The Use of Computed Tomography in the Study of Microstructure of Molded Pieces Made of Poly(3-hydroxybutyric-co-3-hydroxyvaleric acid) (PHBV) Biocomposites with Natural Fiber

Abstract

In order to determine the structure homogeneity of biocomposites filled with fibers, as well as the evaluation of fibers’ arrangement and their orientation on the sample cross-section at varied injection rates, a study was conducted using computed tomography (CT). The main advantage of this test is the fact that in order to assess the microstructure on cross-sections, the samples do not have to be processed mechanically, which allows for presenting the actual image of the microstructure. The paper presents the issues of such tests for the biocomposite of poly (3-hydroxybutyric-co-3-hydroxyvaleric acid) (PHBV)-hemp fibers. It should be emphasized that CT scanning of PHBV-hemp fiber biocomposites is quite difficult to perform due to the similar density of the fibers and the polymer matrix. Due to the high difficulty of distinguishing fibers against the background of the polymer matrix during CT examination, a biocomposite containing 15% hemp fibers was analyzed. The samples for testing were manufactured using the injection molding process at variable injection rates, i.e., 10, 35 and 70 cm3/s. The images obtained by computed tomography show the distribution of hemp fibers and their clusters in the PHBV matrix and the degree of porosity on the sample cross-section. There were significant microstructural differences for the samples injected at the highest injection rates, including, among others, the occurrence of a smaller number of fibers and pores on the surface layer of the molded piece. The phenomenon observed was verified by testing chosen mechanical properties, shrinkage and water absorption of the samples. Some properties improved with an increasing injection rate, while others deteriorated and vice versa. An analysis of biocomposites’ microstructures using computed tomography provides a wide range of possibilities for future research, including an assessment of the structure of the molded parts. These tests may allow one, for example, to detect the cause of molded piece properties decreasing in a specific area as a result of a high degree of fiber disorientation, as well as the defects resulting from high porosity of the material. Such analyses can be particularly useful for producers that deal with the injection molding of pieces molded with specific properties.

The Mechanical Properties Prediction of Poly [(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) Biocomposites on a Chosen Example

“…Manufacturing of PHBV biocomposites filled with hemp fiber and the material data of hemp fiber are presented in the authors’ research work [ 41 , 42 , 43 , 46 ]. The work involved the production of a PHBV biocomposite with a mass fraction of 30% of hemp fiber.…”

“…The current trend related to counteracting the problem of management of petrochemical plastic waste prompts the development of modern polymer materials [ 36 , 37 , 38 , 39 , 40 ], whose properties are initially unknown. An example of this can be the poly [(3-hydroxybutyrate)-co-(3-hydroxyvalerate)]—(PHBV)-hemp fiber (PHBV-hemp fiber) biocomposite, which is characterized by its natural origin and the possibility of full biodegradation [ 41 , 42 , 43 ]. Due to the fact that hemp fibers are natural ones, they are characterized by a lower repeatability and homogeneity of the structure, which results in a greater dispersion of properties.…”

Properties of Basalt Fiber Core Rods and Their Application in Composite Cross Arms of a Power Distribution Network

“…As shown in Figure 5, a sample measuring 0.4 mm × 0.4 mm × 0.8 mm was drilled on the center of the core rod for observations, and the two types of materials were scanned with a nanoVoxel-3000 high-resolution computed tomography system (CT, Sanying Precision Instruments Co., Ltd., Tianjin, China) with a voxel size of 0.0475 µm. Then, three-dimensional (3D) structural modeling was performed for the scanning results to determine the difference in pore size and pore distribution between the two types of materials [18].…”