Characteristics and Material Flows of Non-Packaging Plastics in Municipal Solid Waste: A Case Study from Vienna

Abstract

In contrast to packaging, non-packaging plastics remain largely untargeted by EU regulations, despite their comprising over 60% of primary plastics in the EU 27 + 3 in 2022. This results in lower separate collection and recycling rates as well as fewer studies analysing recycling-relevant characteristics in non-packaging plastic waste (NPW), which are relevant to ensure the circularity and sustainable management of all plastics. This study presents a detailed characterisation of NPW found in mixed municipal solid waste and lightweight packaging waste on polymer and product levels, using the case study of Vienna, Austria. Results show that 4100 t/yr of polymers targeted for recycling, especially polypropylene, are currently discarded and lost in mixed MSW. A large share of NPW, however, exhibits recycling-hindering traits like multi-polymer objects or black colouring. While products made of high-quality food contact material were assessed to be ideal for separate collection to ensure closed-loop recycling, consideration should be given to collecting the majority of NPW via recycling centres to prevent contamination of target polymers with currently non-targeted other polymers. Design for recycling guidelines should also be introduced for non-packaging plastics, targeting separability, colouring and small-scale products. By doing so, a more sustainable management of NPW can be achieved.

1. Introduction

Global plastic use is predicted to increase significantly, with studies forecasting a doubling of plastics consumed by 2050 [1] or even tripling by 2060 [2]. This development is driven by the numerous applications for plastics [3] as well as population and economic growth in lower-income countries [2]. At the same time, plastic accumulation in aquatic environments is anticipated to triple, resulting in environmental degradation and potential hazards to human health, society, and economy, highlighting the need for enhanced circularity and sustainable management of plastics [2,4,5].

Plastics are a favoured working material due to their versatility, offering a wide array of polymer types and customization options [6]. In 2022, plastic converters in the EU 27 + 3 utilised 54 Mt of primary plastics, of which 61% (30.5 Mt) were used for non-packaging plastic applications [3,7]. These comprise multiple areas, including building and construction, electronics, and household products. Lifespans of non-packaging plastics vary significantly, ranging from under five years in agriculture to around 50 years in building and construction, specifically for plastic pipes [8]. Consequently, these products are engineered by prioritising durability, resulting in the utilisation of complex, multi-polymer, and additive-rich plastics [9,10]. Whilst polyolefins (e.g., polypropylene (PP), polyethylene (PE)), and polyethylene terephthalate (PET) are primarily applied in the packaging sector, other polymers are predominantly utilised for non-packaging plastics, with 12.4 Mt making up around 42% of the entire non-packaging plastics-polymer demand in the EU in 2019 [9,11]. This polymer group includes engineering polymers such as acrylonitrile butadiene styrene (ABS) and polycarbonate (PC), which offer enhanced mechanical and thermal properties, thus replacing metal or glass components in the areas of transportation, electronics, and building and construction [9,12,13].

While packaging waste is produced and discarded within a similar time frame, the longer lifespan of non-packaging plastics results in a delayed emergence of waste. In 2022, non-packaging plastics waste (NPW) accounted for 43% (13.8 Mt) of post-consumer plastic waste in the EU 27 + 3 [12]. The remaining plastics contribute to Europe’s growing plastic stock, increasing by 8–10 Mt/yr [8]. Around 56% of NPW in the EU 27 + 3 undergoes thermal recovery, 32% is landfilled, and merely 12% recycled [12]. Whilst regulatory measures to increase plastic waste recycling have been implemented in order to establish a circular economy in the EU [14,15], the primary focus remains on plastic packaging waste (PPW), with established targets prescribing recycling and collection rates, mandatory content of recycled plastics, and the recyclability or reusability of packaging by 2030 [16,17]. In contrast, NPW is typically addressed within the broader context of municipal waste recycling targets in the Waste Framework Directive [18], with certain areas (e.g., building and construction, transportation, electronics) being targeted through the Circular Economy Action Plan [15,19,20,21].

Mechanical recycling is the primary treatment method for post-consumer plastic waste in the EU [12], involving sorting, shredding, washing and regranulation. The immiscibility of different polymers when melted [22] leads to the separation of plastic waste by polymer type to enhance the quality of the recycled plastic material. Various sorting technologies are employed, with near-infrared (NIR) sensors being the most widely used [6,22,23]. The choice of target polymers depends on factors such as market demand, price and input material purity [24,25]. Commonly targeted polymers in European sorting and recycling plants include PET, high-density and low-density polyethylene (HDPE, LDPE), PP, and polystyrene (PS) [24,26].

Recycling efficiency, recovery yield and the quality of recycled plastic material depend on several factors [27,28]: Dark or black coloured plastics escape NIR detection [29,30], impurities (non-plastic parts), non-targeted and multiple-polymer objects negatively influence sorting and recycling [23,31], and certain additives such as flame retardants hinder recycling processes and contaminate recycled plastic material [25,32]. While a comprehensive understanding of plastic waste composition, particularly of post-consumer plastic waste and the NPW contained therein is crucial to enhance the recycling of this highly complex waste stream, the availability of detailed data remains limited [9,23,33,34]. This can be attributed to the aforementioned legislative focus on packaging waste as well as the heterogeneous areas of application and lifespans, leading to inconsistent collecting and monitoring of NPW in the EU [35].

