Study on the mechanical properties of contemporary composites

การศึกษาคุณสมบัติเชิงกลของสารประกอบชนิดต่างๆ

Name: Jirawut Junkasem

Abstract: Composites are materials that their properties are obtained synergistically from their constituents. Due to the wide variety of materials, myriad combinations of materials can be chosen to arrive at composite materials of diverse properties. In this work, composites are classified into three types, depending on the size of reinforcing materials. The first type is macro-composite, in which the size of the reinforcing fillers is greater than 100 micrometers. The second type is micro-composite, in which the size of the reinforcing fillers is in the micrometer to sub-micrometer range. The third type is nano-composite, in which the size of the reinforcing fillers is less than 100 nanometers. For the macro-composite system investigated in this work, four types of natural fibers from roselle plant (Hibiscus sabdariffa L.), i.e., (1) bast fibers (BF; the weight ratio of bast/core fibers = 100/0), (2) core fibers (Core; the weight ratio of bast/core fibers = 0/100), (3) whole-stalk fibers (WS; the weight ratio of bast/core fibers = 40/60), and (4) core-added whole-stalk fibers (WC; the weight ratio of bast/core = 20/80), were used as reinforcing fillers in injection-molded isotactic polypropylene (iPP) composites. Processibility and mechanical properties of the resulting composites were investigated against the types and the mean sizes of the fibers. The results showed that the highest mechanical properties were observed when BF was incorporated. When WS fibers were used, moderate mechanical properties of the resulting composites were realized. The optimal contents of the WS fibers and the maleic anhydride-grafted iPP compatibilizer that resulted in an improvement in some of the mechanical properties of the resulting composites were 40 and 7 wt %, respectively.

Abstract: For micro-composite system investigated in this work, nylon 4, 6 nanofibers prepared from electrospinning process were used as reinforcing materials in the poly(vinyl alcohol) (PVA) composite films. The nylon 4, 6 as-spun fibers exhibited the average diameter about 116 nm. Successful incorporation of nylon 4, 6 as-spun fibers was verified by scanning electron microscope (SEM). The incorporation of the nylon 4, 6 nanofibers increased the Young’s modulus from 54.31 MPa to 145.75 MPa and further increase with increasing the amount of nylon 4, 6 nanofibers. Halpin-Tsai model was used to compare with the data from experiment. It was found that Hapin-Tsai model can be applied to predict the composite properties especially Young’s modulus. For the nano-composite system instigated in this work, another type of natural nanofillers prepared from α-chitin flakes from Penaeus merguiensis shrimp shells (i.e., α-chitin whiskers) were used as reinforcing fillers in electrospun poly(vinyl alcohol) (PVA) nanocomposite nanofibers. The as-prepared chitin whiskers exhibited lengths in the range of 231-969 nm and widths in the range of 12-65 nm, with the average length and width being about 549 and 31 nm, respectively. Successful incorporation of the chitin whiskers within the as-spun PVA/chitin whisker nanocomposite nanofibers was verified by infrared spectroscopic and thermogravimetric methods. The incorporation of chitin whiskers within the as-spun nanocomposite fiber mats increased the Young’s modulus by about 4-8 times over that of the neat as-spun PVA fiber mat. The influence of the chitin whiskers on dynamic mechanical properties and crystallization behaviour of the PVA matrix in the composites were further investigated by dynamic mechanical analysis (DMA), wide angle X-ray diffraction (WAXD), and differential scanning calorimeter (DSC). The results shown that chitin whisker incorporate in the amorphous region of the PVA and inhibit the crystallization of PVA by forming the hydrogen bonding with PVA chain leading to the reducing in the percent crystallinity of PVA.

Chulalongkorn University. Office of Academic Resources

Address: BANGKOK

Email: cuir@car.chula.ac.th

Name: Pitt Supaphol

Role: advisor

Created: 2008

Modified: 2564-09-10

Issued: 2021-03-07

วิทยานิพนธ์/Thesis

application/pdf

URL: http://cuir.car.chula.ac.th/handle/123456789/67000

eng

DegreeName: Doctor of Philosophy

Level: Doctoral Degree

Descipline: Polymer Science

Grantor: Chulalongkorn University

©copyrights Chulalongkorn University

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