塑料污染已经对生态系统和人类健康造成严重影响。我国是世界上塑料产量、消费量以及废物量最大的国家之一，我国每年废塑料量约是3000万吨。在第75届联合国大会上习近平总书记提出我国力争于2030年前实现“碳达峰”与2060年前实现“碳中和”的目标。塑料行业是发展国民经济的基础行业，也是高碳排放行业，更是实现双碳目标的重点行业。此外，2020年我国颁发了《关于进一步加强塑料污染治理的意见》（即“限塑令”），这对塑料行业的发展产生了重要影响。然而，限塑令与双碳目标背景下塑料全生命周期的减废降碳机制与关键减排路径是未知的。另外塑料生命周期系统往往涉及社会、经济、资源和环境等众多因素，这为塑料生命周期系统的减废降碳协同管理带来明显的复杂性和不确定性。因此，本论文综合采用物质流分析模型、基于过程的生命周期评价模型、情景分析和蒙特卡洛模拟等理论和方法，首先，构建我国塑料全生命周期物质流分析与温室气体排放核算模型，揭示塑料流量存量以及温室气体排放的历史动态演变规律；然后，进一步剖析未来限塑令人为政策行为对塑料生命周期流量存量和温室气体排放的影响；最后，深入探究限塑令情景策略对塑料全生命周期系统减废降碳的协同效应，从而对其生命周期系统进行科学地优化协同管理，为塑料行业实现减废降碳的协同目标提供政策建议，这对我国实现“无废城市”和“碳达峰与碳中和”等战略目标具有重要的理论和现实意义。本文主要研究内容与结论如下：

（1）基于动态物质流分析方法建立我国使用最广泛的聚乙烯（PE）、聚丙烯（PP）和聚对苯二甲酸乙二醇脂（PET）塑料的流量存量模型，剖析我国社会经济系统2001-2020年塑料流量存量的动态演变规律。研究表明，PE薄膜、PE板片管型材（STP&C）、PP编制品（WG）、PP STP&C、纤维级PET是PE、PP和PET加工制造阶段的主要初级产品。建筑行业PE和PP的使用存量最大，而纺织行业PET的使用存量最大。废物方面，PET废塑料量最多，其次是PE废塑料。PET废塑料主要来源于纺织和包装行业，而PE和PP废塑料主要来自包装和农业。废塑料的未妥善处理占比已超过其焚烧占比。从2001年到2020年，包装与农业部门的PE废塑料在第一个时期（“十五”规划）增长最快，年均增长率高达65%和80%。另外，包装、电子和农业部门的PP废塑料也在第一个时期增长最快。与PE、PP不同，纺织行业的PET废弃物增长最快。第一个时期之后，我国加大了塑料废物处理力度，第二个时期（“十一五”规划）开始塑料废物量已经逐渐降低。从时间序列来看，不同规划时期的政策手段对塑料生命周期的流量存量具有重要的影响。

（2）将动态物质流分析模型和基于过程的生命周期评价模型相结合，构建了我国PET、PE和PP塑料全生命周期温室气体排放核算模型，基于该模型识别了温室气体排放的主要来源以及关键减排路径，并针对减少温室气体排放提出了对应措施。研究表明PET和PP塑料生产阶段的温室气体排放量分别占总排放量的75%和57%，生产阶段是这两种塑料生命周期温室气体排放的主要来源，而加工制造阶段是PE塑料全生命周期温室气体排放的关键过程。加工制造阶段，PET纤维的制造过程对温室气体排放有主要贡献，而PE薄膜、PE STP&C和PP WG的制造过程是PE与PP塑料加工制造阶段温室气体的主要来源。减少饮料服务中常用的一次性塑料（如PET瓶）和一次PET、PE和PP塑料膜包装，有助于生产和加工制造阶段的减排。在废物管理与循环阶段，三种废塑料的焚烧过程对温室气体的贡献最大。与焚烧相比，回收利用更有利于温室气体减排，但需要政府补贴等政策降低回收成本。

（3）基于PET、PE和PP塑料物质流分析模型，进一步探究了在未来限塑令情景策略下塑料的流量存量特征和减废效益，并提出了实现减废目标的相关政策建议。研究表明，如果不采取任何措施对塑料废物进行管控，那么塑料废物将会大幅增长，2030年的废物量将比2017年增长116%。总体来看，多措施综合策略的减废效益最显著，该策略下PET、PE和PP废塑料分别比基准情景（BAU）降低59%、56%和73%。单一策略中，生物基替代策略对减废的贡献最大，PET、PE和PP废塑料分别比BAU降低41%、37%和61%。禁止生产策略的减废效益仅次于生物基替代策略，但该策略下PE塑料的减废效益仍然显著。规范废物管理策略下，包装、农业和汽车行业的减废效益最为显著。采取多措施综合策略，特别是生物基塑料替代策略和禁止塑料生产策略相结合，将有助于实现减废目标。限塑令的持续实施将为减少PE、PP和PET废塑料做出更多贡献。

