Tea is one of the most common and widely consumed beverages, taking the second position just after drinking water. Tea is popular for its outstanding health-promoting effects such as anti-inflammatory, cardiovascular preventive, anticancer, antidiabetic, anti-obesity, neuro-protective, and antioxidant activities. The global demand of tea is increasing remarkably and it will continue to grow over the next decade also. In order to meet such growing demand, the worldwide tea production is rising drastically which in turn results in the generation of enormous amounts of tea waste causing serious environmental issues. Therefore, the potential and sustainable utilization of tea waste is of high research endeavour. In this present work, the various aspects of tea waste such as its worldwide production, compositions, bioactive compounds of medicinal importance present in tea waste and the formation of different value-added materials from tea waste are comprehensively reviewed. Moreover, the emerging applications of tea waste in different fields including environmental remediation, energy generation, fabrication of polymer composites and preparation of electrical devices for the purpose of energy storage are elaborated in details. This review article will be beneficial to the researchers for acquiring an in-depth knowledge on the sustainable and versatile applications tea waste as a cost-effective and environmental-friendly source of biomass.

Potential and sustainable utilization of tea waste: A review on present status and future trends

Due to environmental concern and depletion of fossil fuel, research on biopolymer is gaining interest among researchers. Polylactic acid (PLA) is produced from renewable resources. PLA has high ten...

An overview of toughening polylactic acid by an elastomer

Composite materials are emerging as a vital entity for the sustainable development of both humans and the environment. Polylactic acid (PLA) has been recognized as a potential polymer candidate with attractive characteristics for applications in both the engineering and medical sectors. Hence, the present article throws lights on the essential physical and mechanical properties of PLA that can be beneficial for the development of composites, biocomposites, films, porous gels, and so on. The article discusses various processes that can be utilized in the fabrication of PLA-based composites. In a later section, we have a detailed discourse on the various composites and nanocomposites-based PLA along with the properties’ comparisons, discussing our investigation on the effects of various fibers, fillers, and nanofillers on the mechanical, thermal, and wear properties of PLA. Lastly, the various applications in which PLA is used extensively are discussed in detail.

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Critical Review on Polylactic Acid: Properties, Structure, Processing, Biocomposites, and Nanocomposites

Advances in bioconversion of spent tea leaves to value-added products.

Pineapple has been known as one of the most popular tropical fruits in Vietnam with a production of over 674,000 t in 2018. However, by-products from pineapple cultivation account for approximately 65 % of the fresh fruit weight and are mostly being dumped, decomposed or burnt now. Therefore, it has recently raised great concern about environmental pollution. For the first time, extracted fibres from pineapple leaves being utilized for developing successfully eco-friendly and cost-effective pineapple fibres (PFs) aerogels by using polyvinyl alcohol as a cross-linker and following a freeze-drying method. The morphology of the PFs aerogels can be controlled well by changing the PFs concentration (0.5 - 2.0 wt%). The PFs aerogels exhibit extremely low densities (12.7 - 32.6 kg/m3) and high porosities (96.9 - 98.8 %). The BET result shows that the surface area of the PFs aerogel has up to 5.6 m2/g and their pore size of 1.3 - 2.2 nm. The developed PFs aerogels show extremely low thermal conductivities ranging from 0.030 to 0.034 W/m.K. Due to the low Young’s modulus values ranging from 0.47 - 7.86 kPa, the PFs aerogels are flexible and can be used for heat insulation of the buildings as well as food preservation.

