**1. Introduction**

Owing to its versatility and good performance, polylactic acid (PLA) as a biodegradable polymer is regarded as one of the most favorable polymers to substitute petroleumbased plastics [1–3]. The low toughness and poor thermal stability of PLA, however, restrict the usage of PLA in applications, such as food packaging and medical implants [3]. To improve the performance, therefore, several approaches, such as blending with other polymers, mixing with inorganic fillers, and copolymerization, have been suggested by several research groups [4–10]. In particular, the mixing with inorganic additives, such as TiO2, carbon nanotube, ZnO, Al2O3, MgO, and SiO2, was reported to be a useful method to boost the performance of neat PLA [5,7].

Silicon dioxide (SiO2), commonly referred to as silica, which may exist in the amorphous and crystalline structure, was found to be a useful filler for improving the mechanical performance of polymeric materials [11,12]. The silica, as an additive, is used in coatings, food, and biomedical applications. For example, silica as a bio-safe additive can be incorporated along with silver nanoparticles to improve the antibacterial properties and corrosion properties of biomaterials [13–23]. The amorphous silica nanoparticles extracted from natural sources, such as rice husk and fly ash, can be used as a nucleating agent when added to thermoplastic polymers in very low amounts, owing to their large surface area [24]. The improving dispersibility of silica within the PLA matrix during fabrication of PLA/silica composites would lead to enhancing the mechanical, thermal, and rheological

**Citation:** Kaseem, M.; Ur Rehman, Z.; Hossain, S.; Singh, A.K.; Dikici, B. A Review on Synthesis, Properties, and Applications of Polylactic Acid/Silica Composites. *Polymers* **2021**, *13*, 3036. https://doi.org/ 10.3390/polym13183036

Academic Editors: José Miguel Ferri, Vicent Fombuena Borràs and Miguel Fernando Aldás Carrasco

Received: 19 August 2021 Accepted: 7 September 2021 Published: 8 September 2021

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properties of neat PLA [21]. The presence of silanol groups, siloxane bridges, and hydroxyl groups on the silica would facilitate the surface functionalization of silica for biomedical, catalysis, and sensor applications [12].

Therefore, by taking into consideration the attractive properties of silica, the fabrication of PLA/silica composites would be a beneficial procedure to enhance the performance of PLA. To the best of our knowledge, this is the first systematic article deliberating the recent progress in PLA/silica. Thus, this work aims to discuss the recent developments in the field of PLA/silica composites in terms of fabrication, properties, and applications.