（4）基于塑料全生命周期温室气体排放核算模型以及限塑令情景分析，进一步探究限塑令各情景策略对塑料全生命周期系统温室气体排放的影响，并比较分析各情景策略对塑料生命周期系统的减排效益。与BAU相比，PE和PP塑料禁止塑料生产策略下具有显著减排效益，分别比BAU降低64%和18%。大部分玉米基与甘蔗基替代策略的减排效益并不理想。甘蔗基塑料比玉米基塑料具有更大的减排潜力，甘蔗基聚乳酸（PLA）和聚羟基烷酸酯（PHA）替代PET塑料使得其生命周期温室气体分别减排49%和21%。此外，提高回收率策略的减排效益显著而减少废物产生率策略的减排效益并不理想。多种措施组合策略下PET、PE和PP生命周期实现了温室气体减排。采取更严格的禁止生产策略、在废物管理与循环阶段使用低碳能源、以及多种措施相结合将有助于塑料生命周期实现温室气体减排。

（5）在限塑令背景下塑料物质代谢与温室气体排放情景分析的基础上，进一步探讨了限塑令各情景策略对塑料全生命周期系统减废降碳的协同效益，为塑料行业实现减废降碳的协同目标提供政策建议。研究表明，对于PE塑料，禁止生产策略不仅具有最高的减排效益（比BAU降低64%）还有很高的减废效益（降低33%），该情景策略是PE全生命周期实现减废降碳的协同策略。当甘蔗基PLA替代PP、甘蔗基PLA替代PET和甘蔗基PHA替代PET时，塑料全生命周期实现了减废降碳，其他生物基替代策略并不是减废降碳的协同策略。多措施综合策略下PET、PE和PP生命周期不仅温室气体排放量显著减少，且废物量也明显降低，该策略是三种塑料全生命周期实现减废降碳的协同策略。