A number of studies have modelled plastic flows for the EU, including Amadei et al. [36] and Hsu et al. [37], who has identified between 400 plastic and plastic-containing products. Eriksen et al. [38] focused on European PET, PP, and PE flows. However, only a few studies have analysed NPW in post-consumer plastic waste at country level. Eriksen and Astrup [33] characterised separately collected plastic waste from Copenhagen, including NPW, based on product type, colour, and polymer composition, followed by extrusion and pelletisation tests [39]. The most detailed analysis was performed by Faraca and Astrup [31] with plastic waste from Danish recycling centres, assessing product types, polymer composition, colour, presence of impurities, and recycling potential. Outside of Denmark, Jacobsen et al. [40] analysed factors influencing separate rigid plastic waste collection in Flanders, Belgium, while Van Eygen et al. [41] quantified plastic flows, including NPW, for Austria. The latter authors, however, did not analyse the plastic flows regarding recycling-relevant properties.

However, a review of some of the most recent studies on plastics in the EU illustrates knowledge gaps regarding quantities and qualities of NPW. This counts particularly for mixed MSW, and a more sustainable management of the therein contained NPWs requires a better understanding of their contents and main characteristics. This study therefore aims to fill some of the research gaps mentioned by providing comprehensive data on NPW, particularly rigids, in mixed MSW and separately collected lightweight packaging waste (LPW), where NPW is currently classified as a misplacement (see Section 3.2). The focus is put on a detailed characterisation of NPW on product level while also conducting a systematic polymer-analysis using Fourier Transform Infrared (FTIR) spectroscopy.

For this case study, Vienna, the capital city of Austria, was chosen. Firstly, Austria achieved the second highest recycling rate of municipal solid waste in the EU in 2022, with 62.6% [42]. Vienna is not only of relative importance in Austria in terms of population and waste generation; the city also possesses a well-established and advanced waste management system [43] while providing access to relevant waste data for the year 2022. Insights from this case study are therefore relevant for both Austria and other EU member states. To this end, the following research questions (RQ) are investigated: (RQ1) How can NPW from mixed MSW and LPW collection from Vienna be characterised based on area of application and product type? (RQ2) Which polymer composition can be observed for NPW in these waste streams? (RQ3) What are the material flows of NPW in Vienna? (RQ4) What proportion of NPW shows characteristics that hinder their recycling (e.g., multi-polymer objects, metals, colouring)?

2. Materials and Methods

2.1. Material Flows of NPW in Vienna

2.1.1. Scope

Vienna, the capital of Austria with a population of 1.93 million citizens at the time of analysis, was used as a case study. Accounting for approximately 22% of Austria’s population [44] and a fifth of Austria’s generated MSW [45], the city plays a crucial role in achieving plastic recycling targets in the country.

The subject of this study is rigid NPW in mixed MSW and LPW. In the literature, rigid or hard plastics frequently include packaging waste [33,40,46,47], which lies beyond the scope of this study. Additionally, non-packaging foils are excluded from the analysis. The characterisation of foils according to product type and polymer has already been carried out, for example, by Faraca and Astrup [31] for Denmark and Rainer et al. [48] for Vienna, with the latter also analysing colour and print. Both studies also found that the content of foils is much lower in NPW than in PPW. Furthermore, Horodytska et al. [49] have outlined the challenges associated with plastic foil recycling, with post-consumer foils proving to be particularly difficult to recycle due to contamination and degradation. Although recycling is technically possible, it is often not economically feasible despite the identification of environmental benefits [26,50].

Mixed MSW in Vienna (0.56 Mt in 2022) [45] is collected by the department for municipal waste management, known as Magistratsabteilung 48 (MA 48). LPW has been separately collected in Vienna since 1993, with frequent changes in targeted packaging fractions. Currently, LPW collection distinguishes between container collection from collection points for households and other waste producers in densely populated areas and yellow bag collection from households in less-densely populated areas. MA 48 is commissioned to carry out this collection by Altstoff Recycling Austria AG (ARA), which is the largest company in Austria responsible for the management and recycling of packaging waste under the extended producer responsibility (EPR) scheme of packaging waste producers [43]. Thus, the costs for collection, sorting, and recycling are covered by producers [51]. Contrary to separately collected wastepaper, where packaging and non-packaging are commingled, NPW is not collected in LPW containers and bags since collection is not covered by the aforementioned EPR scheme. However, rigid plastic waste can be disposed of in different fractions in Viennese recycling centres, including CDs (6 t in 2022), PET plastic waste (267 t in 2022) and, since 2018 [52], specifically rigid plastics (e.g., garden chairs, oversized packaging) (1101 t in 2022) [53]. Small NPW items (toys, coat-hangers, toothbrushes, ballpoint pens) are, in contrast, visually promoted on the mixed MSW containers [54].

2.1.2. Material Flow Analysis of NPW

Material flow analysis (MFA) is a tool used in the field of waste management to describe waste flows and changes in stock within a specific time frame and geographic area. As outlined by Brunner and Rechberger [55], flows and stocks are balanced on the principle of mass conservation (Equation (1)), with k_I representing the number of input flows and k_O the number of output flows

$$\sum _{k_I}{\dot{m}}_{input}=\sum _{k_O}{\dot{m}}_{output}+{\dot{m}}_{stock}$$

(1)

A particular waste flow can be described as a good, which in turn comprises subgoods, representing different types of waste that are components of the waste flow. To calculate the material flow of a subgood j in a good i according to Equation (2), it is necessary to determine its content $c_{ij}$ in the related good ${\dot{m}}_i$.

$${\dot{m}}_{ij}={\dot{m}}_i\mathsf{\bullet }{c}_{ij}$$

(2)

In the present study, goods comprise municipal solid waste flows containing substantial amounts of NPW, i.e., mixed MSW and LPW. The subgood in this study encompasses rigid NPW that is contained in the aforementioned goods, with annual quantities being calculated according to Equation (2). In the present study, the material flows of the subgood NPW ${\dot{m}}_{ij}$ is further distinguished into sub-subgoods k according to the fractions of interest in this study. For the calculation of the material flows of sub-subgoods, the material of the subgood NPW ${\dot{m}}_{ij}$ is multiplied by the content of each sub-subgood fraction $c_{ijk}$, as shown in Equation (3).

$${\dot{m}}_{ijk}={\dot{m}}_{ij}\mathsf{\bullet }{c}_{ijk}$$

(3)

The annual waste flows of goods for mixed MSW and LPW and the content of the subgood NPW in these waste flows were provided by MA 48 for the year 2022. The content of each sub-subgood fraction $c_{ijk}$ was determined by sampling and characterisation of the subgood NPW samples as described in the next Section 2.2.

