ei265 3-Point Flexural Test of Cellulose Nanofibers Reinforced

Application

News

No.

i265

Material Testing Machine

3-Point Flexural Test of Cellulose Nanofibers

Reinforced Plastics

LAAN-A-AG-E025



Introduction

Plastic foam is lightweight and has excellent thermal

insulating and shock-absorbing properties because the

interior of the material contains numerous voids. On the

other hand, the strength of plastic foam is lower than that

of non-foam materials, as the volume of plastics per unit

volume is smaller. Addition of fiber or other reinforcing

materials is one technique for obtaining satisfactory

strength in materials in which foaming is used to impart

light weight and thermal insulating properties. Although

glass fiber and carbon fiber are often used as reinforcing

materials, research and development using cellulose

nanofibers (hereinafter, CNF) as a plant-derived high

performance new material has progressed recently.

Cellulose, consisting mainly of substances such as plant

cell walls and cotton, is the most common

carbohydrate on Earth and has long been used as a raw

material for paper and cotton fiber. Recently, CNF with

higher functionality realized by defibrating cellulose to

the nano level has attracted interest. As a plant-derived

material, CNF has a low environmental impact, and also

has a variety of desirable properties, including low

linear expansion, a gas barrier property, and

transparency. In comparison with ferrous materials,

CNF weighs only 1/5 as much but has a high specific

strength, being 5 times stronger than steel, and

strength equal or superior to that of the conventional

materials can be realized compounding CNF with

plastics and rubber. Therefore, CNF has attracted

interest as a new material following carbon fiber.

This article introduces a 3-point flexural test using a

deflection measuring device and test speed in

compliance with JIS K 7171, which is generally used in

strength evaluation of plastics, and compares the

differences in flexural strength with/without CNF and

with/without foaming.

Y. Kamei



Specimens

The CNF reinforced plastic measured in the study was a

high density polyethylene (hereinafter, HDPE). Test

specimens

were prepared by adding 5 % CNF to

HDPE as the matrix plastic. To investigate differences in

the internal condition, internal observation of the

specimens was performed with an inspeXio SMX-

100CT microfocus X-ray CT system prior to the tests.

Fig.

1 shows CT images of the specimens, in which

voids appear as black areas. There is no large difference

between the non-foamed plastic without CNF ( ) and

the non-foamed CNF reinforced plastic ( ). In the

foamed plastics, it was found that finer voids existed in

a uniformly dispersed condition in the CNF reinforced

plastic ( ) than in the plastic without CNF. Thus, the

possibility that CNF impedes the growth and

coalescence of voids is conceivable.

*1 Specimens provided by Kyoto Municipal Institute of Industrial

Technology and Culture, a Local Incorporated Administrative

Agency.



Measuring System

Fig. 2 shows the condition of the test, and Table 1

shows the test conditions. After measuring flexural

modulus of elasticity, the test speed was changed in

order to measure flexural strength efficiently. For

precise measurement of the deflection of the

specimens, the test was performed by using a

deflectometer in the displacement measurements.

Fig. 1 CT Images

Fig. 2 Condition of Test

Table 1 Test Conditions

Instrument AGS-X

Load Cell 1 kN

est Fixture Three-Point Bending Test Jig for

Plastic

(Punch R5, Supports R5)

Distance Between Supports 40 mm

Flexural Deflection

Measurin

Devices

Deflection Measuring Device for

Three-Point Bendin

Test

Software TRAPEZIUM X Sin

est Speed 1 mm/min → 20 mm/min

Number of Tests 3 Pieces/Specimen

Specimen Dimensions 50 mm × 10 mm × 4 mm

HDPE

HDPE (Foam) HDPE + CNF5 % (Foam)

HDPE + CNF5 %

Application

News

No.

i265

First Edition: Feb. 2019

For

Research Use Only. Not for use in diagnostic procedures.

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

Test Results

Fig. 3 shows the test results. With the CNF reinforced

plastics (, ), brittle facture occurred, as can be seen

by the sharp decrease in test force after achieving

maximum strength. The non-CNF plastics ( ,

)

displayed duc

tile behavior, in which the test force

decreased gradually.

Table 2 summarizes the test results for all specimens.

The flexural modulus of elasticity was calculated from

the slope of flexural strain of 0.05 % to 0.25

Comparing th

e values of the non-CNF HDPE ( ,

)

and the

CNF reinforced plastic ( , ), the CNF

reinforced plastic showed higher values for both the

flexural modulus of elasticity and flexural strength.

Moreover, comparing the coefficients of variation of

the flexural strengths of the HDPE plastic foam () and

the CNF reinforced plastic foam (), it was

found that

variation of the CNF rei

nforced plastic was smaller.

Fig. 3 Test Results

Table 2 Summary of Test Results (Average of n=3)

Flexural

Modulus of

Elasticity

(GPa)

Flexural

Strength

(MPa)

Coefficient

of Variation

of Flexural

Strength

(%)

HDPE 1.29 55.2 0.7

HDPE + CNF5 % 1.56 61.8 0.2

HDPE (Foam) 0.87 32.7 4.0

HDPE + CNF 5 % (Foam) 1.29 42.5 0.2



Conclusion

It was possible to increase the flexural modulus of

elasticity and flexural strength of plastic by adding CNF.

In addition to improving those properties, in the case

of plastic foam, it was also found that stable plastic

foam molding, for example, without variations in void

size, is possible by adding CNF.

Although various types of evaluation are necessary for

application of CNF composite materials to members,

evaluation of strength is one key item. In this study, the

deflection of the specimens could be measured with

high accuracy because a deflectometer was used.

Accurate evaluation of the mechanical properties of

materials containing CNF is possible by using

Shimadzu measuring systems.

HDPE

HDPE + CNF5 %

HDPE (Foam)

HDPE + CNF5 % (Foam)

Flexural Strain (%)

Flexural Stress (MPa)

0 3 6 9 12 15 18 21 24