Plastic pollution has caused a serious impact on the ecosystem and human health. China is one of the countries with the largest plastic yield, consumption, and waste in the world, and the annual waste plastic volume is about 30 million tons. The plastics industry is the basic industry for the development of the national economy and is also a high carbon emission industry. Greenhouse gases (GHG) are emitted in the plastics life cycle. In addition, China has issued a plastic limit order, which has had an important impact on the development of the plastics industry. However, the mechanism and key path of waste and carbon reduction in the life cycle of plastics under plastic restriction order and carbon neutrality are unknown. The plastic life cycle system often involves many factors such as society, economy, resources, and environment, which brings obvious complexity and uncertainty to the collaborative management of waste and carbon reduction of the plastic system. Therefore, the material flow analysis (MFA), life cycle assessment, scenario analysis, and Monte Carlo simulation are comprehensively adopted in this paper. First, the MFA and GHG emissions accounting model of the plastic life cycle are constructed to reveal the dynamic evolution of flows, stocks, and GHG emissions. Secondly, we further analyze the impact of the policy behavior of plastic restriction on flows, stocks, GHG emissions, and carbon peak in the plastic life cycle. Finally, the synergistic effect of the plastic restriction order strategy on waste and carbon reduction is discussed, and the synergistic strategy of waste and carbon reduction is identified to achieve the collaborative management of the plastic life cycle system, which has important theoretical and practical significance for China to achieve the strategic objectives of "waste free city" and "carbon peak and carbon neutrality". The main research contents and conclusions are as follows:
(1) The flows and stocks model of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) plastics, which are most widely used plastics in China, was established based on the dynamic MFA. The dynamic evolution of plastic flows and stocks in the socio-economic system from 2001 to 2020 was analyzed, and the uncertainty analysis of flows and stocks is carried out. The research shows that PE film, PE sheet, pipe, and profile (STP&C), PP fabric (WG), PP STP&C, and fiber grade PET are the main primary products in the manufacturing stage. The in-use stock of PE and PP in the construction industry is the largest, while the in-use stock of PET in the textile industry is the largest. In terms of plastic waste, the amount of PET waste is the largest, followed by PE waste. PET waste mainly comes from textile and packaging, while PE and PP waste mainly come from packaging and agriculture. The proportion of waste plastics not properly treated has exceeded that of incineration. From 2001 to 2020, the PE waste from the packaging and agricultural sectors grew fastest in the first period, with an average annual growth rate of 65% and 80%. In addition, PP waste from packaging, electronics, and agriculture also grew fastest in the first period. Different from PE and PP, PET waste from the textile industry grew fastest in the first period. After the first period, China increased its efforts to deal with plastic waste. Since the second period, the amount of plastic waste has gradually decreased. From the perspective of time series, the policy instruments in different planning periods have an important impact on the flows, stocks, and waste of plastic life cycle.
(2) Combining the dynamic MFA model with the life cycle assessment model, a GHG emissions accounting model for PET, PE, and PP plastics in the life cycle was created. Based on the model, the key processes and key emission reduction paths of GHG emissions of these three plastics were identified, and corresponding measures were proposed to reduce the GHG emissions. It is found that the production stage has the greatest carbon neutralization potential in the life cycle of PET and PP plastics. The manufacturing stage is the main source of GHG emissions in the life cycle of PE plastics. In the manufacturing stage, the manufacturing process of PET fiber has a significant contribution to GHG emissions, and the manufacturing process of PP film, STP&C, and PP WG is the main source of GHG in this stage. Reducing the use of disposable plastics (PET bottles) and disposable PET, PE and PP plastics film commonly used in beverage services will help reduce GHG emissions during the production and processing stage. In the waste management and recycling stage, the incineration process of three plastics contributes the most to GHG. Although recycling is more conducive to emission reduction, the GHG generated by recycling in China cannot be ignored. Government subsidies and other policies are needed to reduce recycling costs. Measures such as using low-carbon energy, improving recovery efficiency, and reducing tedious recycling processes are also needed.
(3) Based on the flow model and framework of PET, PE, and PP plastics and the scenarios of plastic restriction order, this paper explores the flow characteristics and waste reduction benefits of PET, PE, and PP plastics under various scenarios, and puts forward relevant policy recommendations and strategies to achieve the goal of waste reduction. Research shows that if no measures are taken to control plastic waste, which will increase significantly, and will increase by 116% in 2030 compared with 2017. In general, the waste reduction benefit of the multi-measure strategy is the most significant. Under the strategy, PET, PE, and PP waste are reduced by 59%, 56%, and 73% respectively compared with the baseline scenario (BAU). Among the single strategies, the bio-based alternative strategy has the largest contribution to waste reduction, with PET, PE, and PP waste reduced by 41%, 37%, and 61% respectively. The waste reduction benefit of the production ban strategy is only inferior to the bio-based alternative strategy, but the waste reduction benefit of PP plastics under this strategy is still considerable (33% less than BAU). Under the standardizing waste management strategies, the packaging, agriculture, and automobile industries have the most obvious waste reduction benefits. The multiple measures strategies, especially the strategy of replacement and banning plastics, will help to achieve waste reduction. The continuous implementation of the plastic restriction order will make more contributions to the reduction of PE, PP, and PET waste.
(4) Based on the dynamic MFA and GHG emission accounting model and the plastic restriction order strategy, the GHG emissions and carbon peak of PET, PE, and PP plastics under the plastic restriction order were analyzed. Finally, we provide relevant policy suggestions and strategies for PET, PE, and PP to achieve the goal of the carbon peak in the life cycle. Compared with the BAU, PE and PP plastics have significant emission reduction benefits under the prohibition strategy, which are 64% and 18% lower than BAU respectively. The emission reduction benefits of most corn-based and sugarcane-based alternative strategies are not ideal. Sugarcane-based plastics have greater emission reduction potential than corn-based plastics. Sugarcane-based PLA and PHA replace PET plastics to reduce GHG emissions by 49% and 21% respectively. In addition, the emission reduction benefit of increasing recovery rate is significant, while the emission reduction benefit of reducing waste generation rate is not ideal. In the waste treatment process, especially in recycling, it is very important to use low-carbon processes. PET, PE, and PP by multiple measures have achieved GHG emission reduction. The adoption of a stricter production ban strategy and the use of low-carbon energy in the waste management and recycling stage will help achieve carbon emission reduction through the combination of various measures.
(5) Based on the analysis of plastic metabolism and GHG emissions under the plastic restriction order, we further analyze the waste and emission reduction benefits generated by each scenario strategy and discuss the synergistic benefits of these strategies on waste and carbon reduction, to provide policy optimization basis for realizing the synergistic goal of waste and carbon reduction for plastics. The research shows that for PE plastics, the production ban strategy not only has the highest emission reduction benefit (64% lower than BAU) but also has a good waste reduction benefit (33% lower). The strategy is a collaborative strategy to achieve waste and carbon reduction throughout the life cycle of PE. When sugarcane-based PLA replaces PP, sugarcane-based PLA and PHA replace PET, it not only makes PP and PET plastics have good carbon reduction benefits but also has high waste reduction benefits. Under the strategy of multiple measures, the life cycle of PET, PE, and PP not only significantly reduced GHG emissions, but also significantly reduced waste. In general, the multiple strategy is a collaborative strategy for three plastics to achieve waste and carbon reduction throughout their life cycle.