It should be noted that the MFA conducted does not consider material losses due to collection or transportation. Furthermore, the extrapolation of masses per year is subject to certain assumptions regarding polymer composition, colouring, and presence of impurities, as is stated in detail in the respective Section 3.3 and Section 3.4.

2.2. Sampling and Characterisation of NPW

2.2.1. Waste Sampling and Pre-Sorting

A comprehensive MSW sampling campaign was carried out by MA 48 in October 2022. The sampled waste flows comprised, amongst others, mixed MSW and separately collected LPW, consisting of container and bag collection. Sampling and sorting were carried out by an engineering company in accordance with a standardised technical guideline [56], which considers both national standards [57] and European specifications [58], as described more in detail by Gritsch et al. [59]. A pre-determined sorting catalogue was utilised to sort each waste flow into fractions. In both waste streams analysed, the engineering company used the national Packaging Ordinance [60] to distinguish between packaging and non-packaging waste. For this study, NPW samples from the aforementioned waste streams were further analysed (see Section 2.2.2) because NPW was explicitly classified as a fraction of interest in those waste streams, with both containing significant shares of NPW [61].

During the three-week sampling period carried out from the 10 to 31 October, a total of 3600 kg of mixed MSW samples were obtained. The samples were drawn on a daily basis during the work week, thereby capturing daily variations in waste constitution. Each day, 20 different addresses were randomly selected throughout Vienna, from where samples (240 L of mixed MSW) were drawn directly from the containers. This ensured a representative reflection of the entire city’s waste composition due to a total of 300 sampled addresses from strata of different settlement structures and varied purchasing power. A manual analysis ensued on the same day, during which the MSW samples were sorted into a total of 174 fractions, with rigid NPW being one of them. This rigid NPW fraction from mixed MSW was obtained within two of the three sampling weeks, totalling 29 kg. The sampling of LPW was conducted through the extraction of approximately 1400 kg (1300 kg from container and 100 kg from bag collection) from 12 randomly selected collection vehicles that each follow different collection routes, also ensuring the representative constitution of Viennese LPW. The samples were obtained through a wheel loader shovel and further divided by the engineering company into 65 fractions, including rigid NPW as one fraction. This NPW fraction was obtained from the separate LPW collection, totalling 32 kg from the container and 5 kg from bag collection. The latter exclusively targets single-family households in designated districts of Vienna [62], with a yearly yield of merely 300 t, in comparison to approximately 11,000 t/yr of collected LPW in containers [61]. Because of these low mass flows of the bag collection, the results of the two collection variants were combined as LPW in the results of this study.

2.2.2. Conducted Characterisation of NPW

The entirety of the sampled subgood of rigid NPW from both waste streams considered were further analysed, resulting in sub-subgoods that describe the characteristics and quality of NPW. Each object was assigned a number, weighed, and characterised according to: (i) area of application and product type, (ii) polymer, (iii) colour, and (iv) presence of impurities. The NPW samples consisted of 1582 NPW objects in mixed MSW and 823 in LPW. No additional drying steps were performed on these samples, as the water content determination during the sampling campaign all resulted in a water content of 0 w% [61]. The allocation of each rigid NPW to its respective area of application and product type (sub-levels) was conducted through visual analysis. A range of classifications of NPW can be found in the literature, with varying levels of complexity [12,31,37]. In order to ensure comparability with Austrian plastic flows, terms for areas of application and product types were adopted and extended from Van Eygen et al. [41], who analysed the plastic flows in Austria for the year 2010.

In total, eight areas of application were distinguished, namely Building and Construction, Transport, Electronics, Furniture, Agriculture and Gardening, Medicine, Household, and Others. Within these areas, 17 product types were identified at sub-level 1 and 38 product types at sub-level 2 (see Table S1 in the Supplementary File). At this stage, smaller NPW measuring less than 5 cm, was determined via measuring tape, weighed, and excluded from further characterisation as it is assumed that NPW of this size is sieved out in Austrian plastic sorting plants and incinerated, thus not being recoverable for recycling [63]. Additionally, used medical equipment such as syringes was not further analysed due to considerations of hygiene and safety. Via visual assessment, the primary colour of each NPW was distinguished according to following shades: clear/transparent, white, black, grey, red, orange, yellow, green, blue, purple, pink, brown, and metallic. Furthermore, it was noted whether multiple colours were present on an object. The presence of metals and non-plastic parts was also assessed, but no separation was conducted in this study.

To determine the polymer of each NPW, it was initially attempted to locate a Resin Identification Code (RIC). In the absence of a code, FTIR spectroscopy was conducted utilising the Agilent Series 4300 Handheld FTIR Spectrometer (Agilent Technologies, Inc., Santa Clara, CA, USA). A measurement was deemed successful when a match of more than 70% with the database was reached. This threshold is based upon the “Technical Subgroup on Marine Litter” and is used as a minimum matching value for the FTIR-analysis of microplastics [64] (for further information regarding FTIR-data, see Supplementary File). Given the tendency of NPW to include multi-polymer objects, the visually predominant polymer was identified, with the presence of additional polymers also being recorded. Samples in which a RIC was present were not further analysed with FTIR, as it was assumed that the given polymer matched the code. Figure 1 presents a schematic overview of the goods, subgoods, and sub-subgoods of this study as well as analysed characteristics.

