{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,26]],"date-time":"2026-02-26T12:11:43Z","timestamp":1772107903020,"version":"3.50.1"},"reference-count":69,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2026,2,26]],"date-time":"2026-02-26T00:00:00Z","timestamp":1772064000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Latvian Council of Science State Research Program: \u201cInnovation in Forest Management and Value Chain for Latvia\u2019s Growth: New Forest Services, Products and Technologies\u201d","award":["VPP-ZM-VRIIILA-2024\/2-0002"],"award-info":[{"award-number":["VPP-ZM-VRIIILA-2024\/2-0002"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>To improve the extrusion processing of wood\u2013plastic composites (WPCs), functional additives known as internal lubricants are incorporated into the composite formulations. The lubricants play a crucial role in decreasing the melt viscosity of WPCs, which in turn has a positive impact on energy consumption, productivity, and overall composite performance. This study shows the effect of suberinic acids (SAs), extracted from birch outer bark via alkaline water and water\u2013ethanol hydrolysis at different pH values, on the processing behavior and properties of a recycled polypropylene-based composite filled with pine microfibers. The extracted SAs were characterized by gas chromatography\u2013mass spectrometry, Fourier transform infrared spectroscopy, gel permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry. The conducted analyses revealed notable differences in the chemical composition, molecular weight, and molecular polydispersity of the SAs. Betulin was identified as the dominant component (49\u201386%). The pine sawdust was treated with 2% NaOH at 90 \u00b0C for 90 min prior to composite fabrication. The incorporation of 4.0 wt% SAs into the WPC formulations reduced the extruder rotor\u2019s maximum and minimum torques torque, indicating improved processability of the composite. Mechanical and wetting properties of the WPC samples were evaluated. The samples containing SAs exhibited an increased elongation at break by 37.9\u201351.6% and bending deformation by 12.8\u201317.5%, depending on the extraction conditions of SAs, accompanied by a slight reduction in the mechanical properties and slight increase in water sorption compared with the composite filled with the alkaline-treated pine microfibers. The results showed enhanced flexibility and ductility in the SAs-containing WPCs. The presence of a 1.0 wt% maleic anhydride-grafted polypropylene in the samples led to an increase their mechanical properties, along with the reduced water sorption.<\/jats:p>","DOI":"10.3390\/polym18050564","type":"journal-article","created":{"date-parts":[[2026,2,26]],"date-time":"2026-02-26T11:23:45Z","timestamp":1772105025000},"page":"564","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Fabrication and Properties of Pine Fiber-Reinforced Polymer Composite Incorporating Suberinic Acids Extracted Under Different Conditions"],"prefix":"10.3390","volume":"18","author":[{"given":"Anrijs","family":"Verovkins","sequence":"first","affiliation":[{"name":"Latvian State Institute of Wood Chemistry, Dzerbenes 27, LV-1006 Riga, Latvia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Galia","family":"Shulga","sequence":"additional","affiliation":[{"name":"Latvian State Institute of Wood Chemistry, Dzerbenes 27, LV-1006 Riga, Latvia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4825-3053","authenticated-orcid":false,"given":"Janis","family":"Rizikovs","sequence":"additional","affiliation":[{"name":"Latvian State Institute of Wood Chemistry, Dzerbenes 27, LV-1006 Riga, Latvia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Brigita","family":"Neiberte","sequence":"additional","affiliation":[{"name":"Latvian State Institute of Wood Chemistry, Dzerbenes 27, LV-1006 Riga, Latvia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Daniela","family":"Godina","sequence":"additional","affiliation":[{"name":"Latvian State Institute of Wood Chemistry, Dzerbenes 27, LV-1006 Riga, Latvia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4640-5121","authenticated-orcid":false,"given":"Laima","family":"Vevere","sequence":"additional","affiliation":[{"name":"Latvian State Institute of Wood Chemistry, Dzerbenes 27, LV-1006 Riga, Latvia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0006-0410-5178","authenticated-orcid":false,"given":"Rudolfs","family":"Berzins","sequence":"additional","affiliation":[{"name":"Latvian State Institute of Wood Chemistry, Dzerbenes 27, LV-1006 Riga, Latvia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Talrits","family":"Betkers","sequence":"additional","affiliation":[{"name":"Latvian State Institute of Wood Chemistry, Dzerbenes 27, LV-1006 Riga, Latvia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Valerija","family":"Kudrjavceva","sequence":"additional","affiliation":[{"name":"Latvian State Institute of Wood Chemistry, Dzerbenes 27, LV-1006 Riga, Latvia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,2,26]]},"reference":[{"key":"ref_1","unstructured":"(2026, February 20). 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