{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,13]],"date-time":"2026-10-13T14:10:54Z","timestamp":1791900654976,"version":"4.3.4"},"reference-count":49,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2022,6,3]],"date-time":"2022-06-03T00:00:00Z","timestamp":1654214400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"European Regional Development Fund, ASTRA \u201cTUT Institutional Development Programme for 2016\u20132022\u201d Graduate school of Functional Materials and Technologies","award":["2014\u20132020.4.01.16-0032"],"award-info":[{"award-number":["2014\u20132020.4.01.16-0032"]}]},{"name":"European Regional Development Fund, ASTRA \u201cTUT Institutional Development Programme for 2016\u20132022\u201d Graduate school of Functional Materials and Technologies","award":["PRG1023"],"award-info":[{"award-number":["PRG1023"]}]},{"name":"Estonian Research Council","award":["2014\u20132020.4.01.16-0032"],"award-info":[{"award-number":["2014\u20132020.4.01.16-0032"]}]},{"name":"Estonian Research Council","award":["PRG1023"],"award-info":[{"award-number":["PRG1023"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>This research investigates an effective alkali (NaOH) treatment and fire-retardant coating to produce biocomposites from frost-retted hemp fiber and PLA. The fiber surface treatment with various NaOH concentrations was investigated throughout a range of soaking times. The results show that the extracted non-cellulosic fiber content increases with treatment duration and NaOH concentration, while the fraction of targeted components removed remains nearly unchanged after soaking for 1, 2, and 4 h with a 5 wt.% NaOH solution. At the composite level, the treatment with 5 wt.% NaOH solution for 1 h emerged as the most efficient, with tensile strength, Young\u2019s modulus, flexural strength, and flexural modulus of 89.6 MPa, 9.1 GPa, 121.6 MPa, and 9.6 GPa, respectively, using 30 wt.% fibrous reinforcement. The fire performance of the examined batches of biocomposites improved significantly with the novel fire-retardant (Palonot F1) coating. However, the tensile strength notably decreased, while the flexural properties showed only a slight reduction. In most cases, the biocomposites with the alkali-treated hemp fiber had delayed ignition during the 5 min exposure to the cone heater. The findings in this work contribute to studies that will be required to give design guidelines for sustainable building options.<\/jats:p>","DOI":"10.3390\/polym14112280","type":"journal-article","created":{"date-parts":[[2022,6,3]],"date-time":"2022-06-03T10:33:01Z","timestamp":1654252381000},"page":"2280","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":20,"title":["Investigation of Efficient Alkali Treatment and the Effect of Flame Retardant on the Mechanical and Fire Performance of Frost-Retted Hemp Fiber Reinforced PLA"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9720-7037","authenticated-orcid":false,"given":"Percy Festus","family":"Alao","sequence":"first","affiliation":[{"name":"Department of Material and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Raimond","family":"Press","sequence":"additional","affiliation":[{"name":"Department of Material and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0082-6983","authenticated-orcid":false,"given":"Heikko","family":"Kallakas","sequence":"additional","affiliation":[{"name":"Department of Material and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jussi","family":"Ruponen","sequence":"additional","affiliation":[{"name":"Department of Biosystems and Bioproducts, Aalto University, Otakaari 1B, 11000 Aalto, Finland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Triinu","family":"Poltim\u00e4e","sequence":"additional","affiliation":[{"name":"Department of Material and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0024-3451","authenticated-orcid":false,"given":"Jaan","family":"Kers","sequence":"additional","affiliation":[{"name":"Department of Material and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,6,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"10768","DOI":"10.1016\/j.jmrt.2020.07.084","article-title":"Effect of hemp fiber length on the mechanical and thermal properties of polypropylene\/SEBS\/hemp fiber composites","volume":"9","author":"Panaitescu","year":"2020","journal-title":"J. Mater. Res. Technol."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"113780","DOI":"10.1016\/j.indcrop.2021.113780","article-title":"From Wood and Hemp Biomass Wastes to Sustainable Nanocellulose Foams","volume":"170","author":"Beluns","year":"2021","journal-title":"Ind. Crop. Prod."