Biocomposites & Additive Manufacturing

Silane Surface Treatment in Ragweed-Reinforced PLA Biocomposites

Developing sustainable composite filament from an invasive weed: fiber extraction, AMEO and GLYMO silane treatment, twin-screw extrusion, FDM printing, and a full mechanical, thermal and morphological characterization campaign.

By Musa Ibne Mannan · Erik Jonsson School of Engineering and Computer Science, The University of Texas at Dallas

Why ragweed

Natural fiber composites promise a lower-impact alternative to glass reinforcement, but the fiber source usually competes with food or land use. Giant Ragweed does neither — it is an aggressive invasive weed with no commercial demand. If its fiber can reinforce a biodegradable matrix, the material is sustainable at both ends of its life.

The obstacle is chemical. Natural cellulose fibers are strongly hydrophilic; PLA is hydrophobic. Left untreated they do not bond well, the interface fails under load, and the composite underperforms the neat polymer it was supposed to improve. This project examined whether silane surface treatment could bridge that mismatch, and which silane does it better.

From weed to filament

1. Fiber preparation. Giant Ragweed was harvested and processed by chemical retting in 30 percent hydrogen peroxide followed by mechanical rolling to liberate the fibers, which were then ground to powder.
2. Surface treatment. Fibers were treated with GLYMO (3-glycidyloxypropyltrimethoxysilane) in an isopropyl alcohol solution, and separately with AMEO, to reduce the hydrophilic character of the fiber surface and improve adhesion to the PLA matrix.
3. Extrusion. Treated fiber powder was compounded with PLA pellets on a Thermo Scientific Process 11 twin-screw extruder to produce composite filament.
4. Printing. Tensile and flexural test coupons were fabricated by fused deposition modelling, which required parameter optimization to prevent nozzle clogging from the fiber loading.

Did the treatment work?

Energy dispersive X-ray spectroscopy confirmed the presence of silicon on the ragweed fiber surface for both AMEO and GLYMO, validating that the silane chemistry had actually modified the fiber rather than simply washing off. SEM imaging then showed proper fiber–matrix adhesion with no detachment between PLA and ragweed, and cross-sections revealed dense internal packing and homogeneity without noticeable voids or fiber pull-out. Filament surfaces were smooth and continuous, indicating good melt flow and uniform fiber incorporation through the extruder.

Mechanical results

The two silanes split the result rather than one winning outright. GLYMO gave markedly better flexural strength — 54.24 MPa against 42.70 MPa — which points to better interfacial adhesion and reduced internal crack propagation. AMEO produced the higher flexural modulus at 2.431 GPa against 1.82 GPa, indicating a stiffer but less crack-tolerant interface. Which is preferable depends entirely on whether the application is strength-limited or stiffness-limited.

Tensile performance was the weak point. Ultimate tensile strength for GLYMO-treated samples averaged 19.65 MPa, which I would call mediocre, and elongation of 1.88 percent confirms a brittle composite. I attribute this primarily to two causes rather than to the chemistry: fiber size was inconsistent, with length-to-width ratios ranging from 2:1 to 8:1, and the printed specimen design allowed cracks to initiate near the grips. Both are process problems with clear remedies.

A parallel study using maleic anhydride treatment on the same fiber system achieved a roughly 21 percent increase in tensile strength and 40 percent increase in modulus over neat PLA, which suggests the ceiling for this material is considerably higher than the silane tensile numbers alone indicate.

Thermal behaviour

Thermogravimetric analysis showed the composite beginning to decompose above 300 °C and fully disintegrating around 492 °C. Differential scanning calorimetry identified a glass transition temperature of 186 °C and a melting point of 361 °C for the composite filament. That window comfortably accommodates FDM processing while leaving useful thermal headroom in service.

What I would change

The characterization was thorough and the interfacial chemistry demonstrably worked. The limiting factor was upstream: fiber size consistency. Screening the ground fiber to a controlled aspect ratio distribution before compounding is the single change most likely to lift the tensile numbers, and specimen geometry should be revised to move failure initiation away from the grips.