2.2.3. Presentation of Results

The results are presented as the distinguished NPW categories in w% of the total NPW amount in each of the two waste streams. For the categories (i) Area of application + Product type, and (ii) Polymer, the annual material flows at sub-subgood level in t/yr are provided.

3. Results and Discussion

3.1. Material Flows of Goods and Subgoods

Extrapolated to Vienna by MFA, a total amount of 9441 t of rigid NPW was accumulated in Viennese mixed MSW (1.9 w% of totally generated mixed MSW in Vienna) and 297 t in LPW (2.7 w% of separately collected LPW in Vienna) in the year 2022 with no significant changes in quantity observed over the regularly conducted MSW sampling campaigns of Vienna [65,66].

3.2. Areas of Application and Product Types of NPW in Vienna

In Figure 2a, the respective areas of application for NPW found in mixed MSW and LPW are presented. In both waste streams, NPW was primarily assigned to the areas of Household and Others (51 w% in mixed MSW, 73 w% in LPW). Except for Medicine, waste from the remaining areas is collected in Austrian recycling centres. Alternatively, products such as electronic devices and end-of-life vehicles can be returned to the retailer at the end of their life cycle [45]. This explains the larger share of the two aforementioned areas of application in this study. Furthermore, the expected lifetime for NPW from Household and Others, at 0–12 years, is additionally lower than that of other non-packaging areas [3,8], resulting in a more frequent waste generation.

The proportion of NPW measuring less than 5 cm as well as the non-analysed fraction was three times larger in the mixed MSW sample than in the LPW sample. This discrepancy can be partly attributed to further non-analysed Medical equipment in the mixed MSW sample. The sole share of NPW < 5 cm amounts to 3.6 w% in mixed MSW in comparison to 1.2 w% in LPW. Additionally, several studies have demonstrated in the case of packaging waste, for which more data is available, that smaller packaging has a lower probability of being separately collected [59,67,68,69]. This may also apply for NPW.

A closer investigation of the area Household (Figure 2b) reveals that of all samples 76 w% of Kitchen-use products, including kitchen utensils and beverage bottles, were present in the LPW collection. Furthermore, this product type constitutes 20 w% of samples in LPW, in comparison to 8 w% in mixed MSW. In contrast, 76 w% of Household cleaning items such as sponges or brooms originated from mixed MSW. These findings suggest that if consumers decide to dispose of NPW in the LPW, despite them not being actively advertised for separate collection (so-called “intelligent misplacements” according to Bünemann et al. [70]), they are more likely to separately collect NPW that is similar to already advertised packaging waste (e.g., beverage bottles). Utilising NPW for cleaning purposes (e.g., sponges), however, may lead consumers to perceive these products as “dirty”, leading to their disposal in mixed MSW instead. The area Household also comprises Miscellaneous products, including coat-hangers, buckets, and baskets. The latter were found in 64% of cases in mixed MSW. This could be explained due to the limiting design of Viennese LPW collection containers, consisting of two small circular openings. These are supposed to promote the collection of plastic bottles and reduce the proportion of misplacements in LPW, therefore hindering the disposal of bulky plastics [71].

The area Others can be characterised by a high degree of diversity [9], as is further supported by Hsu et al. [37], who distinguished eight product types with 117 different plastic containing products. In the present study, the category Others was divided into five product types at sub-level 1. The sub-level 1 category Leisure included toys or analogue media, whereby the high proportion of items measuring less than 5 cm in mixed MSW can be attributed to small toys. Office supplies and Body cleansing and personal care items were predominantly found in mixed MSW. This observation could be attributed to a lack of containers for separate collection in bathrooms and office rooms within households as well as lack of awareness for the collection of certain product types (e.g., cosmetics) [72].

Non-assignable product types made up 44 w% of the area Others in mixed MSW and 71 w% in LPW, consisting in large parts of fragmented or unknown NPW, where a reconstruction of the originally intended use was not possible. A possible reason for the high share of non-assignable products observed in LPW is presented in Section 3.4. Further details regarding sub-level 1 and 2, along with their sample distribution between mixed MSW and LPW, can be found in Tables S2–S5 of the Supplementary File.

3.3. Polymer Composition and Material Flows of NPW in Vienna

The following results assume that analysed NPW consists of mono-polymer objects. For data regarding multi-polymer objects and impurities, see Section 3.4.

The results of the FTIR-spectroscopy conducted and the polymer identification through RIC are illustrated in Figure 3a. Details regarding the proportion of NPW identified via FTIR versus RIC are provided in the Supplementary File. It should be noted, however, that in up to 76 w% of samples, no RIC was detectable. NPW from both waste streams are predominantly composed of PP and other polymers, with only slight differences between the waste streams analysed. The present findings partially correlate with Faraca and Astrup [31], who identified PP as the most commonly found polymer among hard plastic waste, accounting for 48 w% (see

Table 1. Reported polymer shares of rigid NPW in w% across studies. * The results from Faraca and Astrup [31] include 40 w% to 65 w% packaging waste.