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"260","DOI":"10.1016\/j.indcrop.2019.05.040","article-title":"Manufacturing and characterization of sustainable hybrid composites using sisal and hemp fibres as reinforcement of poly (lactic acid) via injection moulding","volume":"137","author":"Pappu","year":"2019","journal-title":"Ind. Crop. Prod."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1632","DOI":"10.1016\/j.compositesa.2008.07.007","article-title":"Characterization of natural fiber surfaces and natural fiber composites","volume":"39","author":"Sgriccia","year":"2008","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"113337","DOI":"10.1016\/j.indcrop.2021.113337","article-title":"Exploring the dew retting feasibility of hemp in very contrasting European environments: Influence on the tensile mechanical properties of fibres and composites","volume":"164","author":"Mazian","year":"2021","journal-title":"Ind. Crop. Prod."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Bhattacharyya, D., Subasinghe, A., and Kim, N.K. (2015). Natural Fibers: Their Composites and Flammability Characterizations, William Andrew Publishing.","DOI":"10.1016\/B978-0-323-26434-1.00004-0"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"286","DOI":"10.1016\/j.compositesb.2014.10.010","article-title":"Influence of compatibilizing system on morphology, thermal and mechanical properties of high flow polypropylene reinforced with short hemp fibers","volume":"69","author":"Panaitescu","year":"2015","journal-title":"Compos. Part B Eng."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Manaia, J.P., Manaia, A.T., and Rodriges, L. (2019). Industrial Hemp Fibers: An Overview. Fibers, 7.","DOI":"10.3390\/fib7120106"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"422","DOI":"10.1016\/j.indcrop.2017.10.049","article-title":"Modification of hemp fibers (Cannabis sativa L.) for composite applications","volume":"111","author":"Batello","year":"2018","journal-title":"Ind. Crop. Prod."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Mohd Ishak, Z.A., and Mat Taib, R. (2015). Multifunctional Polymer Composites Using Natural Fiber Reinforcements, William Andrew Publishing.","DOI":"10.1016\/B978-0-323-26434-1.00003-9"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Marrot, L., Alao, P.F., Mikli, V., and Kers, J. (2021). Properties of Frost-Retted Hemp Fibers for the Reinforcement of Composites. J. Nat. Fibers, 1\u201312.","DOI":"10.1080\/15440478.2021.1904474"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1443","DOI":"10.1007\/BF01111964","article-title":"Alkali treatment of coir fibres for coir-polyester composites","volume":"18","author":"Prasad","year":"1983","journal-title":"J. Mater. Sci."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1219","DOI":"10.1016\/j.cjche.2018.01.008","article-title":"Morphological, mechanical and thermal properties of cyanate ester\/benzoxazine resin composites reinforced by silane treated natural hemp fibers","volume":"26","author":"Zegaoui","year":"2018","journal-title":"Chin. J. Chem. Eng."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"210","DOI":"10.1016\/j.compositesb.2017.09.030","article-title":"Influence of chemical treatments on mechanical properties of hemp fiber reinforced composites","volume":"133","author":"Sepe","year":"2018","journal-title":"Compos. Part B Eng."},{"key":"ref_15","first-page":"1517","article-title":"Effect of Hemp Fibre Length on the Properties of Polypropylene Composites","volume":"17","author":"Alao","year":"2019","journal-title":"Agron. Res."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"2457","DOI":"10.1016\/j.ijbiomac.2020.09.159","article-title":"Characterization on chemical and mechanical properties of silane treated fish tail palm fibres","volume":"163","author":"Sabarinathan","year":"2020","journal-title":"Int. J. Biol. Macromol."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Alao, P., Marrot, L., Burnard, M., Lavri\u010d, G., Saarna, M., and Kers, J. (2021). Impact of Alkali and Silane Treatment on Hemp\/PLA Composites\u2019 Performance: From Micro to Macro Scale. Polymers, 13.","DOI":"10.3390\/polym13060851"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Alao, P., Marrot, L., Kallakas, H., Just, A., Poltim\u00e4e, T., and Kers, J. (2021). Effect of Hemp Fiber Surface Treatment on the Moisture\/Water Resistance and Reaction to Fire of Reinforced PLA Composites. Materials, 14.","DOI":"10.3390\/ma14154332"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"447","DOI":"10.1016\/j.compositesa.2005.05.036","article-title":"The effect of fiber surface treatments on the tensile and water sorption properties of polypropylene\u2013luffa fiber composites","volume":"37","author":"Demir","year":"2006","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"424","DOI":"10.1016\/j.compscitech.2007.06.022","article-title":"Effect of fiber surface-treatments on the properties of laminated biocomposites from poly(lactic acid) (PLA) and kenaf fibers","volume":"68","author":"Huda","year":"2008","journal-title":"Compos. Sci. Technol."