# Natural Fibre Composites Research

> A controlled comparison of vacuum-infused flax and hemp epoxy laminates at MIT Manipal, covering mechanical, thermal, fire and acoustic properties. Published in two journal papers with Sohan Kumar Y.

- Role: Researcher and co-author
- Year: 2026
- Page: https://madhavsonkusare.com/work/natural-fibre-composites/

## Achievements

- 2 papers in Sci (MDPI), 2026
- First author · thermal and acoustic paper
- Flax vs hemp · vacuum infusion

## The question

We compared two natural-fibre epoxy laminates using the same treatment, resin, fibre orientation and manufacturing process.

## Making the laminates

Alkali-treated flax and hemp fabrics were vacuum-infused with the same epoxy system. Five unidirectional plies were cured under vacuum at room temperature.

- Figure: Fibres before treatment (left) and after 30 minutes in 5 wt.% NaOH (right)
- Figure: Vacuum infusion set-up: resin inlet, fibre stack under the bag, outlet, catch-can, pump

## Mechanical tests

Five specimens per test. Published means ± standard deviations: flexural strength 116 ± 3 MPa (flax) and 102 ± 4 MPa (hemp); flexural modulus 5.9 ± 0.1 and 4.9 ± 0.1 GPa.

Notched Charpy impact: 5.7 ± 0.3 and 10.6 ± 0.8 kJ/m². Interlaminar shear strength: 12.9 ± 0.6 and 14.3 ± 0.3 MPa, for flax and hemp respectively. Both showed brittle failure in tension, bending and shear.

- Figure: Flexural strength (left) and impact strength (right), flax and hemp, five specimens each
- Figure: SEM fracture surfaces: flax (left) with clean pulled-out fibres, hemp (right) resin-coated

## Heat, fire, sound

At 5% mass loss in nitrogen, temperatures were 207 ± 3 °C for flax and 222 ± 3 °C for hemp. Glass transition on second heating was 65.3 ± 0.5 and 71.9 ± 0.9 °C; the paper attributes the difference to cure state. Mass-loss temperatures are not service-temperature ratings.

Both laminates had an oxygen index of 21.54 vol.% and UL 94 HB classification. Horizontal burning rates were 26.58 ± 0.68 mm/min for flax and 24.31 ± 0.68 mm/min for hemp.

Normal-incidence transmission loss averaged 11.56 dB for flax and 13.22 dB for hemp at 250, 500, 1000 and 2000 Hz. Relative performance varied with frequency.

- Figure: Mass loss (left) and rate of mass loss (right) in nitrogen, 30 to 800 °C at 10 °C/min
- Figure: Normal-incidence transmission loss, 63 to 6300 Hz, flax and hemp laminates

## What it means

Under the tested conditions, flax had higher flexural values; hemp had higher impact and interlaminar shear values. Thermal and acoustic responses also differed, while both shared the same HB fire classification.

Fibre volume fraction was not measured in the mechanical study. These tests do not establish fatigue, ageing or in-service performance.

## Gallery

- Circular specimen cut by water jet for the impedance tube
- Impedance tube set-up used for the transmission loss tests
- Universal testing machine, 50 kN load cell, used for the tensile tests
- Brittle failure of a flax/epoxy tensile specimen

## Published papers

- [Thermal and acoustic properties of flax and hemp epoxy bio-composites](https://doi.org/10.3390/sci8090261) (Sci · 17 Sep 2026 · first author)
- [Mechanical performance of alkali-treated flax and hemp epoxy composites](https://doi.org/10.3390/sci8060133) (Sci · 9 Jun 2026 · second author)

## Links

- [Thermal and Acoustic Properties of Flax and Hemp Epoxy Bio-Composites Fabricated Using Vacuum-Assisted Resin Infusion Moulding](https://doi.org/10.3390/sci8090261) (Sci · 17 Sep 2026 · first author)
- [Comparative Mechanical Performance of Alkali-Treated Unidirectional Flax/Epoxy and Hemp/Epoxy Composite Manufactured via VARIM](https://doi.org/10.3390/sci8060133) (Sci · 9 Jun 2026 · second author)
- [Publication list](https://sciprofiles.com/profile/madhav_sonkusare/publications) (SciProfiles)