Polymer	References	Eriksen and Astrup [33]	Faraca and Astrup [31] *	Blasenbauer et al. [34]
	Sampled Waste Stream	Separately Collected Plastic Waste from Households (Copenhagen)	Plastic Waste from Danish Recycling Centres	Plastic Outputs from Austrian Material Recovery Facilities
PET		-	3%	1–2%
PE		11%	HDPE 22%	HDPE 19–30%
			LDPE 0.3%	LDPE 0–4%
PVC		-	8%	1–15%
PP		61%	48%	28–42%
PS		-	6%	6–11%
Other		27%	12%	10–26%

). However, it is important to recognise that around 40 w% to 65 w% of sampled hard plastic waste of Faraca and Astrup [31] consisted of food and non-food packaging. Blasenbauer et al. [34] specifically analysed the polymers of rigid non-packaging plastics from two Austrian material recovery facilities that treat mixed MSW. In their results, PP also exhibits the largest proportion, ranging from 28 w% and 42 w%. In contrast, other polymers have a lower share than in the present study, ranging from 10 w% to 26 w%. Furthermore, Blasenbauer et al. [34] identified a significantly higher percentage of HDPE in their samples, with up to 30 w%, while this constituted less than 1 w% of both waste streams in the present study. This could be due to the co-processing of bulky and commercial waste with mixed MSW in the material recovery facilities of that study, therefore including HDPE rich articles such as furniture or pipes [73]. In total, a significant proportion of NPW in both mixed MSW and LPW consist of target polymers for sorting and recycling facilities, specifically 48 w% of NPW in mixed MSW and 54 w% in LPW.

The allocation of the yearly amounts of NPW in mixed MSW and LPW to their respective areas of application is demonstrated in Figure 3b (see

Table A1. Content and amount of polymers in mixed MSW and LPW according to areas of application in w% and t/yr, on a dry matter basis. Data does not include share of <5 cm/not analysed.

Area of Application		1. Building and Construction		2. Transport		3. Electronics		4. Furniture		5. Agriculture and Gardening		6. Medicine		7. Household		8. Others
Polymer	Waste stream	w%	t/yr	w%	t/yr	w%	t/yr	w%	t/yr	w%	t/yr	w%	t/yr	w%	t/yr	w%	t/yr
PET	Mixed MSW	0%	0	0%	0	0%	0	0%	0	79.3%	69.4	0%	0	3.4%	3	17.2%	15.1
	LPW	0%	0	0%	0	12.9%	1.1	0%	0	0%	0	0%	0	64.1%	5.7	23%	2
HDPE	Mixed MSW	0%	0	0%	0	0%	0	0%	0	0%	0	0%	0	0%	0	100%	1
	LPW	0%	0	0%	0	0%	0	0%	0	0%	0	0%	0	51.1%	0.4	48.9%	0.4
PVC	Mixed MSW	56.4%	317.4	0%	0	0%	0	0%	0	0%	0	0%	0	0%	0	43.6%	245.2
	LPW	15.1%	2.1	0%	0	0%	0	0%	0	1%	0.1	0%	0	1.3%	0.2	82.5%	11.6
LDPE	Mixed MSW	5.6%	21.6	0%	0	0%	0	0%	0	21.6%	83.1	3.2%	12.4	0%	0	69.6%	267.7
	LPW	10.4%	0.7	0%	0	0%	0	0%	0	0%	0	0.3%	0	55.5%	3.9	33.8%	2.4
PP	Mixed MSW	12.9%	392.3	0%	0	0.1%	1.8	1.7%	50.2	3.1%	93.5	0%	0	55.6%	1686.3	26.7%	811.3
	LPW	0.2%	0.3	2.2%	2.7	0.3%	0.3	24.%	29.4	1%	1.2	0%	0	39.1%	46.5	32.4%	38.4
PS	Mixed MSW	13.9%	92.6	0%	0	2%	13.1	0%	0	0%	0	0%	0	8.7%	57.7	75.4%	500.6
	LPW	0%	0	2.2%	0.5	0.1%	0	0%	0	0%	0	0%	0	28.6%	6.5	69.1%	15.7
Other	Mixed MSW	21.9%	858.8	0.6%	22.4	6.3%	247.1	0%	0	0%	0	40%	1567.4	18.2%	713.1	12.9%	506.3
	LPW	8%	9.5	15.3%	18.1	3.5%	4.1	0%	0	3.1%	3.7	2.4%	2.8	12.6%	14.9	55.2%	65.6
Sum per area in t/yr	Mixed MSW	1682.7		22.4		262		50.2		246		1579.8		2460.1		2347.1
	LPW	12.7		21.3		5.6		29.4		5		2.9		78.1		136.1

in the Appendix A). The results do not include the fine fraction of <5 cm and non-analysed Medical equipment (approximately 791 t/yr in mixed MSW and 6 t/yr in LPW). Despite not being advertised for separate LPW collection, around 160 t/yr of NPW containing target polymers are currently co-collected with LPW and treated in sorting and recycling facilities. Conversely, more than 4100 t/yr of potential target polymers, particularly over 3000 t/yr of PP, are discarded in mixed MSW and subsequently incinerated [45]. If these amounts were instead separated and recycled, the Viennese recycling rate of municipal waste would increase by 0.54 percentage points. However, the presence of impurities further lowers the share of recyclable NPW, as stated in Section 3.4.

Approximately 56 w% of PP in mixed MSW is found in the area Household. The polymer composition on product type level (see Tables S10–S15 in the Supplementary File) shows that over 800 t/yr of PP can be traced back to buckets and baskets and over 500 t/yr originate from kitchen utensils such as spatulas or containers. In the area Others, more than 200 t/yr of PP can be found in the product type toys. Around 4400 t/yr of discarded NPW in mixed MSW, however, contain currently non-targeted polymers, primarily 3900 t/yr of other polymers. These various polymers are present in nearly all areas of application in both analysed waste streams. While the recycling of certain other polymers, e.g., the engineering polymers included therein, is technically feasible, the presence of additives in this polymer group and their variable properties hinder the generation of a high-quality recycled plastic material [74]. A listing of the around 50 identified other polymer types in the analysed samples can be found in the Supplementary File. PVC, on the other hand, is concentrated in mixed MSW in the area Building and Construction, specifically in the product types of pipes and tubes. Whilst mechanical recycling is practiced for PVC window-frames and pipes in Austria, older PVC waste has been found to contain toxic substances like lead, rendering recycling difficult [26,45,75]. This polymer is additionally unwanted as refuse-derived fuel (RDF) for the cement industry, as the high chlorine content leads to adhesions and packings in the combustion zone [75,76].