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"7152","DOI":"10.1016\/j.biortech.2007.12.073","article-title":"The effects of hemicelluloses and lignin removal on water uptake behavior of hemp fibers","volume":"99","author":"Pejic","year":"2008","journal-title":"Bioresour. Technol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1777","DOI":"10.1016\/j.compositesa.2009.08.013","article-title":"Effect of fiber surface modification on the mechanical and water absorption characteristics of sisal\/polyester composites fabricated by resin transfer molding","volume":"40","author":"Sreekumar","year":"2009","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"14","DOI":"10.1016\/j.compositesb.2014.08.025","article-title":"The effect of alkaline treatment on mechanical properties of kenaf fibers and their epoxy composites","volume":"68","author":"Fiore","year":"2015","journal-title":"Compos. Part B Eng."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"550","DOI":"10.1016\/j.csite.2017.10.012","article-title":"Effect of surface modification on morphological, mechanical and thermal conductivity of hemp fiber: Characterization of the interface of hemp \u2013Polyurethane composite","volume":"10","author":"Sair","year":"2017","journal-title":"Case Stud. Therm. Eng."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"660","DOI":"10.1016\/j.indcrop.2017.07.027","article-title":"Targeted pre-treatment of hemp bast fibres for optimal performance in biocomposite materials: A review","volume":"108","author":"Liu","year":"2017","journal-title":"Ind. Crop. Prod."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"270","DOI":"10.1016\/j.matchemphys.2018.06.040","article-title":"The influence of different chemical treatments on the hemp fiber\/polybenzoxazine based green composites: Mechanical, thermal and water absorption properties","volume":"217","author":"Dayo","year":"2018","journal-title":"Mater. Chem. Phys."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"546","DOI":"10.1016\/j.compositesb.2013.12.014","article-title":"Fire resistance characterisation of hemp fibre reinforced polyester composites for use in the construction industry","volume":"60","author":"Naughton","year":"2014","journal-title":"Compos. Part B Eng."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"251","DOI":"10.1007\/s10443-007-9044-0","article-title":"Fire Retardancy of Natural Fibre Reinforced Sheet Moulding Compound","volume":"14","author":"Hapuarachchi","year":"2007","journal-title":"Appl. Compos. Mater."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"637","DOI":"10.1016\/j.ijbiomac.2019.08.166","article-title":"Investigation into mechanical, absorption and swelling behaviour of hemp\/sisal fibre reinforced bioepoxy hybrid composites: Effects of stacking sequences","volume":"140","author":"Thiagamani","year":"2019","journal-title":"Int. J. Biol. Macromol."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"012019","DOI":"10.1088\/1755-1315\/290\/1\/012019","article-title":"Fire and Mechanical Properties of Hemp and Clay Boards for Timber Structures","volume":"290","author":"Kallakas","year":"2019","journal-title":"IOP Conf. Series Earth Environ. Sci."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"2535","DOI":"10.1016\/j.compscitech.2006.12.012","article-title":"Structure and thermal properties of poly(lactic acid)\/cellulose whiskers nanocomposite materials","volume":"67","author":"Petersson","year":"2007","journal-title":"Compos. Sci. Technol."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1317","DOI":"10.1016\/S0266-3538(03)00103-9","article-title":"Natural fibres as reinforcement in polylactic acid (PLA) composites","volume":"63","author":"Oksman","year":"2003","journal-title":"Compos. Sci. Technol."},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Brounstein, Z., Yeager, C.M., and Labouriau, A. (2021). Development of Antimicrobial PLA Composites for Fused Filament Fabrication. Polymers, 13.","DOI":"10.3390\/polym13040580"},{"key":"ref_34","first-page":"2","article-title":"Ionic Liquid (ILS) Based Fire Retardant for Wood-Based Panels","volume":"2021","author":"Ruponen","year":"2021","journal-title":"World Conf. Timber Eng."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"107062","DOI":"10.1016\/j.compositesb.2019.107062","article-title":"High flow polypropylene\/SEBS composites reinforced with differently treated hemp fibers for injection molded parts","volume":"174","author":"Panaitescu","year":"2019","journal-title":"Compos. Part B Eng."