Research Progress on Modification of Hydroxypropyl Cellulose

Hydroxypropyl cellulose is an outstanding non-ionic cellulose ether, prepared by reacting pure cellulose with propylene oxide and a small amount of sodium hydroxide [1]. The introduction of hydroxypropyl group significantly weakens the intramolecular and intermolecular hydrogen bonding force of cellulose, thus enhancing its solubility in solution and endowing it with excellent water solubility [2]. Moreover, through continuous research and development, it has been found that hydroxypropyl cellulose has superior edible, thermoplasticity [3], biocompatibility [4] and degradability [5]. As a result, hydroxypropyl cellulose is extensively used as a food additive [6], binder, thickener [7] and stabilizer [8] in numerous fields such as food, environment, daily chemical, textile and others, making significant contributions to the development of these industries. Hydroxypropyl cellulose, although possessing a significant number of hydroxyl groups that could be utilized as reaction groups, it lacks specific functional groups. This necessitates graft modification, which can produce a novel type of hydroxypropyl cellulose with enhanced functions. This significantly broadens its application field and as such, it presents a considerably broader development prospect.

Grafting modification is an efficient technique often employed to enhance the properties of compounds by adapting polar or functional side groups on the polymer chain through free radical polymerization [9]. Consequently, the resulting product displays the advantageous characteristics of both molecules. By utilizing hydroxypropyl cellulose as a raw material, specific functional groups or monomers can be grafted onto it, thereby modifying or augmenting its properties and thereby expanding its scope of application.

Acetoacetyl group graft

Acetoacetyl groups are potent acylation agents capable of converting functional groups such as hydroxyl and amine groups into corresponding acetylation products, which usually enhance the relevant properties of the original compound [10]. Guo M et al. [11] synthesized hydroxypropyl cellulose acetoacetylation graft polymers by grafting acetoacetyl groups from hydroxypropyl cellulose and tested their thermal properties [11]. The research determined that the acetoacetyl groups added altered the crystallization properties of the hydroxypropyl cellulose, increased the heat capacity and boosted the ability to moderate heat effect. This demonstrated the successful grafting and enhancement of the thermoplasticity of the product. Future research can further optimize the reaction conditions to develop more efficient hydroxypropyl cellulose polymers with improved thermoplasticity.

Organosilicone antibacterial agent graft

Hydroxypropyl cellulose exhibits an excellent water absorption property, which is an advantage in some cases, but it also allows for an overgrowth of bacteria, resulting in reduced performance and service life [12]. Thus, it becomes necessary to modify this compound to enhance its antibacterial functionality. Zhang Q et al. [13] obtained Hydroxypropyl Cellulose (m-HPC) with antibacterial properties by grafting a self-made organosilicon antibacterial agent with hydroxypropyl cellulose [13]. It has good antibacterial property and can be used in food, cosmetics and other fields in the future. However, it is worth mentioning that the thermogravimetric experiment shows that the modified hydroxypropyl cellulose has reduced thermal stability. Therefore, enhancing the thermal stability of this novel material is a critical challenge to ensure its enhanced performance in various applications.

Methyl methacrylate and butyl methacrylate graft

Both methyl methacrylate and butyl methacrylate are multifunctional compounds, widely used in many fields such as medical, construction, automotive and electronics [14]. One of their most notable features is its potential to serve as a versatile monomer in the synthesis of polymers or copolymers [15]. This feature allows it to copolymerize with other monomer compounds to create robust chemical bonds and significantly enhance their properties [16]. Guo M et al. [17] prepared hydroxypropyl cellulose grafted polybutyl methacrylate copolymers by emulsion grafting copolymerization [17]. This process significantly improved the thermoplastic characteristics and added resistance to acid and organic reagent corrosion. The outcomes of this study can serve as a useful reference for future research exploring novel, environmentally friendly materials. Moreover, Tan JJ et al. [18] have successfully synthesized a novel copolymer of methyl methacrylate and hydroxypropyl cellulose through emulsion grafting reaction [18]. This copolymer demonstrates excellent resistance to various acid and alkali solutions as well as to organic solvents, but it is shown to have inferior thermal stability, which might be a result of the intense oxidation that takes place within the reaction process. In the future, it is crucial to optimize the preparation methods, such as temperature, PH, etc., to minimize the impact of the grafting reaction on the characteristics of the compounds.

Acrylamide graft

Acrylamide, the most important and simplest acrylamide compound, has a wide range of applications including water treatment flocculants, soil amendments, paper filler adjuvant, chemical grouting agent and fiber modifiers [19]. Shen YC et al. [20] utilized hydroxypropyl cellulose as the backbone and properly grafted polyacrylamide onto it [20]. The resultant polymer displayed excellent water retention and water resistance and therefore is anticipated to prove to be an ideal choice for sand fixation agents. When appropriately applied, it has the potential to assist with the control of land desertification, thereby contributing to the preservation of the environment.

Crosslinking modification is the procedure wherein linear or branched polymer chains are connected into network or branched polymer via covalent bonds, leading to a boost in the strength and stability of materials [21]. This characteristic has made it widely concerned in pharmaceutical, food, environmental governance, catalysis and other fields. Shinya Y et al. [22] modified hydroxypropyl cellulose with cinnamoyl through photo crosslinking technology, and the obtained cinnamylated hydroxypropyl cellulose was found to have good thermal stability and good biocompatibility by thermal analysis and cell proliferation experiments [22]. This indicates that cinnamoyl not only enhances the thermal properties of hydroxypropyl cellulose, but also increases the biocompatibility, making its application range more extensive and providing theoretical basis for its application in medical devices and medical drugs in the future.

In addition to grafting modification and cross-linking modification, hydroxypropyl cellulose is also modified by introducing some specific groups to it. Zhang YY et al. [23] introduced xanthogenated groups and the sulfur group on hydroxypropyl cellulose and the resulting HCX can be used as an adsorbent for water treatment to adsorb heavy metal ions in water, such as Cu²⁺, Ni²⁺ and so on [23]. It is an ideal adsorbent for the purification of industrial wastewater. Because of its non-toxicity and pollution-free, it can be widely developed and utilized in the future.

The development of hydroxypropyl cellulose modification technology is an important strategy to enhance the characteristics of hydroxypropyl cellulose. Through a range of methods including grafting, cross-linking and general chemical modifications, the thermal stability, corrosion resistance and biocompatibility of hydroxypropyl cellulose can be significantly enhanced. Although significant progress has been made, the hydroxypropyl cellulose modification market still has considerable room for growth. Moreover, the application of various modification methods in combination has not been comprehensively explored. Looking into the future, with further improvements in hydroxypropyl cellulose modification technology, it is anticipated that hydroxypropyl cellulose will have a broader range of applications and bring more convenience to our daily lives.

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