Biodegradable shape-memory polymers and composites

Polymers have recently been making media headlines in various negative ways. To combat the negative view of those with no polymer experience, sustainable and biodegradable materials are constantly being researched. Shape-memory polymers, also known as SMPs, are a type of polymer material that is being extensively researched in the polymer industry. These SMPs can exhibit a change in shape because of an external stimulus. SMPs that are biodegradable or biocompatible are used extensively in medical applications. The use of biodegradable SMPs in the medical field has also led to research of the material in other applications. The following categories used to describe SMPs are discussed: net points, composition, stimulus, and shape-memory function. The addition of fillers or additives to the polymer matrix makes the SMP a polymer composite. Currently, biodegradable fillers are at the forefront of research because of the demand for sustainability. Common biodegradable fillers or fibers used in polymer composites are discussed in this chapter including Cordenka, hemp, and flax. Some other nonbiodegradable fillers commonly used in polymer composites are evaluated including clay, carbon nanotubes, bioactive glass, and Kevlar. The polymer and filler phase differences will be evaluated in this chapter. The recent advances in biodegradable shape-memory polymers and composites will provide a more positive perspective of the polymer industry and help to attain a more sustainable future.

Early Polylysine Release from Dental Composites and Its Effects on Planktonic Streptococcus mutans Growth

The study aim was to assess the effect of incorporating polylysine (PLS) filler at different mass fractions (0.5, 1 and 2 wt%) on PLS release and Streptococcus mutans planktonic growth. Composite containing PLS mass and volume change and PLS release upon water immersion were assessed gravimetrically and via high-performance liquid chromatography (HPLC), respectively. Disc effects on bacterial counts in broth initially containing 8 × 105 versus 8 × 106 CFU/mL Streptococcus mutans UA159 were determined after 24 h. Survival of sedimented bacteria after 72 h was determined following LIVE/DEAD staining of composite surfaces using confocal microscopy. Water sorption-induced mass change at two months increased from 0.7 to 1.7% with increasing PLS concentration. Average volume increases were 2.3% at two months whilst polylysine release levelled at 4% at 3 weeks irrespective of composite PLS level. Early percentage PLS release, however, was faster with higher composite content. With 0.5, 1 and 2% polylysine initially in the composite filler phase, 24-h PLS release into 1 mL of water yielded 8, 25 and 93 ppm respectively. With initial bacterial counts of 8 × 105 CFU/mL, this PLS release reduced 24-h bacterial counts from 109 down to 108, 107 and 102 CFU/mL respectively. With a high initial inoculum, 24-h bacterial counts were 109 with 0, 0.5 or 1% PLS and 107 with 2% PLS. As the PLS composite content was raised, the ratio of dead to live sedimented bacteria increased. The antibacterial action of the experimental composites could reduce residual bacteria remaining following minimally invasive tooth restorations.

Modelling the critical concentration of mixed filler in mastic with synthetic wax

This article presents the results of tests of mastic containing mixed filler (limestone dust/hydrated lime) and Fisher-Tropsch synthetic wax. Synthetic wax content was controlled up to 3% (w/w). The ratio of filler in the bitumen was from 0.5 to 3 (w/w), with hydrated lime content of up to 30% w/w. The rheological properties of different mastic compositions were determined with a rheometer equipped with two parallel plates at 60°C using oscillating load. The primary purpose of the article was to determine the nature of mastic stiffness changes in the context of using hydrated lime and synthetic wax as the filler. Consequently, the article proposes a method for evaluation of the critical value of the filler phase in the phase of bitumen modified with synthetic wax. The proposed model of the mathematical function was used to determine the nature of mastic structuring throughout the range of the experiment. The model was also used to determine the critical concentration of the filler in the bitumen phase. It was demonstrated that below the critical filler concentration the mastic behaved in a significantly different manner from the behaviour observed above this critical concentration. When the critical concentration of the filler was exceeded, it resulted in an excessive increase of mastic stiffness, which was considered in the model.

MIXING SEQUENCE IN NATURAL RUBBER CONTAINING ORGANOCLAY AND NANO–CALCIUM CARBONATE TERNARY HYBRID NANOCOMPOSITES

ABSTRACT Rubber nanocomposites containing one type of nanofiller are common and are widely established in the research field. In this study, natural rubber (NR) based ternary nanocomposites containing both calcium carbonate and organoclay have been characterized on the basis of morphology, cure characteristics, and physico-mechanical behavior. Natural rubber nanocomposite samples containing modified silicate (Cloisite 15A) and also nano-carbonate calcium were prepared using a laboratory internal mixer. The effect of the mixing sequence on the morphology and mechanical properties of the samples was investigated. Based on results of morphology and mechanical properties, the dual fillers phase nanocomposites (hybrid nanocomposite) perform better in comparison with single filler phase nanocomposites. The reinforcing capability of nano-CaCO3 and organoclay in NR was characterized by means of cure rheometry, morphology, and mechanical properties. NR/single filler phase and two filler phase nanocomposites were prepared by simple melt mixing method. Concentration of nano-CaCO3 and organoclay in NR was 10 and 5 parts per one hundred parts of rubber by weight, respectively. The microstructure and homogeneity of the compounds was confirmed by studying the dispersion of nanoparticles in NR via X-ray diffraction and field emission scanning electron microscopy. A more pronounced effect was achieved by using dual filler based nanocomposites as compared with single filler phase nanocomposites. The obtained results reveal that hybrid nanocomposites have more adequate morphology, rheometery, and mechanical behaviors as well as swelling resistance. The effect of mixing sequence of fillers has been studied in detail. Simultaneous addition of the two nanofillers to the NR compound would lead to better nanocomposite properties compared with other mixing sequences. Also, the results show that the mixing sequence of these nanofillers in NR has little effect on the performance of the nanocomposite.