The studies by Faraca and Astrup [31] and Eriksen and Astrup [33] have assigned levels of quality (high, medium, low) to each area of application with regard to existing legislation, which restricts the use of certain amounts of chemicals in plastic items and therefore influences their potential to function as a virgin material substitute. These authors rate food packaging with the highest quality level, toys, pharmaceuticals and electronics as medium, and all remaining areas as low quality. For the present study, a high-quality level can be assumed for Kitchen-use products in the area Household due to the fact that most items found are in direct contact with food and must comply with EU regulations regarding food contact materials [77]. Based on this rating system, 8 w% (~740 t/yr) of NPW in mixed MSW was classified as high-quality, 9 w% (~850 t/yr) as medium quality, and the remaining 83 w% as low quality. In comparison, NPW in LPW contains twice the share of high-quality plastic items with 18 w% (~55 t/yr) due to the higher frequency of Kitchen-use products found in this waste stream (see Section 3.2). Additionally, 10 w% (~30 t/yr) of medium-quality items are identified. The results from Faraca and Astrup [31] regarding the quality of hard plastic waste from recycling centres show a comparable composition to that of NPW in LPW in this study, with 14 w% of high-quality, 13 w% of medium quality and 73 w% of low quality, while the share of low quality NPW from mixed MSW is 10 percentage points higher.

Regarding the previous results, the inclusion of selected NPW from the area “Household” into the separate LPW collection could be envisaged to increase recycling of NPW. The predominant share of PP and the high-quality level of Kitchen-use products could enable qualitative recycling and help to introduce closed-loop collection and recycling of food-contact materials [67], where only low percentages of non-food polymer inputs for recycling are tolerated [78,79]. The results have further shown an already existing tendency to dispose of the aforementioned product type via separate collection. While the inclusion of NPW into an EPR scheme would lower their share in mixed MSW, as proposed by Lubello et al. [80], it would also lead to the introduction of a large amount of so far non-targeted other polymers, potentially contaminating target polymers [81]. Due to the heterogeneity of products, clear advertisements for separate collection would be an additional challenge. The promotion of separate collection in recycling centres, as is already practiced in Vienna [52] or Denmark [31] could therefore be an alternative to prevent contamination of the current LPW stream while still enabling the recovery of target polymers or selected engineering polymers. Additionally, the promotion of design for recycling for all non-packaging plastics is recommended, as is further discussed in Section 3.5.

3.4. Colouring and Presence of Impurities in NPW in Vienna

The recyclability of a product is influenced by its polymer composition as well as the colouring of the plastic [25,30,82]. The listed results assume that analysed NPW was monochromatic. However, objects also tend to exhibit multiple colours. Further details are listed in Table S17 in the Supplementary File.

In Figure 4, the colour composition per waste stream and per polymer type and area of application is presented (see also

Table A2. Colour composition of NPP in mixed MSW and LPW per polymer in w%, on a dry matter basis.

Polymer	Waste Stream	Colour Composition
		Clear/Transparent	White	Black	Coloured
PET	Mixed MSW	6%	11.2%	-	82.8%
	LPW	42.9%	19.5%	37.4%	0.2%
HDPE	Mixed MSW	-	100%	-	-
	LPW	-	-	48.9%	51.1%
PVC	Mixed MSW	1.7%	1.3%	36.9%	60%
	LPW	17%	1.6%	0.6%	80.8%
LDPE	Mixed MSW	40.6%	3.6%	27.6%	28.2%
	LPW	8.4%	17.8%	7.7%	66.1%
PP	Mixed MSW	10.9%	22.8%	36.7%	29.6%
	LPW	7%	38.3%	21.6%	33.1%
PS	Mixed MSW	16.2%	10.5%	35.2%	38%
	LPW	29.4%	23.2%	17.4%	30%
Other	Mixed MSW	6.5%	55.9%	11.5%	26.1%
	LPW	11.3%	6.4%	43.2%	39.2%

and

Table A3. Colour composition of NPP in mixed MSW and LPW per area of application in w%, on a dry matter basis.

Area of Application	Waste Stream	Colour Composition
		Clear/Transparent	White	Black	Coloured
1. Building and Construction	Mixed MSW	4.3%	63.4%	4.3%	28%
	LPW	22%	-	24.9%	53.1%
2. Transport	Mixed MSW	-	-	100%	-
	LPW	-	-	99%	1%
3. Electronics	Mixed MSW	14.3%	15.9%	39.2%	30.6%
	LPW	15.1%	29.1%	28.2%	27.6%
4. Furniture	Mixed MSW	-	-	19%	81%
	LPW	-	100%	-	-
5. Agriculture and Gardening	Mixed MSW	1.5%	-	42.5%	56%
	LPW	-	-	-	100%
6. Medicine	Mixed MSW	6.9%	59.2%	10%	23.9%
	LPW	8.3%	40.3%	8.2%	43.2%
7. Household	Mixed MSW	12.4%	25.1%	31.5%	31%
	LPW	19.4%	19.9%	8.2%	52.5%
8. Other	Mixed MSW	14.4%	13.6%	37%	35%
	LPW	11.9%	10.2%	38.7%	39.2%

in the Appendix A). A total of 45 w% of NPW discarded in mixed MSW was found to be primarily clear/transparent (10 w%) or white (35 w%). This trait is advantageous for subsequent sorting and recycling, as clear/transparent plastics have the highest market value and can be variably coloured [25,30,82]. White plastics can also be dyed to a different colour, but they cannot be turned clear [31]. However, the colouring per polymer type reveals that target polymers in mixed MSW are predominantly (67 w%) coloured or black. NPW discarded through LPW in comparison has a lower share of clear/transparent (12 w%) and white coloured objects (21 w%) but unlike NPW in mixed MSW, 76 w% of target polymers are clear/transparent and white (73 t/yr). These findings partially match with Faraca and Astrup [31] who found 10 w% of clear/transparent hard plastic waste. However, the share of white plastics was much lower with 7 w%.

