Organic-Inorganic Hybrid Materials from Vegetable Oils

Abstract

The production of materials based on fossil resources is yielding more sustainable and ecologically beneficial methods. Vegetable oils (VO) are one example of base materials whose derivatives rival the properties of their petro-based counterparts. Gaps exist however and one way to fill them is by employing sol-gel processes to synthesize organic-inorganic hybrid materials, often derived from silane/siloxane compounds. Creating Si─O─Si inorganic networks in the organic VO matrix permits the attainment of necessary strength, among other property enhancements. Consequently, many efforts have been directed to optimally achieve organic-inorganic hybrid materials with VOs. However, compatibilization is challenging, and desirable conditions for matching the inorganic filler in the organic matrix remain a key stumbling block toward wider application. Therefore, this review aims to detail recent progress on these new hybrids, focusing on the main strategies to polymerize and functionalize the raw VO, followed by routes highlighting the addition of the inorganic fillers to obtain desirable composites.

Keywords: hybrids; inorganic network; sol–gel process.

Figure 1

General example of a VO structure made of triglyceride.

Figure 2

World production of vegetable oils obtained from USDA, Oil crops Data: Yearbook Table, for the years 2023/2024.

Figure 3

Example of actives groups present on VOs.

Figure 4

Schematic of the sol–gel process involving two steps. First, the catalyzed hydrolysis occurs followed by the condensation to form the network.

Figure 5

Formation of the Si─O─Si network from a silylated polymer. (In blue: polymer, orange triangle: silane functions).

Figure 6

Structure of some commonly used silanes.

Figure 7

Schematic of the different organic–inorganic hybrids described in this review. (Left) organic–inorganic hybrid of raw VO, described in Section 3. (Middle) organic–inorganic hybrid of polymerized VO, described in Section 4. (Right) Formation of composites, described in Section 5.

Figure 8

Reaction path for epoxidation of a double bond.

Figure 9

Reaction between 3‐(trimethoxysilyl)‐1‐propanethiol and VO used by Bexell et al.^{[ 58 ]}

Figure 10

Condensation and curing process of a silane on a substrate, with available ‐OH functions.

Figure 11

Structures of the modified linseed oil and tung oil used by Soucek's group.^{[ 59 ]} In orange is highlighted the end capped silane.

Figure 12

Structure of the modified fatty amide obtained from castor oil used by Agarwal group to create an antibacterial film.^{[ 69 ]}

Figure 13

Possible ways to polymerize a VO: in pink from the epoxy function, in green from the hydroxyl function, and in blue from the double bond.

Figure 14

Structure of the two possible products that can be obtained from the reaction of VO with amine: 1) ring opening of epoxy groups and 2) trans‐amidation of the triglyceride.

Figure 15

Reaction between a diol and a diisocyanate to synthesize a polyurethane, showing the urethane linkage in purple.

Figure 16

Explanation of the three ways to obtain PU‐based hybrid materials. 1. Synthesis of a PU in the first step, then the addition of the silane. 2. Synthesis of a polyol capped with a silane, used to form the PU in the second step. 3. Synthesis of an isocyanate capped with a silane, used to form the PU in the second step. At the end, all the VO‐based PU are end‐capped with a silane and can be moisture cured via the sol–gel process to fabricate hybrid materials.

Figure 17

Waterborne polyurethane dispersion condensed with moist air to create a film. Before moisture curing, the silane functions are not linked to each other. After the moisture curing Si─O─Si linkages are formed between the silane functions.

Figure 18

Structure of the diol synthesized by Shaik's group from APTMS and GPTMS.^{[ 93 ]}

Figure 19

Description of the synthetic route for organic–inorganic hybrid PU used by Shaik's group.^{[ 97 ]}

Figure 20

Reaction between a cyclic carbonate and a diamine to synthesize polyhydroxyurethanes.

Figure 21

Structure of the end‐capped VO used by Gharibi et al.^{[ 98 ]}

Figure 22

Procedure used to synthesize green polyhydroxyurethanes from soybean oil and lignin.^{[ 106 ]}

Figure 23

Modified acrylated soybean oil used by Colak et al.^{[ 108 ]}

Figure 24

Structure of modified silica nanoparticles. R₁ can be chosen to have the needed chemical function to be involved in the next step of the synthesis (i.e., carbonate for PHU synthesis, for example).

Figure 25

Example of the surface modification of other fillers with silane moieties using the hydroxyl functional groups present on the surface of the fillers. In blue, a modified basalt fiber is shown, in yellow zinc oxide and in green titanium oxide. R₁ is chosen to be the desired functionality to help the compatibilization of the filler to the polymer matrix.

Figure 26

Summary of the different ways to obtain cured hybrid Organic–Inorganic materials from VOs employing a sol–gel process. (Left) From raw VO mixed with either neat silane: no formation of covalent bond, only a Si─O─Si network (in orange) or functional silane: formation of covalent bonds between the VO and the siloxane and formation of a Si─O─Si network; (Middle) From polymerized VOs with either neat or functional silanes (same explanation as in left panel); (Right) Composites: functionalization of the filler surface with a silane using the sol–gel method and then mixed into a VO.