Experimental composites of polyacrilonitrile-electrospun nanofibers containing nanocrystal cellulose

Highlights

• Experimental nanofiber-reinforced resin composites were produced.

• The effects of nanocrystal cellulose addition to the nanofibers were evaluated.

• Mechanical properties were evaluated.

• A toughening effect was achieved with the addition of NCC-containing nanofibres to resin.

Abstract

Objective

To test the effects of addition of polyacrilonitrile (PAN) nanofibers and nanocrystal cellulose (NCC)-containing PAN nanofibers on flexural properties of experimental dental composites.

Methods

11 wt% PAN in dimethylformamide (DMF) solution was electrospun at 17.2 kVA and 20 cm from the collector drum. NCC was added to the solution at 3 wt%. Fiber mats were produced in triplicates and tested as-spun. Strips (5 cm × 0.5 cm) were cut from the mat in an orientation parallel and perpendicular to the rotational direction of the collector drum. Tensile tests were performed and ultimate tensile strength (UTS), elastic modulus (E) and elongation at maximum stress (%) were calculated from stress/strain plots. Fiber mats were then infiltrated by resin monomers (50/50 BisGMA/TEGDMA wt%), stacked in a mold (2 × 15 × 25) and light-cured. Beams (2 × 2 × 25 mm) were cut from the slabs and tested in a universal testing machine. Data were analyzed by multiple t-test and one-way ANOVA (α = 0.05).

Results

Addition of 3% NCC resulted in higher tensile properties of the fibers. Fibers presented anisotropic behavior with higher UTS and E when tested in perpendicular orientation. The incorporation of 3% NCC–PAN nanofibers resulted in significant increase in work of fracture and flexural strength of experimental dental composite beams.

Significance

NCC was found to be a suitable nanoparticle to reinforce experimental dental composites by incorporation via nanofiber. This fundamental study warrants future investigation in the use of electrospun nanofibres as a way to reinforce dental composites.

Introduction

Di-methacrylate composites are widely and successfully used in clinical dentistry as the material of choice for most of the procedures requiring reconstruction of missing tooth structure [1]. Over longer-term, bulk fracture of the restorative material has been regarded as one of the major cause of failure that requires replacement [2,3]. To overcome the problem, reinforcement of the material to make it more durable is desirable. Among several approaches to address that issue, strengthening of dental composites with electrospun nanofibers has been recently the focus of some research. Fibers have been incorporated into resin matrices either as particles reconditioned from fibers [4,5] or as continuous fibers [[6], [7], [8]]. Although some disagreement exists from the reports [9,10], it appears that the general conclusions indicate that the presence of nanofibers increases the energy necessary to break dental composites.

Electrospinning technology made possible the combination of nanoparticles with nanofibers, creating the so-called multifunctional composite nanofibers [11]. Such technique can be used to increase the mechanical properties of regular polymeric nanofibers significantly [12,13]. Up to date, few studies have tried to investigate the effects of nanofibrous composites as reinforcing agents for dental composites [14,15].

Nanocrystalline cellulose (NCC) is a renewable, biocompatible, and extremely strong rod-like particle [16]. It has been shown that low concentrations of NCC can remarkably increase mechanical properties of electrospun nanofibers [17,18], and glass-ionomer cements [19].

Polyacrilontrile nanofibers are known for its high toughness and high strength at low weight ratio [20,21], and have already been demonstrated to reinforce dental composites positively [6]. However, to the best of our knowledge, there is no report combining NCC and PAN to reinforce dental composites. Expectedly, the use of a particle-reinforced nanofiber to reinforce a resin matrix would combine the effects to result in a fiber-reinforced composite with superior properties. We have previously demonstrated that the tensile properties of PAN nanofibers could be significantly improved by the addition of 1–3% NCC to the electrospun polymer [22]. In this study, we tested the hypothesis that the addition of NCC-reinforced PAN nanofibers to di-methacrylate resin blends could improve the flexural properties of the resultant composite. The null hypothesis tested was that there would be no effect on flexural properties of experimental dental composites when reinforced with PAN nanofibers and NCC-containing PAN nanofibers.