A significant proportion of NPW in both waste streams are coloured with 31 w% in mixed MSW and 38 w% in LPW. However, hard plastic waste analysed by Faraca and Astrup [31] consisted of roughly double the amount of coloured plastics (66 w%). Coloured plastics have a lower market value and can negatively influence sorting and recycling efficiency due to pigments changing the density of polymers and additionally leading to the discolouration of recycled plastics [30,82]. A detailed breakdown of colours found in NPW is listed in Figure S8 in the Supplementary File. Black coloured polymers not only hinder correct plastic sorting by interfering with NIR detection [29,30], but black plastics in various consumer products were also found to contain brominated flame retardants due to the reprocessing of plastic from historic waste electrical and electronic equipment in countries outside of the EU [32,83,84]. Around 37 w% of NPW made of PP in mixed MSW were coloured black, equalling more than 1100 t/yr. Considering the colouring per area of application, black coloured NPW were predominantly found in household products like coat-hangers or in the area Others amongst toys and non-assignable black plastic products. Between both waste streams, the mainly black coloured area Transport stands out. Similar colour distribution can otherwise be observed for the areas Electronics and Others. While Faraca and Astrup [31] have also found a high share of black plastic waste in the area “Automotive” (around 60 w%), their colour composition per area of application shows a much larger proportion of coloured plastics. These findings underpin the complexity of the NPW stream as well as the different characteristics of plastics from recycling centres in comparison to plastics from mixed MSW and separate collection.

The presence of impurities, including non-plastics such as metals or objects composed of multiple polymers, additionally influence the sorting and recycling efficiency of plastic waste as described in the introduction. Separately collected plastics undergo several reprocessing steps in sorting and recycling-facilities, including the separation of metals, where the rejection of metal-containing NPW can be assumed [26,31]. The total share of metal-containing NPW in both waste streams (Figure 5 and

Table A4. Share of NPP made of single-polymer, single polymer with metals, multi-polymer and multipolymer with metals per polymer type in mixed MSW and LPW, in w% (on a dry matter basis).

Polymer	Waste Stream	Presence of Impurities
		Single-Polymer	Single-Polymer + Metals	Multi-Polymer	Multi-Polymer + Metals
PET	Mixed MSW	81.2%	12.9%	6%	-
	LPW	48.6%	-	35.9%	15.6%
HDPE	Mixed MSW	100%	-	-	-
	LPW	48.9%	-	51.1%	-
PVC	Mixed MSW	9%	-	89.3%	1.7%
	LPW	79.2%	2.6%	11.9%	6.3%
LDPE	Mixed MSW	90.1%	-	8%	1.9%
	LPW	90.6%	-	9.4%	-
PP	Mixed MSW	41.7%	28.7%	28.6%	1.1%
	LPW	79.2%	4.7%	15.3%	0.8%
PS	Mixed MSW	70.2%	2.6%	18.3%	8.9%
	LPW	55.6%	19.3%	23.5%	1.6%
Other	Mixed MSW	65.7%	2.3%	31.1%	0.9%
	LPW	58.2%	9%	21.7%	11.1%

in the Appendix A) equals 13 w%, with PP in mixed MSW showing a metal-proportion of nearly 30 w%, originating from toys or shavers. Faraca and Astrup [31] found 10 w% of interfering materials, however, including paper, wood and other materials which were not analysed in the present study (see Section 3.5). The proportion of multi-polymer objects was found to be higher in mixed MSW (32 w%) than in LPW (19 w%), indicating a significant difference between the two waste streams and between hard plastic waste from recycling centres, where 11 w% consisted of multi-polymer products [31]. The largest proportion per polymer type was found amongst PVC discarded in mixed MSW, with 80 w%. However, the group of multi-polymer NPW consisted of 43 w% other polymers in mixed MSW and 54 w% in LPW. Associated product types encompass toys, sponges and body cleansing and personal care items such as toothbrushes.

Around 55 w% of NPW found in mixed MSW consisted of single-polymer objects, specifically 52 w% of target polymers (2150 t/yr). In contrast, the share of single-polymer objects in LPW amounted to 68 w%, with 74 w% (118 t/yr) of target polymers consisting of only one polymer type. One of the highest proportions of single-polymer objects was found in the area Others within the non-assignable product types, including fragments and non-identifiable plastic objects. Here, the share of single-polymer objects reached approximately 80 w% in mixed MSW and 83 w% in LPW. Notably, nearly 80 w% of all samples in this category were found in LPW (see Figure 2b in Section 3.2). This suggests that if consumers voluntarily discard NPW via separate collection, despite not being advertised as such, they are more likely to do so with clearly single-polymer items that are free of impurities. NPW discarded through LPW have therefore been shown to possess a higher quality regarding polymer composition, colouring and presence of multi-polymer objects and impurities. However, these NPW constitute merely 3 w% of the total NPW-amount in mixed MSW. When filtering for NPW in mixed MSW that are made of targeted polymers and are transparent, white and monochromatic as well as monopolymer-objects, a total amount of only 510 t/yr are recyclable on a high-quality level.

