Abstract
Spent coffee grounds (SCG) are a current subject in many works since coffee is the second most consumed beverage worldwide; however, coffee generates a high amount of waste (SCG) and can cause environmental problems if not discarded properly. Therefore, several studies on SCG valorization have been published, highlighting its waste as a valuable resource for different applications, such as biofuel, energy, biopolymer precursors, and composite production. This review provides an overview of the works using SCG as biopolymer precursors and for polymer composite production. SCG are rich in carbohydrates, lipids, proteins, and minerals. In particular, carbohydrates (polysaccharides) can be extracted and fermented to synthesize lactic acid, succinic acid, or polyhydroxyalkanoate (PHA). On the other hand, it is possible to extract the coffee oil and to synthesize PHA from lipids. Moreover, SCG have been successfully used as a filler for composite production using different polymer matrices. The results show the reasonable mechanical, thermal, and rheological properties of SCG to support their applications, from food packaging to the automotive industry.
Highlights
Coffee, as a beverage, is consumed all over the world and is considered a commodity
Lactic acid is a cyclic monomer generally produced from glucose and sucrose fermentation, which can be polymerized into poly(lactic acid) (PLA) through polycondensation or ring-opening polymerization (ROP)
The results show that the Spent coffee grounds (SCG) oil plasticizer (30 wt.%) improved the hydrophobicity and decreased the brittle behavior of the composite
Summary
As a beverage, is consumed all over the world and is considered a commodity. The technique consists of soaking the SCG in hot water, followed by a series of soakings at room temperature with the progressive addition of a base, such as potassium hydroxide or sodium hydroxide, which leads to the precipitation of polysaccharides [26,27,28]. It should be noted that pretreatments can be performed on the SCG before the polysaccharide extraction via water hydrolysis, ultrasound, microwave, or supercritical carbon dioxide (SC-CO2). The synthesis of 2,3-BD occurs from pyruvate with three main enzymes SCG could be used directly for 2,3-BD production, upgrading this lignocellulose-rich waste, since 2,3-BD has several valuable coproducts and can be converted to polymer precursors, as will be described
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