1. Introduction
Fossil resources are used for various applications, including energy generation, running transportations, polymer, and plastic synthesis [
1]. Fossil resources are non-renewable, and they also produce numerous harmful substances, such as benzene and hydrogen sulfide. With the advancement of society and the increasing awareness of environmental protection, there is considerable focus on the use of alternative renewable energy sources. Polyurethane foam (PUF) is widely used as an acoustic material, due to its superior sound-absorbing properties, vibration damping, and robustness in automobile industry [
2,
3]. The pure petroleum-based polyurethane foam (PPUF) consumes numerous fossil resources. In addition, it causes great damage to the environment.
Raw materials for synthetic vegetable oils, include common soybean oil, castor oil, palm oil, etc. Sonnenschein et al. [
4] prepared a flexible PUF by means of soybean oil-based polyols and toluene diisocyanates. Bonnaillie et al. [
5] used Epoxidized soybean oil to produce a thermosetting elastic foam of high mechanical properties through a carbon dioxide foaming process. Spontón et al. [
6] found that biodegradability of flexible PUF is greatly improved after being modified by castor oil. The effect of hydroxyl in the polyols on mechanical properties was studied when flexible PUF was prepared with Rapeseed oil [
7,
8,
9]. Marcovich et al. [
10] and Prociak et al. [
11] mixed palm oil polyols and polyether polyols to prepare polyurethane foams. Zhang et al. [
12] investigated the mixed situation of soy-castor oil-based polyols and petroleum-based polyols to evaluate the miscibility.
Tung oil is a suitable raw material to produce high hydroxyl content polyols in the synthesis of PUF. Tung oil is a renewable resource. It can be easily extracted because tung tree is widely distributed in China. In addition, tung oil offer a priori of possibilities for biodegradation [
13]. Among various available oil, tung oil is a conjugated drying oil. Tung oil has a high iodine value and contains a conjugated triene on the triglyceride molecule [
14]. Furthermore, tung oil has the advantages of faster drying time, high corrosion resistance, and high hardness as a result of high levels of unsaturation. Therefore, tung oil is an important industrial oil with a wide range of applications in paints, ships, and materials [
15]. To the best of our knowledge, very few research studies have been done on tung oil-based flexible polyurethanes foam (TOPUF), especially their acoustic properties.
There are numerous modification methods to improve the performance of PUF, including physical modification methods (alloying, filling, etc.) and chemical modification methods (interpenetrating polymer network, copolymerization grafting crosslinking, etc.) [
16,
17,
18,
19,
20]. Adding filler is a common modification method because it is simple and relatively inexpensive. From the perspective of properties, fillers are divided into organic and inorganic fillers. They contain granules, flakes, and fibrous fillers in terms of morphology. Sung et al. [
21] investigated the morphological and physical properties of PUF with addition of inorganic fillers including Talc, Zinc Borate, and Aluminum Hydroxide. Chen et al. [
22] added bamboo leaf particles to the PUF to ameliorate the acoustic properties. Santos et al. [
23] described the influence of the concentration of lignin as a filler of PUF for crude oil sorption. Zhang et al. [
24] prepared castor oil-based PUF by self-rising method with soy protein isolate as reactive reinforcing filler. Merlini et al. [
25] used graphene nanoplatelets, expanded graphite, multiwall carbon nanotubes, and carbon black filler in fabricating thermosetting PUF for improving mechanical property.
The use of organic materials to modify PUF takes full advantage of natural resources. Miscanthus lutarioriparius (ML) is widely distributed in the middle and lower reaches of the Yangtze River in China. It is considered to be one of the most promising second-generation biomass resources [
26]. Miscanthus lutarioriparius contains high lignocelluloses and carbohydrate with 50% content of fiber. It can be cultivated under different soil and climatic conditions [
27]. Nowadays, it is often used in paper and fiberboard because of its excellent fiber quality. ML is also suitable as an organic filler to be added to polymers due to its stable structure and high cellulose content. So far, as far as we know, ML has not been used as a kind of filler for PUF in current researches. In addition, there are few research results on the effects of fillers on the acoustic properties of PUF.
In this study, we reported the effect of ML filler on acoustic and mechanical properties of TOPUF. Firstly, tung oleic acid-based polyol (TOAP) was used to replace a part of petroleum materials to prepare TOPUF. An amount of 0.3–1.5 wt% of ML was loaded into TOPUF to improve the acoustic properties, especially in low frequency rang. Miscanthus lutarioriparius in strip and powder form were used to prepare TOPUF with addition of ML (TOPUFL). Then, PUF were characterized by means of Fourier transform infrared (FTIR) and SEM. Then, we determined the cell morphology, acoustic parameters, and mechanical properties of TOPUFL. Finally, the TOPUFL was compared with TOPUF and PPUF.
4. Conclusions
A novel polyurethane acoustic material modified with ML of different forms (stripe and powder) and content (0.3–1.5 wt%) were prepared to improve acoustic performance in this paper. A noticeable improvement of sound absorption properties can be achieved by adding ML as fillers into PU foams. The results illustrate that the addition of ML has an influence on the size of the cavity, surface density, pores, as well as the wall thickness. The acoustic performance of TOPUF with ML powders is superior to ML strips on account of the uniformity of the combination of ML powder filler and TOPUF. It has been found that small cavities form, and the size of pores decreases with the increasing of ML powders. These structural changes affect the absorption and reflection of sound waves in the cavity. The results showed that TOPUF with 0.3 wt% of ML possess an optimal acoustic performance, whose average sound absorption coefficient and transmission loss can reach 0.518, and 19.05 dB, respectively. In addition, the porosity is 0.81, and the flow resistance rate is 96.68 kPa/m2. Moreover, the pressure resistance of ML will increase with the addition of ML powders. Its compression strength can be increased by three times compared with TOPUF. In contrast with PPUF, the TOPUFL has excellent low-frequency sound absorption performance, sound insulation performance, and mechanical properties. TOPUF, containing large numbers of biological components, are more environmentally friendly, and have a more comfortable odor. At the same time, TOPUF with the addition of ML, can make the full use of ML and reduces the waste of nature resources. To sum up, TOPUF adding ML can be a good acoustic packaging material with infinite application prospects. The results and method can be used as guidance for future design of acoustic materials.