Fully Bio-Based Composites Based on PHA and Cellulose Filaments: Investigating the Impact of Fiber Modification on Composite Properties

Fully bio-based vapor barrier membranes were developed for use in building envelopes. These membranes, positioned within interior walls, are designed to control moisture migration and prevent the accumulation of humidity that can compromise building materials. The membranes were fabricated from polyhydroxyalkanoate (PHA) incorporated with various concentrations (1–20 wt%) of cellulose filaments (CFs). To enhance compatibility with the PHA matrix, the CFs were modified using a commercial ester-based surfactant. Fourier-transform infrared spectroscopy (FT-IR) confirmed improved chemical interactions between the modified CFs and the PHA matrix. Differential scanning calorimetry (DSC) revealed that the modified CFs acted as nucleation sites, introducing a new crystallization peak around 76–88 °C and shifting existing peaks to higher temperatures as CF content increased, indicating enhanced crystal nucleation and lamellar growth. Water vapor barrier transmission test demonstrated that PHA composites with modified CFs exhibited superior barrier properties compared to those with untreated CFs. For instance, composites containing 10 wt% modified CFs showed dramatically improved performance, with normalized water vapor transmission rate (N-WVTR) values reduced by 454% (method A) and 393% (method B) relative to composites with 10 wt% untreated CFs. Biodegradability testing with Aspergillus niger and Penicillium chrysogenum confirmed the environmental compatibility of the composites, with mass losses up to 5% over the testing period. These results suggest that the developed PHA-based membranes offer a promising, sustainable alternative to conventional petroleum-derived vapor barriers in building envelope applications.