A circular (bio)economy is sustained through use of secondary raw material and biomass feedstock. In life cycle assessment (LCA), the approach applied to address the impact of these feedstocks is often unclear, in respect to both handling of the recycled content and End-of-Life recyclability and disposal. Further, the modelling approach adopted to account for land use change (LUC) and biogenic C effects is crucial to defining the impact of biobased commodities on global warming. We depart from state-of-the-art approaches proposed in literature and apply them to the case of non-biodegradable plastic products manufactured from alternative feedstock, focusing on selected polymers that can be made entirely from secondary raw material or biomass. We focus on global warming and the differences incurred by recycled content, recyclability, LUC, and carbon dynamics (effects of delayed emission of fossil C and temporary storage of biogenic C). To address the recycled content and recyclability, three formulas recently proposed are compared and discussed. Temporary storage of biogenic C is handled applying methods for dynamic accounting. LUC impacts are addressed by applying and comparing a biophysical, global equilibrium and a normative-based approach. These methods are applied to two case studies (rigid plastic for packaging and automotive applications) involving eight polymers. Drawing upon the results, secondary raw material is the feedstock with the lowest global warming impact overall. The results for biobased polymers, while promising in some cases (polybutylene succinate), are significantly affected by the formulas proposed to handle the recycled content and recyclability. We observe that some of the proposed formulas in their current form do not fully capture the effects associated with the biogenic nature of the material when this undergoes recycling and substitutes fossil materials. Furthermore, the way in which the recycled content is modelled is important for wastes already in-use. LUC factors derived with models providing a combined direct and indirect impact contribute with 15–30% of the overall life cycle impact, which in magnitude is comparable to the savings from temporary storage of biogenic C, when included. End-of-Life formulas can be improved by addition of corrective terms accounting for the relative difference in disposal impacts between the recycled and market-substituted product. This affects the assessment of biobased materials. Inclusion of LUCs effects using economic/biophysical models in addition to (direct) LUC already embedded in commercial datasets may result in double-counting and should be done carefully. Dynamic assessment allows for detailed modelling of the carbon cycle, providing useful insights into the impact associated with biogenic C storage.

中文翻译：

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来自生物质和回收原料的塑料的碳足迹：方法论见解

循环（生物）经济是通过使用二次原材料和生物质原料来维持的。在生命周期评估 (LCA) 中，用于解决这些原料影响的方法在回收内容的处理以及生命周期结束的可回收性和处置方面通常并不明确。此外，用于解释土地利用变化 (LUC) 和生物碳效应的建模方法对于定义生物基商品对全球变暖的影响至关重要。我们脱离了文献中提出的最先进的方法，并将它们应用于由替代原料制造的不可生物降解塑料产品的情况，重点关注可以完全由二次原材料或生物质制成的选定聚合物。我们关注全球变暖以及回收内容、可回收性、LUC、和碳动力学（化石碳的延迟排放和生物碳的临时储存的影响）。为了解决回收内容和可回收性，比较和讨论了最近提出的三个公式。使用动态核算方法处理生物碳的临时储存。通过应用和比较生物物理、全球平衡和基于规范的方法来解决 LUC 影响。这些方法应用于涉及八种聚合物的两个案例研究（用于包装和汽车应用的刚性塑料）。根据结果​​，二次原料是总体上对全球变暖影响最小的原料。生物基聚合物的结果虽然在某些情况下很有希望（聚丁二酸丁二醇酯），但受到建议用于处理回收内容和可回收性的配方的显着影响。我们观察到，当材料经过回收和替代化石材料时，目前形式的一些拟议公式并没有完全捕捉到与材料的生物性质相关的影响。此外，对回收内容建模的方式对于已经在使用的废物很重要。通过提供直接和间接影响的模型得出的 LUC 因子占整个生命周期影响的 15-30%，其规模与临时储存生物碳（如果包括在内）的节省相当。可以通过添加修正条款来改进报废公式，以说明回收和市场替代产品之间处置影响的相对差异。这会影响生物基材料的评估。除了已经嵌入商业数据集中的（直接）LUC 之外，使用经济/生物物理模型包含 LUC 效应可能会导致重复计算，应谨慎进行。动态评估允许对碳循环进行详细建模，为与生物碳储存相关的影响提供有用的见解。