3.5. Research Gaps of NPW and Design for Recycling Recommendations

The present study offers new data concerning NPW, especially in mixed MSW in Vienna. However, the following factors must be taken into consideration for further studies, which can also be partly addressed with design for recycling recommendations:

Firstly, no seasonal variations were taken into consideration during the sampling campaign. While the samples taken were representative of the waste constitution of Vienna, the case study is geographically limited, and further research is required to interpret the results presented on a national level. Additionally, the analysis of other NPW-rich waste streams, like bulky waste [45], should be considered.

Furthermore, this study has assigned NPW to the category Kitchen-use products. However, during the analyses it was not determined whether items in this category actually consisted of food contact materials according to [77], which is recommended to accurately predict the share of potentially high-quality NPW. This should be envisaged in the future by analysing the presence of the “for food contact” symbol [77]. Regarding symbols, the low share of NPW with a RIC was noticeable. With the introduction of the packaging and packaging waste regulation [16], harmonised labelling of all packaging material will be introduced by 2028. This could also be extended to include NPW to ensure transparency regarding the polymer composition of NPW and to enable easier sorting and identification of NPW in recycling centres.

A detection of polymers present in the individual NPW items was conducted, including distinctions between mono- and multi-polymer items. It should, however, be noted that no manual separation was carried out during this step. This is equally applicable to metal components, where their presence was noted, but no manual disassembling steps were performed due to the complexity and non-dismantlability of most items, as well as due to the large number of individually analysed NPW items. In addition to metals, no additional interfering materials, such as paper stickers, were noted as well as potentially recycling-obstructive additives or carbon fibres. For future studies, it is recommended that these characteristics be included in the analysis to enable an even better understanding of the NPW stream. Regarding design for recycling, it is recommended to produce separable products to avoid cross-contamination from multi-polymer items, as is stated by Eriksen and Astrup [33], and also to prevent the loss of metal-containing plastics in sorting facilities [26,31].

As stated in Section 3.4, the colour of plastics not only influences subsequent recycling and the market value of recycled plastic material, but also the sorting efficiency. The limited use of dyes, as is also recommended in design for recycling guidelines for packaging [25,30,82], should also be applied to non-packaging plastics, especially for high-quality food contact products. Furthermore, the share of <5 cm NPW items is expected to be larger than presented in the results. The determination of the <5 cm items has only been conducted via measuring tape and not via sieve to ensure the characterisation of the majority of NPW samples. In a sorting facility, however, items like toothbrushes are very likely to be screened out, ending up in the output-stream for refuse-derived fuel [26], potentially lowering the actual share of recyclable NPW. In order to more reliably and accurately determine the fraction <5 cm and to better facilitate interpretation of the results presented, the usage of a sieve while carrying out hand-sorting is recommended for further studies. Non-packaging plastics should additionally be designed in a way that enables their sorting and subsequent recycling. In particular, for products like toys, where the results have shown a high share of <5 cm articles, or regularly disposed-of consumer goods regulations for better sortability could be considered.

Lastly, due to the longer use phases of non-packaging plastics in comparison to plastic packaging and their varying areas of application, NPW may contain additives that hinder the quality of recycled material. While Lipp et al. [85] demonstrated comparatively favourable recycling behaviour of NPW relative to plastic packaging, both recovered from mixed MSW, other studies found a contamination during the recycling process due to NPW [9,32,74]. While the present study did not investigate the presence or types of additives in the samples analysed, it is highly recommended that such contents be investigated in future research to obtain a comprehensive understanding of the NPW stream and to facilitate appropriate handling of these plastics, depending on their material composition.

4. Conclusions

To reinforce the circular economy and a more sustainable management of all plastic waste, a sound knowledge base of qualities and quantities of non-packaging plastic waste (NPW) is essential. Consequently, an in-depth characterisation of rigid non-packaging plastic both in mixed municipal waste (MSW) and separately collected lightweight packaging waste (LPW) was conducted in the city of Vienna for 2022. In particular, for NPW found in the first waste stream, little data is available.

This study found 4100 t/yr of NPW in mixed MSW containing target polymers that are currently lost for further recycling, predominantly polypropylene. However, the share of currently non-targeted polymers, including other polymers and PVC, reaches approximately 50 w% in both waste streams, with a total of 50 different polymer types found, conveying the heterogeneity of the NPW stream. Regarding recycling hindering characteristics, the study found 55 w% of coloured or black polymers and 45 w% of multi-polymer objects or objects where metal impurities were present. Only 6 w% of NPW in mixed MSW would be available for high-quality recycling. While NPW discarded through LPW shows better recycling relevant characteristics, this stream only amounts to 290 t/yr.

Distinguishing NPW according to areas of application additionally revealed that most objects in both waste streams originate from Household and Others (51 w% in mixed MSW and 73 w% in LPW), with Kitchen-use products (e.g., beverage bottles), which mainly consist of high-quality food contact material, being more often found in LPW. The inclusion of these products in an EPR scheme could therefore enable a closed-loop collection of high-quality polymers for recycling. To prevent contamination of currently collected LPW with other polymers, the collection of the remaining NPW in recycling centres could be considered. To increase recycling of NPW, especially of short-lived consumer goods, the establishment of design for recycling guidelines, including separability of products, limited usage of dyes and a regulation of small-scale products <5 cm should be examined.

The conclusions derived from this study are relevant for other regions and countries in the EU and beyond. A catalogue of recycling-influencing characteristics was provided as well as recommendations for design for recycling. Furthermore, the usage of an improved catalogue for the characterisation of non-packaging plastics in waste sampling campaigns gives important feedback to producers of non-packaging plastic products, facilitating the implementation of better design properties for the purpose of recycling. While further research is needed, especially regarding the presence of additives in NPW, the present study, together with other studies, extends the potential for a comprehensive characterisation on non-packaging plastics and hence facilitates future recycling and a more sustainable management of this large plastic waste stream.