A gradient flame retardant strategy to improve the overall performance of polylactic acid/fiber composites

To enhance the flame retardant property of fiber‐reinforced polymer composites without adding more flame retardants, we prepared film stacking composites by maintaining a total flame retardant content of 20% and applying a gradient flame retardant strategy. The gradient composites have been designated as 3113FRPLA/F and 1331FRPLA/F, respectively. 3113FRPLA/F is characterized by an augmented concentration of fire‐resistant additives in the surface layer, while 1331FRPLA/F features a reduced content. 20%FRPLA/F is prepared with a homogeneously distributed flame retardant composition. Results derived from LOI test and cone calorimeter test unequivocally demonstrate that 3113FRPLA/F outperforms both 1331FRPLA/F and 20%FRPLA/F in improving flame retardancy. The LOI value of 3113FRPLA/F is 36.1%, exceeding that of 20%FRPLA/F and there is also a reduction in the pk‐HRR compared with 20%FRPLA/F. It is of interest to note that 3113FRPLA/F exhibits the most effective heat insulation properties while 20%FRPLA/F has the worst, which is reflected by the infrared thermal imaging results. It bears mention that the impact strength and tensile strength of 3113FRPLA/F surpasses that of 20%FRPLA/F. In summary, 3113FRPLA/F, characterized by its increased surface concentration of flame retardants, demonstrates the most superior overall performance.Highlights The characteristics of PLA/fiber composites using a gradient strategy were compared. The LOI value of 3113FRPLA/F is 36.1%, exceeding that of 20%FRPLA/F. 3113FRPLA/F has the best heat insulation effect while 20%FRPLA/F has the worst. The impact strength and tensile strength of 3113FRPLA/F surpasses 20%FRPLA/F. Improving the surface flame retardant concentration increases the overall property.