เฟคล�พลาสติ�ก

DataFE Simulation

Comparison between the compressing load measured

during the forming process and the prediction from the

simulation.

Conclusion 1. It was found that

temperature of 393 K and strain rate of 0.5 s-1 gave the most

satisfying condition for the sheet stamping process.

2. It was found that the Elastic–Perfectly Plastic model described reasonably well the

behavior of the material. 3. The 2D Finite element

simulation of a sheet stamping thermoforming process with

Elastic–Plastic material model can give good representation of the real thermoforming process.

END