Abstract
The objective of this study is to assess the efficiency of biobased carbonization agent in intumescent formulations (IFRs) to examine the flame retardant properties of polylactic acid (PLA) composites and to investigate their melt-spinnability. We used phosphorous-based halogen free flame retardant (FR) and kraft lignin (KL) as bio-based carbonization agent. After melt compounding and molding into sheets by hot pressing various fire related characteristics of IFR composites were inspected and were characterized by different characterization methods. It was fascinating to discover that the introduction of 5–20 wt% FR increased the limiting oxygen index (LOI) of PLA composites from 20.1% to 23.2–33.5%. The addition of KL with content of 3–5 wt% further increased the LOI up to 36.6–37.8% and also endowed PLA/FR/KL composites with improved anti-dripping properties. Cone calorimetry revealed a 50% reduction in the peak heat release rate of the IFR composites in comparison to 100% PLA and confirmed the development of an intumescent char structure containing residue up to 40%. For comparative study, IFR composites containing pentaerythritol (PER) as a carbonization agent were also prepared and their FR properties were compared. IFR composites were melt spun and mechanical properties of multifilament yarns were tested. The analysis of char residues by energy dispersive X-ray spectrometry (EDS) and SEM images confirmed that PLA/FR/KL composites developed a thicker and more homogeneous char layer with better flame retardant properties confirming that the fire properties of PLA can be enhanced by using KL as a carbonization agent.
Highlights
Biodegradable polymers from renewable resources have attracted interest due to environmental pollution caused by the disposal of non-degradable polymers derived from finite petroleum reserves [1,2,3,4].Polylactic acid (PLA) is a biobased thermoplastic polymer obtained from bio-resources and it is progressively replacing oil-based polymers and can be used to develop fire resistant products [5,6]
The emission of non-flammable carbon dioxide assisted in diluting the oxygen of the air and flammable decomposed products of the material that were burning whereas the resultant char layer in the condensed phase protected the underlying polymeric material from further burning by restricting the free passage of radiant heat and oxygen
A significant reduction in peak heat release rate (PHRR) was observed when kraft lignin (KL) was added in PLA/APP20 composites as samples containing 3 and 5% (w/w) reduced PHRR to 250 and 210 kW m−2 respectively. These findings indicated that the combined effect of APP and KL yielded a much thicker char structure after burning, preventing the degradation of the composite by restricting the fire passage to the polymer matrix
Summary
Polylactic acid (PLA) is a biobased thermoplastic polymer obtained from bio-resources and it is progressively replacing oil-based polymers and can be used to develop fire resistant products [5,6]. PLA is less flammable than synthetic thermoplastics such as polyethylene terephthalate (PET), with less visible smoke on burning and a lower peak heat release rate [7,8]. PLA is combustible which restricts its applications in industry sectors where flame-retardant materials are required [9,10]. The fire retardancy of PLA can be enhanced by mixing with inorganic additives containing silicon or phosphorous [11,12,13,14]. Intumescent flame retardant (IFR) systems offer a highly effective strategy to enhance the fire retardancy of PLA because a char structure is developed which acts as a shield
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
