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 HardingCal 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 FabricationFull 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 TestAs per ASTM D790-03 “Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials”

150 kN Instron Tensile Tester ParametersSupport span - 70 mm. Cross-head movement rate - 2 mm/minOutput 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