Morphology Control and Advanced Properties of Bio-Aerogels from Pineapple Leaf Waste

An awareness to sustain world’s green environment have triggered many efforts to use agricultural wastes as sources of fibres in pulp and paper making industries. In this research, tea waste/kapok fibre composite papers at various amounts of kapok contents were prepared. Tea waste, a by-product from tea industry, was treated with sodium hydroxide (NaOH) solution to remove non-cellulosic substances such as lignin, wax and hemicellulose. It was found that the tea waste papers treated with 15 wt% - 25 wt% NaOH solutions exhibited good tear indexes. Addition of kapok fibre into the tea waste had reduced the tear indexes of the composite papers. Higher kapok contents caused the entanglement of their long fibres, resulting in agglomeration of the fibres throughout the tea waste matrix. This was proven by the images of scanning electron microscopy. However, the water repellent properties of the composite papers were improved at an average of 52.3 % with respect to that of pure tea waste paper. The hydrophobic nature of the kapok fibre was responsible for the results. Overall, tea waste/kapok fibre composite has offered an improved paper property, where each fibre compensated the weakness of its counterpart. This indicates with agrowastes can be manipulated in such way to meet the requirements for pulp and paper making industries.

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Development of tea waste/kapok fiber composite paper

Natural rubber toughened by polylactic acid/graphene (PLA/NR/GR) biocomposite was prepared by two different processes known as the in-situ melt mixing process (conventional) and the integration of latex compounding masterbatch and melt mixing process. These two processes were employed to compare the state of graphene dispersion and distribution in the biocomposite. Good dispersion and distribution of nanographene is a key factor that can enhance or change the properties of the nanocomposite. The objectives of this work are to evaluate the effect of different processes and graphene content on the mechanical, and morphological of PLA/NR/GR biocomposites. The composition of PLA/NR blend was fixed at 80/20 wt% and the graphene content was varied from 0.1 - 0.4 parts per hundred (phr). The integration process produced the PLA/NR/GR nanocomposite with better mechanical properties compared with the conventional process due to a better state of GR dispersion in the nanocomposite. The tensile strength was slightly improved at lower GR content indicating that GR is effective in increasing strength of toughened PLA nanocomposite. NR improved the impact strength of PLA biocomposites with a sacrifice of tensile strength. The results also revealed that the PLA/NR blend was reinforced and toughened simultaneously by GR, which is extraordinary as compared with many reported nanofiller-reinforced PLA composites. The simultaneous improvement in both strength and toughness could be attributed to the homogeneous dispersion of GR in PLA/NR matrix. The integration process had given a promising method to homogeneously dispersed GR in the polymer matrix which in turn can become a successful method for producing graphene nanocomposite.

Properties enhancement of polylactic acid biocomposite

Concentration technique via progressive freeze concentration was applied to increase the concentration of coconut water for commercialisation. The process will eliminate portion of water from coconut water and retain pure nutritional compound with high sugar content. To obtain the optimum condition, which is the objective of this study, optimisation process was conducted using Response Surface Methodology (RSM) through STATISTICA Software. RSM was utilised to optimise the process parameters for effective partition constant(K) in progressive freeze concentration (PFC) of the coconut water. The effects of circulation flowrate, circulation time, initial solution concentration and coolant temperature on effective partition constant were observed. Results show that the data adequately fit the second-order polynomial model. The linear and quadratic independent variables, circulation flowrate, circulation time, initial concentration and coolant temperature have significant effects as well as interactions on the effective partition constant. It was observed that the optimum process parameters within the experimental range for the best K would be with circulation flowrate of 3,400 mL/min, circulation time of 23 min, initial concentration of 3.4 % Brix and coolant temperature of -7 °C. Under these conditions, the K can be enhanced up to 0.3.

Process Optimisation of Effective Partition Constant in Coconut Water via Progressive Freeze Concentration

Pineapple Leaves Fiber (PALF) Crosslinked with Chitosan for Antimicrobial Properties Norazreen A. Jalil, Norfhairna Baharulrazi, Zurina Mohamad, Muhammad Mustapha, Siti Hajjar Che Man* Bioproses and Polymer Engineering Department, Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia Department of Mechanical Engineering, Politeknik Ibrahim Sultan, KM 10, Jalan Kong Kong, 81700 Pasir Gudang, Johor, Malaysia sitihajjar@utm.my

Mohamad Zurina

Papers

Development of tea waste/kapok fiber composite paper

Properties enhancement of polylactic acid biocomposite

Process Optimisation of Effective Partition Constant in Coconut Water via Progressive Freeze Concentration

Pineapple leaves fiber (palf) crosslinked with chitosan for antimicrobial properties