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Y. Qin et al.
Keywords Recycled PET · Virgin PET · Melt spinning · Thermal behaviour ·
Viscosity · Surface morphology · Mechanical property · Semi-empirical equation
1 Introduction
In the 1970s, there was an unprecedented usage of poly(ethylene terephthalate) (PET)
as a packaging material, when one highly oriented PET container was produced
from high-molar-mass PET by the Du-Pont company [1]. Since then, many factors,
including good mechanical properties, chemical resistance, clarity, thermal stability, light-weight, easy disposability and recyclability, have been realized and have
motivated PET to be a preferable material in the packaging industry [2–9]. PET is
extensively used for the manufacturing of liquid containers, especially PET bottles
used for mineral water, bubble water, carbonated drinks, as well as other beverages.
As well documented, the proportion of PET bottles in the global PET resin requirement is 83–84% [10]. The growth of PET consumption together with the slow natural
decomposition rate of PET has resulted in a serious environmental pollution problem. There is also a low utilization efficiency of post-consumer PET bottles [11, 12].
Due to growing attention to environmental protection and the better utilization of the
resource, PET recycling has played a significant role in the global supply chain of
PET bottles [13, 14]. The recycling process of PET bottles would provide the potential to reduce fossil fuel and energy consumption while also reducing greenhouse
gas emissions [15].
Techniques for recycling PET bottles consist of chemical recycling, physical recycling, and energy recovery (i.e., burning) [8, 16–19]. Chemical recycling is a highcost method which includes the depolymerization of the post-consumer PET waste
into monomer units or randomly into chain fragments. The formation of gas byproducts is normally associated with this depolymerization process. The obtained
monomers are then purified using the distillation method and dried for generating
new polymers. In physical recycling, namely mechanical recycling, PET bottles are
separated from other polymer bottles and contaminations, and then are washed before
the smashing process. Eventually, PET bottle flakes or re-extruded PET granules from
extrusion moulding are obtained. This physical recycling process causes deteriorations of properties to some extent, for instance, the discolouration or molar mass loss
resulting from chain scission or hydrolysis with the existence of water, acidic pollutions or other polymers. Therefore, until now only a small amount of recycled PET
from post-consumer bottles are employed for the manufacture of original products,
while the majority of them are employed to produce fibres for blankets or clothing,
without recycling again after use [20].
In the past two decades, a considerable amount of literature has been published on
the manufacturing of fibres from recycled PET waste through different processing
routes, such as melt spinning [1, 18, 19, 21–26], electrospinning [9, 27–29], or newlyinvented centrifugal spinning [30]. As known, the physical properties of fibres are
significant criteria to evaluate their potential applications. Focusing on the most
Y. Qin et al.
Keywords Recycled PET · Virgin PET · Melt spinning · Thermal behaviour ·
Viscosity · Surface morphology · Mechanical property · Semi-empirical equation
1 Introduction
In the 1970s, there was an unprecedented usage of poly(ethylene terephthalate) (PET)
as a packaging material, when one highly oriented PET container was produced
from high-molar-mass PET by the Du-Pont company [1]. Since then, many factors,
including good mechanical properties, chemical resistance, clarity, thermal stability, light-weight, easy disposability and recyclability, have been realized and have
motivated PET to be a preferable material in the packaging industry [2–9]. PET is
extensively used for the manufacturing of liquid containers, especially PET bottles
used for mineral water, bubble water, carbonated drinks, as well as other beverages.
As well documented, the proportion of PET bottles in the global PET resin requirement is 83–84% [10]. The growth of PET consumption together with the slow natural
decomposition rate of PET has resulted in a serious environmental pollution problem. There is also a low utilization efficiency of post-consumer PET bottles [11, 12].
Due to growing attention to environmental protection and the better utilization of the
resource, PET recycling has played a significant role in the global supply chain of
PET bottles [13, 14]. The recycling process of PET bottles would provide the potential to reduce fossil fuel and energy consumption while also reducing greenhouse
gas emissions [15].
Techniques for recycling PET bottles consist of chemical recycling, physical recycling, and energy recovery (i.e., burning) [8, 16–19]. Chemical recycling is a highcost method which includes the depolymerization of the post-consumer PET waste
into monomer units or randomly into chain fragments. The formation of gas byproducts is normally associated with this depolymerization process. The obtained
monomers are then purified using the distillation method and dried for generating
new polymers. In physical recycling, namely mechanical recycling, PET bottles are
separated from other polymer bottles and contaminations, and then are washed before
the smashing process. Eventually, PET bottle flakes or re-extruded PET granules from
extrusion moulding are obtained. This physical recycling process causes deteriorations of properties to some extent, for instance, the discolouration or molar mass loss
resulting from chain scission or hydrolysis with the existence of water, acidic pollutions or other polymers. Therefore, until now only a small amount of recycled PET
from post-consumer bottles are employed for the manufacture of original products,
while the majority of them are employed to produce fibres for blankets or clothing,
without recycling again after use [20].
In the past two decades, a considerable amount of literature has been published on
the manufacturing of fibres from recycled PET waste through different processing
routes, such as melt spinning [1, 18, 19, 21–26], electrospinning [9, 27–29], or newlyinvented centrifugal spinning [30]. As known, the physical properties of fibres are
significant criteria to evaluate their potential applications. Focusing on the most