1. Flexural Strength vs HT TGA of Microconstituents
Figures: (Left) Increases in strength through heat treatment Too high heat results
in reduced strength, due to (right-TGA) the microconstituents contained in wood
and bamboo begin to degrade at 200 °C.
Mackenzie Kirkpatrick, Austin Levy, Dr. Trevor Harding
Cal Poly Materials Engineering - Spring 2015
Why use bamboo?
Bamboo is a sustainable material with capacity to grow at extremely
fast rates and in diverse locations worldwide. Bamboo is used as a
structural material throughout third-world communities in raw whole-
culm structures and as a composite material in first world in flooring,
paneling, cabinetry, manufactured materials, and other high quality
products.
Thermal Properties of Woody Materials
Thermal heat treatment increases strength and stiffness of
hardwoods and softwoods. Similarities between bamboo and wood’s
microconstituent compositions suggests bamboo would have
similarly increased mechanical properties due to heat treatment.
Hypothesis
Experimental
Sample Fabrication
Full bamboo stalks were fabricated with traditional woodworking
tools to flat, rectangular cross-section samples with dimensions
of:
l = 84 mm, w = 18 +/- 1.5 mm, t = 3.5 +/- 0.7 mm.
Out of 250 fabricated samples, 207 samples were selected for
mechanical testing based on ideal dimensions and appearance.
Mechanical Testing - Three-Point Bend Test
As per ASTM D790-03 “Flexural Properties of Unreinforced and
Reinforced Plastics and Electrical Insulating Materials”
150 kN Instron Tensile Tester Parameters
Support span - 70 mm.
Cross-head movement rate - 2 mm/min
Output Values - Stress (MPa) and strain (mm).
From the output values, the maximum flexural strength and
flexural modulus at 1 mm extension were calculated.
Final Testing Layout
There is an optimal combination of heat treatment time
and temperature to significantly increase the flexural
strength and stiffness of bamboo. Heat treatments (HT)
between 130-170°C should be most effective due to
thermal stability and maximum heat flux into bamboo at
this temperature range.
Thermal Analysis
Figures: Whole culm bamboo structures and composite bamboo bicycles
Variance in Bamboo
Bamboo displays a gradient in fiber content from the inside to the
outside of each culm, as well as along each culm length. Fibers
represent the main structural component of bamboo with higher
cellulose content.
Figures: (Left) Example of fiber content ‘down’ and (right) the cross section of a
sample with fiber gradient
Results
Statistically higher mechanical properties for all HT versus no HT.
No statistical difference between various HT, although trends
observed.
Mechanical Testing
Theory of Mechanism
● Mass loss of wood microconstituents at 100°C is mainly
due to moisture content (TGA).
○ Hemicellulose and lignin have more loss→
higher connectivity with water
● Heat treatment increases available bonding sites by
reducing contact with water
● Free sites bond with other microconstituents, increasing
connectivity throughout structure
● Higher connectivity increases strength and stiffness
● Energy absorption (DSC) is greatest at 140°C
○ Greatest increase in strength and stiffness at
that temperature
TGA DSC
Funding for the printing of this poster provided by MATE alumni.
EFFECT OF HEAT TREATMENT ON THE MECHANICAL
PROPERTIES OF NATURAL BAMBOO