},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Zouari, M., Devallance, D.B., and Marrot, L. (2022). Effect of Biochar Addition on Mechanical Properties, Thermal Stability, and Water Resistance of Hemp-Polylactic Acid (PLA) Composites. Materials, 15.","DOI":"10.3390\/ma15062271"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"9","DOI":"10.1590\/0104-1428.1722","article-title":"Vegetal fibers in polymeric composites: A review","volume":"25","author":"Pereira","year":"2015","journal-title":"Pol\u00edmeros"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"5801","DOI":"10.1007\/s10570-020-03209-3","article-title":"Nanocrystalline cellulose isolated from different renewable sources to fabricate natural rubber composites with outstanding mechanical properties","volume":"27","author":"Jiang","year":"2020","journal-title":"Cellulose"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"13","DOI":"10.1016\/j.apsusc.2013.02.086","article-title":"Effects of chemical treatments on hemp fibre structure","volume":"276","author":"Kabir","year":"2013","journal-title":"Appl. Surf. Sci."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"1234","DOI":"10.1016\/j.compositesa.2012.02.020","article-title":"Effect of physicochemical structure of natural fiber on transverse thermal conductivity of unidirectional abaca\/bamboo fiber composites","volume":"43","author":"Liu","year":"2012","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"4742","DOI":"10.1016\/j.biortech.2009.04.067","article-title":"Effect of chemical treatments on water sorption and mechanical properties of flax fibres","volume":"100","author":"Alix","year":"2009","journal-title":"Bioresour. Technol."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"613","DOI":"10.1080\/03602559.2010.551379","article-title":"Development of Green Insulation Boards from Kenaf Fibres and Polyurethane","volume":"50","author":"Ibraheem","year":"2011","journal-title":"Polym. Technol. Eng."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"98","DOI":"10.1016\/j.compositesa.2015.08.038","article-title":"A review of recent developments in natural fibre composites and their mechanical performance","volume":"83","author":"Pickering","year":"2016","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"1189","DOI":"10.1016\/j.compositesa.2011.05.003","article-title":"Effect of fibre treatments on interfacial shear strength of hemp fibre reinforced polylactide and unsaturated polyester composites","volume":"42","author":"Sawpan","year":"2011","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"806","DOI":"10.1016\/j.compositesa.2010.03.005","article-title":"Silane coupling agents used for natural fiber\/polymer composites: A review","volume":"41","author":"Xie","year":"2010","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"596","DOI":"10.1016\/j.compositesa.2010.01.006","article-title":"Influence of alkali treatment on the interfacial and physico-mechanical properties of industrial hemp fibre reinforced polylactic acid composites","volume":"41","author":"Islam","year":"2010","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_47","first-page":"1","article-title":"Mechanical Properties of Hemp Fibers and Hemp\/pp Composites: Effects of Chemical Surface Treatment","volume":"11","author":"Suardana","year":"2011","journal-title":"Mater. Phys. Mech."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.compositesa.2014.01.017","article-title":"Novel aligned hemp fibre reinforcement for structural biocomposites: Porosity, water absorption, mechanical performances and viscoelastic behaviour","volume":"61","author":"Baghaei","year":"2014","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"1655","DOI":"10.1177\/0021998306069878","article-title":"Fabrication and Mechanical Properties of Completely Biodegradable Hemp Fiber Reinforced Polylactic Acid Composites","volume":"41","author":"Hu","year":"2007","journal-title":"J. Compos. Mater."}],"container-title":["Polymers"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4360\/14\/11\/2280\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T23:24:20Z","timestamp":1760138660000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4360\/14\/11\/2280"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2022,6,3]]},"references-count":49,"journal-issue":{"issue":"11","published-online":{"date-parts":[[2022,6]]}},"alternative-id":["polym14112280"],"URL":"https:\/\/doi.org\/10.3390\/polym14112280","relation":{},"ISSN":["2073-4360"],"issn-type":[{"value":"2073-4360","type":"electronic"}],"subject":[],"published":{"date-parts":[[2022,6,3]]}}}